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Meteorology Part II

CAAC ATPL Study Material

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The following study material is an extract from Li Weidong (2nd edition) 2012, The Aviation Theory Course for Airline Transport Pilot.

1. Aviation weather servicesYou know that as pilot in command of an aircraft, you are required to familiarize yourself with all available information before beginning a flight. For a flight under IFR or any flight not in the vicinity of an airport that information must include the latest or most current weather reports and forecasts.

2. Surface analysis and constant pressure chartsSurface Analysis Chart

Surface analysis chart often referred to as a surface weather map, is the basic weather chart. The chart is transmitted every. 3 hours. The valid time of the map corresponds to the plotted observations. A date and time group in universal coordinated times (UTC) informs the user of when the conditions portrayed on the map were actually occurring. The surface analysis chart displays other weather information such as surface wind direction and speed, temperature, dew point, and various the other weather data The surface analysis chart can show the pressure patterns by lines called isobars, The isobars on a surface weather map represent lines of equal pressure reduced to sea level. It also includes the position of fronts, and areas of high or low pressure. Weather Chart Station Model



In the surface analysis chart, each reporting station is depicted on the chart by a small circle. The weather information pertaining to the station is placed in a standard pattern around this circle, and is called a station model (Figure 8-22).

The meaning and symbol that the method is explained as follows of every project: 1) Total sky cover -- The total sky cover is noted by special symbols, the meaning and symbol of total sky cover as Figure 8-23.

2) Cloud type -- In the surface analysis chart, the cloud type is noted by special symbols, the cloud name, English abbreviation and symbols are shown as Figure 8-24.



The sky cover of the low cloud is shown by a digit noted on the right of the symbol of the cloud, only the lowest cloud noted it. The bass of the low cloud is shown by digits, its unit is 100 meters, the height is used the above ground level (AGL).

3) Temperature and dew point -- Temperature and dew point are noted by degrees Celsius, if they are the negatives, prefixed by "_".

4) Present weather -- On the surface analysis chart, the present weather is shown with special symbols, Figure 8-25 is some important present weather and its symbol.

5) Visibility -- Visibility is noted by kilometres.

6) Sea level pressure -- Sea level pressure is always shown in three digits to nearest tenth of an hPa. For 1 000 hPa or greater, prefix a "10" to the three digits. For less than 1 000 hPa, prefix a "9'' to the three digits. For example: if the sea level pressure shown in "132", the actual sea level pressure is 1 013.2 hPa.

7) Pressure change in past 3 hours -- the actual change is in tenths of an hPa. For example: if the pressure change in past 3 hours shown in "26", the actual pressure change in past 3 hours is increased steadily or unsteadily by "2.6" hPa.

8) Wind -- The wind direction expressed with arrow pole, the direction of the arrow points to the station circle, shows the direction that wind comes from. The wind speed is expressed with long or short arrow feather. See Figure 8-26.



9) Weather in the past -- The weather in the past showed the weather phenomenon appearing in 6 hours before being observed in the past, express with Figure 8-27 listed the forms of the symbols.

10) 6 hours precipitation -- Precipitation in 6 hours before the precipitation shows that is observed, it is expressed with millimetre. If it is expressed with "T", showing that the precipitation in 6 hours is smaller than 0.1 mm.

According to the explanation above, we can read the information of the weather station.

In Figure 8-28, the total sky cover is breaks in overcast, the high cloud type is cirrus, the middle cloud type is altocumulus, the low cloud type is stratocumulus, the cloud cover of stratocumulus is 5/10, the bass of the stratocumulus is 1 500 m (AGL). The temperature is 2 and the dew point is 1 . The present weather is smoke, visibility 4 kilometers. The sea level pressure is I 008.1 hPa, the pressure change in past 3 hours have reduced 2.1 hPa. Southeast wind at 2 m/s.



The data of the weather in the past and the 6 hours precipitation seldom appear, so we can not often see them.

Analysis

There are some another important contents in the surface analysis char, they are: isobars, pressure systems, fronts, same weather area, the center of pressure change in past 3 hours.

1) Isobars -- Isobars are solid lines depicting the sea-level pressure pattern and are usually spaced at 2.5 hectopascal (hPa). Each isobar is labeled. For example, 1 000 signifies 1 000 hPa, and 997.5 signifies 997.5 hPa.

2) Pressure systems --The letter "L" denotes a low pressure center, and the letter "H" denotes a high pressure center. The pressure of each center is indicated by a three- or four-digit number that is the center pressure in hPa. (Figure 8-29).

3) Fronts -- The analysis shows positions and types of fronts by symbols in figure 8-30. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. If the front has arrowhead-shaped symbols, it is a cold front. On the colored surface analysis chart, it is noted by a blue solid line.

If the front has half-moon shaped symbols, it is a warm front. On the colored surface analysis chart, it is noted by a red solid line. If the front has a arrowhead-shaped





symbols and a half-moon shaped symbols they are on the other side, it is a stationary, front (noted by a red and a blue solid line). If the two symbols are on the same side, it is a occluded front (noted by a purple solid line).

4) Same weather area -- On the surface analysis chart, the same weather areas are noted by a close line. At the center, there is a symbol showing that in this area every station has the same weather. The symbols of the same weather areas showing on Figure 8-31.

5) The center of pressure change in past 3 hours -- In the places that most greatly changes are occur we show them with a dashed line circle, and if the pressure change value is a positive number, it is noted by a blue "+", and followed by the pressure change value. If the pressure change value is a Negative number, it is noted by a red "-", and followed by the pressure change value. See the Figure 8-32.

Using The Chart

The surface analysis chart provides a ready means of locating pressure system and fronts. It also gives an overview of winds, temperatures, and dew point temperatures at chart time. When using the chart, keep in mind that weather moves and condition change. Using the surface analysis chart in conjunction with other information gives a more complete weather picture.





Figure 8-33 is a section of a surface analysis chart, it shows a low pressure center with a warm front. In the middle of the picture, there is a cold front, and a precipitation area. In this weather area there are rain shower and thundershower. At the upper left comer there is a high pressure center. In the north of Beijing there is a strong wind and sandstorm area. The area arrow A pointed is a center of pressure change in past 3 hours, for past three hours, the pressure have increased 2.5 hPa.

Constant Pressure Charts

Because the weather phenomenon takes place in the three-dimensional space, and analyses only according to one surface analysis chart is not enough obviously. In order to observe the weather condition of the three-dimensional space in detail, beside analysing the weather map of ground, we should analysis the constant pressure charts.

Space surface that point makes up that atmospheric pressure equal is called the constant pressure surface or isobaric surface. Because the same to go to atmospheric pressure of all parts its altitude can't the same, so isobaric surface is not a horizontal plane, but a surface as uneven as topography.

Constant pressure charts are similar in many ways to the surface analysis chart in that they show the pressure patterns and some weather conditions for reporting stations. These charts are prepared for selected values of pressure and present weather information at various altitudes. The standard charts prepared are the 850 hPa, 70 hPa, 500 hPa, 300 hPa, 250 hPa, and 200 hPa charts. Charts with higher pressure present information at lower altitudes, and Charts with lower pressure present information at higher altitudes. Figure 8-34 lists the general altitude (pressure altitude) of each constant pressure chart.



Plotted Data

Data from each observation station are plotted around a station circle on each constant pressure chart. The circle identifies the station position. The data plotted on each chart are temperature, temperature-dew point spread, wind, height of the surface above sea level. The temperature and temperature-dew point spread are in degrees Celsius, wind direction is relative to true north, wind speed is in m/s, and height is in meters. Figure 8-35 is a station model of the data plot.

Illustrate

Wind -- Wind direction and speed are plotted by symbols. The method to express the wind direction and speed are the same as it used in the surface analysis chart.

HGT -- Plotted height of the constant pressure surface in meters above mean sea level. If data is missing, nothing is plotted in this position.

T -- Plotted temperature to the nearest whole degree Celsius. A below-zero temperature is prefaced with a minus sign. Position is left blank if data is missing.

T-Td -- Plotted temperature-dew point spread to the nearest whole degree Celsius. Position is left blank if data is missing. According to the explanation above, we can read the information of the record station.

In Figure 8-36 (10s the temperature is , temperature-dew point spread is 5. , the height of the constant pressure surface is 3 040 m, northwest wind at 6 m/s. We can know that this is a data of the 700 hPa isobaric surface. In Figure 8-36 (b), the temperature is -1, temperature-dew point spread is 3.5 ~C, the height of the constant pressure surface is 5 800 m, southwest wind at 26 m/s. We can know that this is a data of the 500 hPa isobaric surface.



Analysis

All constant pressure charts contain analyses of height and temperature variations. Variations of height are analysed by contours, variations of temperature by isotherms.

Contours -- Contours are lines of constant height, in meters, which are referenced to mean sea level. Contours are used to map the height variations of surfaces that fluctuate in altitude. They identify and characterize pressure systems on constant pressure charts Contours are drawn as solid lines on constant pressure charts, the contour interval is the height difference between analyzed contours the standard contour interval is 40 meters. Contours are identified by a three-digit code located on each contour, to determine the contour height value, affix "zero" to the end of the code. For example, a contour with a "312" code on the 700 hPa chart identifies the contour value as 3 120 meters. Also, affix a "one" in front of the code on all 200 hPa contours and on 250 hPa contours when the code begins with zero. For example, a contour with a "044" code on a 250 hPa chart identifies the contour value as 10 440 meters.

The contour gradient is the distance between analyzed contours. Contour gradient identify slopes of surfaces that fluctuate in altitude. Strong gradients are closely spaced contours and identify steep slopes. Weak gradients are widely spaced contours and identify shallow slopes.

The contour analysis displays height patterns. Common types of patterns are lows, highs, troughs, and ridges. Contours have curvature for each of these patterns. Contours patterns can be further characterized by size and intensity. Size represents the breadth of a system. Sizes can range from large to small. A large pattern is



generally more than 1000 miles across, and a small pattern is less than 1 000 miles across. Intensities can range from strong to weak. Stronger systems are depicted by contours with stronger gradients and sharper curvatures. Weaker systems are depicted by contours with weaker gradients and weaker curvatures. For example, a chart may have a large, weak high, or a small, strong low.

Contour patterns on constant pressure charts can be interpreted the same as isobar patterns on the surface chart. For example, an area of low height is the same as an area of low pressure.

Winds respond to contour patterns and gradients. Wind directions parallel contours. In the Northern Hemisphere, when looking downwind, contours with relatively lower heights are to the left and contours with relatively higher heights are to the right. Thus, winds flow counterclockwise (cyclonically) around lows and clockwise (anticyclonically) around highs. (In the Southern Hemisphere these directions are reversed.) Winds that rotate are termed circulations. Wind speeds are faster with stronger gradients and slower with weaker gradients. In mountainous areas, winds are variable on pressure charts with altitudes at or below mountain crests. Contours have the effect of "channeling" the wind.

Isotherms -- Isotherms are lines of constant temperature. An isotherm separates colder air from warmer air. Isotherms are used to map temperature variations over a surface.

Isotherms are drawn as bold, dashed lines on constant pressure charts. Isotherm values are identified by a two-digit block on each line. The two digits are prefaced by "+" for above-freezing values as well as the zero isotherm and "-" for below-freezing values. Isotherms are drawn at 4-degree intervals on each chart. The zero isotherm separates the above-freezing and below- freezing temperatures.

Isotherms gradients identify the magnitude of temperature variations. Strong gradients are closely spaced isotherms and identify large temperature variations. Weak gradients are loosely spaced isotherms and identify small temperature variations.

Trough-line and shear line -- An elongated area of low pressure to be called trough, with the lowest pressure along a line marking maximum cyclonic curvature to be called trough-line. The shear-line is a field discontinuous line of wind with cyclone type shear, the wind direction, wind speed of both sides in shear-line have obvious differences. Trough-line and shear-line are the weather systems that are often seen on constant pressure charts, it is the important part in the synoptic analysis too.

Using the Chart

Figure 8-37 is a constant pressure chart of 700 hPa, In this upper air weather map, we



can see that near Lanzhou it is a high pressure center, there is a high-pressure system in the eastern area of China too. There is a low pressure system in the area of Mongolia; EF is a trough-line. MN is a shear-line appearing between two pieces of high pressure. Near Beijing it is a warm air center, there is a cold center in the east of Korea Peninsula. You can meet the turbulence while crossing the trough-line or the shear line while flying.

The upper air constant pressure chart can be used to locate the jet stream and its associated turbulence and wind shear. When there is a large change in wind speed over a short distance, the probability, of turbulence is greatly increased. Since the jet stream is associated with discontinuities in the temperature lapse rate at breaks in the tropopause, closely spaced isotherms indicate the possibility of turbulence or wind shear.



In 300 hPa, 250 hPa or 300 hPa constant pressure charts, the area where the wind speed is greater than 30 m/s is the position where the upper jet locations. The torrent in the high altitude is a contour compact district. Figure 8-38 is a constant pressure chart of 300 hPa, in this upper air weather map, we can see a upper jet is set out from the Caspian Sea, through the Balkash Lake, entry Xinjiang of China, then through Chengdu and Beijing, enter the Northeast area of Asia. The upper jet is a very strong place of a wind shear, and flies in the upper jet or crosses it, will meet the stronger clear air turbulence (CAT).

3. Significant weather prognostic chartsSignificant weather prognostic charts, called progs, it depicts weather conditions that are forecast to exist at a specific time in the future shown on the chart, portray forecast weather to assist in flight planning. Each valid time is the time at which the forecast conditions are expected to occur. Forecasts are made from a comprehensive set of



observed weather conditions. The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes. Forecasts are made for various periods of time. A 12-hour prog is a forecast of conditions which has a valid time 12 hours after the observed data base time, thus a 12-hour forecast. A 24-hour prog is a 24-hour forecast, and so on. For example, a 12-hour forecast based on O0Z observations is valid at 12Z. Altitude information on the prog charts is referenced to mean sea level (MSL) and compatible with aviation. Altitudes below 18 000 feet are true altitudes while above 18 000 feet are pressure altitudes or flight levels (FL).

The significant weather prognostic charts are generally divided in three kinds of height layer to offer:Low-Level Significant Weather Prog Chart (SWL) -- the flight height is lower than FL100 (10 000 feet).Middle-Level Significant Weather Prog Chart (SWM) -- the flight height is from FL 100 to FI.250 (10 000 feet - 25 000 feet). High-Level Significant Weather Prog Chart (SWH) -- the flight height is from 25 000 feet to 63 000 feet. This encompasses FL250 to FL630.

Main Content

There are the following several items in the main content of significant weather prognostic charts:

1) Significant weather -- (or calls the abominable weather), see form Figure 8-39 in kind and symbol of the significant weather, express with the symbol on the progs.

2) Important weather system -- For instance ground fronts line, high or low pressure center, convergence line and the intertropical convergence zone and so on (whether system symbols are shown in Figure 8-40).

3) Cloud accompanying with the significant weather --The clouds accompanying with the significant weather are described by simple language, the cloud type is noted by abbreviations.

On the significant weather prognostic charts, the significant weather and cloud district range are enclosed with the wavy line. Some important weather and cloud also stamp the height of bass and tope, also prove with the simple language sometimes.

Cloud type:

CI = Cirrus CC = Cirrocumulus CS = Cirrostratus CU= Cumulus AS = Altostratus SC = Stratocumulus NS = Nimbostratus ST = StratusAC = Altocumulus CB = Cumulonimbus





Cloud amount:

Clouds except CB FEW = few (1/8 to 2/8) SCT = scattered (3/8 to 4/8) BKN -- broken (5/8 to 7/8) OVC = overcast (8/8) SKC = sky clear (0/8)

CB only LOC = some places have CBs (local) ISOL = individual CBs (isolated) OCNL = well-separated CBs (occasional) FRQ = CBs with little or no separation (frequent) EMBD = CBs embedded in layers of other clouds or concealed by haze (embedded)

Cloud heights:

Heights are indicated on SWH and SWM charts in flight levels (FL), top over base. When XXX is used, tops or bases are outside the layer of the atmosphere to which the chart applies.

In SWL, charts:i) Heights are indicated as altitudes above mean sea level; ii) The abbreviation SFC is used to indicate ground level.

4) Depicting of lines and systems on specific chartsModels SWH and SWM -- Significant weather charts (high and medium)

Scalloped line = demarcation of areas of significant weather

Heavy broken line = delineation of area of CAT

Heavy solid line interrupted By wind arrow and flight level = position of jet stream axis with indication of wind direction, speed in KT or km/h and height in flight levels.

Figures on arrows = speed in KT or km/h of movements of frontal system

Flight levels inside small rectangles = height in flight levels of tropopause at spot locations, e.g. 340. Low and High points of the tropopause topography are indicated by the letters L or H respectively inside a pentagon with the height in flight levels.

Model SWL -- Significant weather charts (low level) X = position of pressure centers given in hectopascalsL = center of low pressure



H = center of high pressureScalloped lines = demarcation of area of significant weather Dashed lines = altitude of 0°C isotherm in feet or meters

NOTE: 0°C level may also be indicated by 0°: 060, i.e. 0°C level is at an altitude of 6,000 ft.Figures on arrows = speed in KT or km/h of movement of frontal systems, depressions or anticyclones Figure inside the state of the sea symbol = total wave height in feet or metres Figure inside the sea-surface temperature symbol = sea-surface temperature in °C.Figures inside the strong surface wind symbol = wind in KT or km/h.

5) Arrows and feathersArrows indicate direction. Number of pennants and/or feathers correspond to speed. Pennants correspond to 50 kt or 93 km/h Feathers correspond to 10 kt or 18 km/h Half-feathers correspond to 5 kt or 9 km/h1 knot = 1.852 kilometres per hour Low-level Significant Weather Prog Chart (SWL)

Low-level Significant Weather Prog Chart (SWL)

The low-level significant weather prog chart forecasts weather conditions from the surface to the FL100. In the pictures, it denotes the fronts and its movement that is expected (express direction with arrow point, show the speed of moving with number value, unit km/h or KT). And it indicates the various kinds of important weather, precipitation and the weather phenomenon which cause visibility lower than 5 000 m on a large scale (whether visibility use number value, unit meter), and the area and height to be influenced.

Figure 8-41 is a low-level significant weather prog chart, from this chart we can see that on the course from Shenyang to Harbin, the weather system passing is a cold front near Shenyang, a warm front near Harbin, There are the significant weather that may be met on the course: rainfall near Harbin, the area of Changchun is remarkable mountain waves, there is freezing precipitation, the thunderstorms, there is moderate and severe turbulence, near Shenyang. There is moderate aircraft icing.

Middle-level Significant Weather Prog Chart (SWM)

Compared with the low level Prog Charts, the middle level significant weather Prog charts have much different. There is no surface visibility,, no low pressure or high pressure centers, no altitude of isotherm, no sea-surface temperature and no stat of the sea, and have added the meteorological condition of flight appeared in Middle altitude. There is the weather:



1) Heavy broken line delineation of area of clear air turbulence (CAT), and its intensity is denoted by symbols.2) Heavy solid line show the position of jet stream axis with indication of wind direction, interrupted by wind speed in KT or km/h and height in flight levels. 3) Ash cloud (AV).

Figure 8-42 is a middle-level significant weather prog chart, on this chart we can see that on the course from Haikou to Guangzhou, the weather system passing is the intertropical convergence zone and a upper jet near Sanya, a quasi-stationary front near Guangzhou. There are the significant weather that may be met on the course: severe clear air turbulence near Haikou, the north of Haikou is remarkable mountain waves, the thunderstorms, there is severe turbulence, and moderate aircraft icing.



High-level Significant Weather Prog Chart (SWH)

The high-level significant weather prog chart forecasts conditions from 25 000 feet to 60 000 feet. This encompasses FL250 to FL600.

High-level significant weather prog chart have predicted all weather phenomenon of the middle level, unlike it the cloud only predicts cumulonimbus, still have the height in flight levels of tropopause, the unit is 100 feet.

Figure 8-43 is a high-level significant weather prog chart, on this chart we can see that on the course from Chongqing to Kweilin, the weather system passing is a worm front, a severe squall line and a upper jet. ]'here are the significant weather that may be met on the course: severe clear air turbulence and the thunderstorms.



4. Wind and temperatures aloft forecastWind and temperatures aloft forecast is supplied in chart form to flight crew members before departure, the charts shall be fixed time prognostic charts for standard isobaric surfaces. This prediction is very important while doing the flight plan.

Upper wind and upper-air temperatures forecast charts usually for points separated by no more than 500 km (300 nm) and for the following regular height layers.

FL 50 (850 hPa) FL 100 (700 hPa) FL 180 (500 hPa) FL 240 (400 hPa)FL 300 (300 hPa) FL 340 (250 hPa) FL 390 (200 hPa) FL 450 (150 hPa)

On upper wind and upper-air temperatures forecast charts, the wind speed is noted by knots, the method of marking of the wind speed as in Figure 8-44.

In the wind and temperatures aloft forecast charts, the temperatures is noted by degrees Celsius they are all negatives unless prefixed by "+".



Now, we can read the information about Figure 8-45, the wind direction is southwest, wind speed is 60 knots, temperatures is -4 .

Figure 8-46 is a party of a wind and temperatures aloft forecast chart, in this picture we know that in this area all lean towards the west wind, strong wind area lies in the Northeastern part pursued, low temperature area lie the Northeastern part pursued.

Where upper wind and upper air temperature information is supplied in tabular form, it should include data for the same flight levels as for upper-air charts. This information should be given for Examples of the form of presentation of tabular forecasts of upper winds and upper-air temperatures are given in Figure 8-47.

In figure 8-47, the boxes refer to spot winds degrees true and knots at intersections of latitude/longitude lines covered by the box. Temperatures in degrees Celsius, heights are above MSL (thousands of feet).

Example

“24 260 40 -28”, the ones that showed are: height 24 000 feet, wind 260 degrees at 40 knots, temperature -28 degrees C.





5. Aviation routine weather report (Metar)During preflight planning, the surface aviation weather report allows you to assess existing conditions and evaluate the accuracy of forecasts. You do this by comparing current reports with the forecast weather for the same time period to see if the weather is materializing as forecast. You can also review several previous reports to get a general idea of the weather trend. A current report also indicates weather your destination is presently above VFR or IFR minimums, as appropriate. If it is not and the forecast calls for only slight improvement by your estimated time arrive, the destination weather may not permit you to land. The surface report also is important at airports without a control tower or flight services station, since the last surface observation is the latest official weather available at that location.

The aviation routine weather report contains various weather elements in a coded form. The elements of the report are:

A. Type of report; F. Runway visual range (RVR) (as required); B. ICAO station identifier; G. Weather phenomena;C. Date and time of report; H. Sky condition;D. Wind; I. Temperature/dew point group; E. Visibility; J. Altimeter setting.

Format of the METAR Telegram



Key to the Metar Observations

Type of report (METAR or SPECI)There are two types of surface aviation weather reports-- the METAR and the aviation selected special weather report SPECI.

The METAR is taken on the hour, the SPECI is an unscheduled observation indicating a significant change in one or more elements of the weather. ICAO station identifier (CCCC)

The METAR code uses ICAO 4-letter station identifiers, some city's 4-letter station identifiers as Figure 8-48.

Time of report (YYGGggZ)

The time the observation is taken is transmitted as a six-digit time group appended with a Z to denote Coordinated Universal Time (UTC), indicate the date, hour and minute.

Wind (dddffGfmfm= MPS)

The wind is reported as a five-digit group, the first three digits is the direction the wind is blowing from in ten's of degrees, or "VRB" if the direction is variable. The next two digits is the speed in meters per second (MPS), if the wind is gusty, it is reported as a "G" after the speed followed by the highest gust reported. 00000 MPS for calm; for METAR, if direction vanes 60 degrees or more. Variability appended, e.g. 180V260.



Visibility (VVVVDv VxVxVxVxDv)

Visibility- is reported in meters. When the visibility is not the same in different directions the lowest visibility should be reported and its general direction in relation to the site of meteorological station indicated by reference to one of the eight points of the compass. VxVxVxVxDv Shows the greatest visibility, and direction. "9999" express visibility 10 kilometers.

Runway visual range (RVR) (RDrDr/VrVrVrVri)

The "R' identifies the group followed by the runway heading, a "/", and the visual range in meters. The letter "i" shows the change of the visual range in the runway in 10 minutes before observes. "U" show the visual range in the runway has the tendency to obviously rise when observing. "D" shows there are obvious downward trends in the visual range in the runway when observes, "N" shows there is no obvious change in the visual range in the runway when observes.

Weather phenomena

In METAR, weather is reported in the format: Intensity, Proximity, Descriptor, Precipitation, Obstruction to visibility, or Other.

Intensity -- applies only to the first time of precipitation reported. A "-" denotes light, no symbol denotes moderate, and a "+" denotes heavy.

Proximity -- applies to and reported only for weather occurring in the vicinity of the airport (between 5 and 10 miles of the center of the airport runway complex). It is denoted by the letters "VC".

Descriptor -- these seven descriptors apply to the following precipitation or obstructions to visibility:

TS -- thunderstorm BL -- blowingSH -- shower DR -- low driftingFZ -- freezing MI -- shallowBC -- patches

Precipitation -- there are eight types of precipitation in the METAR code:

RA -- rain GR -- hailDZ -- drizzle GS -- small hail/snow pellets SN -- snow PE -- ice pelletsSG -- snow grains IC -- ice crystals



Obstruction to visibility -- there are eight types of obstructing phenomena in the METAR code:

BR -- mist HZ -- hazeSA -- sand VA -- volcanic ash FU -- smoke FG -- fog DU -- dust PY -- spray Note: fog (FG) is reported only when the visibility is less than one kilometer otherwise mist (BR) is reported.

Other -- there are five categories of other weather phenomena which are reported when they occur.

SQ -- squall SS -- sandstormDS -- duststorm PO -- dust/sand whirls FC -- funnel cloud/tornado/waterspout

Examples

+SHRA -- heavy shower of rain TSSN -- moderate thunderstorm with snow FZDZ -- moderate freezing drizzle SNRA -- moderate snow and rain +TSSNGR -- heavy thunderstorm with snow and hail

Sky condition

The sky condition as reported in METAR represents a significant change from the way sky condition is currently reported. In METAR, sky condition is reported in the format: Amount, Height, (Type), or Vertical Visibility.

Amount -- the amount of sky cover is reported in eighths of sky cover, suing the contractions:SKC-clear (no cloud)FEW-few (1/8 to 2/8's of clouds) SCT-scattered (3/8's to 4/8's of clouds) BKN-broken (5/8's to 7/8's of clouds) OVC-overcast (8/8's of clouds)

Height -- cloud basses are reported with three digits in 30 of meters, the height is used the above ground level (AGL).

(Type) -- if towering cumulus clouds (TCU) or cumulonimbus clouds (CB) are present, they are reported after the height which represents their base.



Vertical Visibility- total obscurations are reported in the format "VVhhh" where VV denotes vertical visibility, and "hhh" is the vertical visibility in 30 of meters.

CAVOK- when it is better, word yards of CAVOK can be used for replacing the visibility group, weather phenomenon group and cloud group, its condition is:

• Potential visibility is 10 kilometers or the above;• 1500 meters under cloudless, and the sky does not have cumulonimbus, cumulus,

etc;• There is no significant weather phenomenon, such as precipitation, thunderstorm,

sandstorm, blowing snow, etc.

Temperature/dew point

Temperature and dew point are reported in a two-digit form in degrees Celsius. Temperatures below zero are prefixed with an “M”.

Altimeter setting

Altimeter settings are reported in a four-digit format in whole hectopascal (hPa), denote with a "Q", e.g. Q1003.

Examples and Explanations

Example 1

METAR ZGGG 061800Z 20007G11MPS 2000 TSRA SCT030 BKN050 (CB) 28/25 Q992 =

Explanation

Aviation Routine Weather Report, Guangzhou, date 06, time 1800UTC, wind 200 at 7, gusts 11MPS, visibility 2 000 meters, moderate thunderstorm with rain, 900 scattered, 1 500 broken, cumulonimbus, temperature 28°C, dew point 2 , altimeter 992 hPa.

Example 2

METAR YUDO 221630Z 24015KMH 0600 RI2/1000U FG DZ SCT010 OVC020 17/16 QI018 BECMG TLI700 0800 FG BECMG ATI800 9999 NSW =

Explanation

Routine report for Donlon/International issued on the 22nd of the month at 1630 UTC; surface wind direction 240 degrees; wind speed 15 kilometres per hour; visibility 600 metres; runway visual range representative of the touchdown zone for runway 12 is 1 000 metres and the runway visual range values have shown an upward tendency



during previous 10 minutes (RVR tendency to be included in METAR only); fog and moderate drizzle; scattered cloud at 300 metres; overcast at 600 metres; air temperature 17 degrees Celsius; dew-point temperature 16 degrees Celsius; QNH 1018 hectopascals; trend during next two hours visibility becoming 800 metres in fog by 1700 UTC; at 1800 UTC visibility becoming 10 kilometres or more and nil significant weather.

Example 3

SPECI RKSS 221315Z VRB03MPS 0600 +SN FG VV002 M01/M03 QI001 =

Explanation

Aviation selected special weather report, Seoul, date 22, time 1315UTC, wind variable at 3 MPS, visibility 600 meters, heavy, snow and fog, vertical visibility 60 meters, temperature -1 , dew point -3 , altimeter 1 001 hPa. The equal sign signifies the end of the METAR.

Example 4

SPECI YUDO 151115Z 05025G37KT 1200NE 6000S +TSRA BKN050CB 25/22 Q1008 TEMPO TLI200 0600 BECMG AT1200 8000 NSW NSC =

Explanation

Selected special report for Donlon / International issued on the 15th of the month at 1115 UTC; surface wind direction 50 degrees; wind speed 25 knots gusting between 10 and 37 knots (minimum wind speed not to be included in SPEC1); visibility lowest to north east at 1 200 metres, visibility 6 000 metres to south (directional variations to be included in SPECI only; visibility representative of the runway included in the local special report); heavy thunderstorm with rain; broken cumulonimbus cloud at 1 500 metres; air temperature 25 degrees Celsius; dew-point temperature 22 degrees Celsius; QNH 1 008 hectopascals; trend during next two hours, visibility temporarily 600 metres from 1 115 to 1 200, becoming at 1200 UTC visibility 8 km, thunderstorm ceases and nil significant weather and nil significant cloud.

6. The terminal aerodrome forecast (TAF)The terminal aerodrome forecasts are prepared to give a description of expected conditions at an airport and within a 5 nautical miles radius of a runway complex. A terminal aerodrome forecast is a concise statement of the expected meteorological conditions over a specified time period, usually 9 hours and 24 hours. The descriptors and abbreviations used in the TAF are the same as those used in the METAR report.



Format of the TAF Telegram

Key to the TAF

Type -- Routine (TAF), Amended (TAF AMD)Location -- ICAO four-letter location identifierIssuance date/time --A six-digit group giving the date (first two digits) and the time (last four digits ) in UTC.Valid period -- The valid period of the forecast is a two-digit date followed by the two-digit beginning and two-digit ending hours in UTC. Routine TAFs are valid for 9 hours or 24 hours. The 24 hours forecast are issued four times daily at 0000Z 0600Z 1200Z 1800Z All ending times throughout the TA F of 00Z are indicated by the number of 24.

Examples

111818 Forecast valid from the eleventh at 18Z to the twelfth at 18Z. 300024 Forecast valid from the thirtieth at 00Z to the first at 00Z.



Forecast--Body of the TAF has a basic format: WIND/VISIBILITY/WEATHER/SKY CONDITION

Wind- Five digits followed by "MPS", the first three are direction and last two speed.

Wind gust denoted by the letter "G" appended to the wind speed followed highest gust. Variable wind direction noted by "VRB" where direction usually appears, a calm wind (2 m/s less) is shown as 00000 MPS.

Visibility -- Visibility is reported in meters. The forecast methods are the same as those used in the, METAR report.

Weather--Weather phenomena significant to aviation are included and follow a format which is: Intensity or Proximity/Descriptor/Precipitation/Obstruction/visibility/Other."VC" applies to weather conditions expected to occur in the vicinity of the airport (between a 5 to 10 statute mile radius of the airport), but not at the airport itself Therefore, "VCTS" in a Terminal Aerodrome Forecast indicates thunderstorms are expected between a 5 to 10 statute mile radius of the airport, but not at the airport itself. If no significant weather is expected to occur during a specific time period in the forecast, the weather group is omitted or expressed with "NSW". However, if after a time period in which significant weather has been forecasted, a change to a forecast of "no significant weather" occurs, the contraction NSW (no significant weather) will appear as the weather included in BECMG (becoming) or TEMPO (Temporary) groups. NSW will not be used in the initial time period of a TAF or in FM

The FM group is used when a rapid and significant change, usually occurring in less than 1 hour, in prevailing conditions is expected. Appended to the FM indicator is the four-digit hour and minute the change is expected to begin. The forecast is valid until the next change group or the end of the current forecast.

Examples

FM 1500 16008G 14MPS 4000 SCT040 BKN250

FM0200 32005MPS 1000 TSRA FEW010 BKN050CB

Sky condition--Sky condition is presented in a format which includes Amount/Height (Type) or Vertical Visibility. The forecast methods are the same as those used in the METAR report. If there is no significant cloud, expressed with "NSC".

CAVOK-- when it is better, word yards of CAVOK can be used to forecast the visibility group, weather phenomenon group and sky condition group, its standard is the same as in the METAR.

Temperature predicted -- "T" is the yard denote for the temperature, "TrTr" is the



predicted temperature in degrees Celsius. Temperatures below zero are prefixed with an “M'. Ex: "TM03/04Z". means "It is estimated that the temperature is -3 at 0400UTC".

Icing -- "6" is the yard denote for icing, "hihihi" is the height of the icing layer bottom (= yard number~30 m ), "h" is the thickness of the icing layer (= yard number x 300 m ), "Ic" is the type of the icings, the method to work out telegram see Figure 8-47. Ex: "631002", means "there exist light icing in precipitation, the height of the icing layer bottom is 3 000 m, the thickness of the icing layer is 600 m."

Turbulence -- "5" is the yard denote for the turbulence, "hBhBhB" is the height of the turbulence laver bass (= yard number~30 m), "tL" is the thickness of the turbulence layer (= yard number 300m ), "B" is the type of the turbulence, the method to work out telegram is shown in Figure 8-49. Ex: "561204", means "there exist severe turbulences not frequent in clear air, the height of the turbulences layer bottom is 3 600 m, the thickness of the turbulences layer is 1 200 m."

Figure 8-49 The type of icings and turbulences

Other--Probability - A PROB40 HHhh group in a TAF indicates the probability of occurrence of thunderstorms or precipitation. PROB40 indicates a 40%- 49% chance and PROB30 indicates a 30%- 39% chance. The HHhh is a four-digit beginning and ending time.

TYPE YARD THE TYPE OF ICING THE TYPE OF TURBULENCE

0 No Icing No Turbulence

1 Light Icing Light Turbulence

2 Light Icing in cloud Moderate Turbulence not frequent in clear air

3 Light Icing in Precipitation Moderate Turbulence frequent in clear air

4 Moderate Icing Moderate Turbulence not frequent in cloud

5 Moderate Icing in Cloud Moderate Turbulence frequent in cloud

6 Moderate Icing in Precipitation Severe Turbulence not frequent in clear air

7 Severe Icing Severe Turbulence frequent in clear air

8 Severe Icing in cloud Severe Turbulence not frequent in cloud

9 Severe Icing in Precipitation Severe Turbulence frequent in cloud



Temporary conditions--Changes usually lasting less than an hour. TEMPO HHhh (beginning and ending time).

Forecast change groups -- Used when a significant or permanent change is expected. The change is indicated by the group FMHH (from) and BECMG (becoming) followed by HHhh (times).

The Telegram Examples

Example 1

TAF ZUUU 1111407 111212 13005MPS 5000 BKNI00 TEMPO 1214 3500 BR FM 1500 16008G15MPS 6000 SCT040 BKN250 TI6/20Z FM 0000 14006MPS 3500 BKN080 OVC150 PROB40 0004 2000 TSRA BKN030CB FM 0400 14008MPS 3000 SCT040 OVC080 TEMPO 0408 1500 TSRA OVC030CB BECMG 0810 32007MPS =.

Explanation

Aviation terminal forecasts Chengdu prepared on the 11th at 1140Z, valid period from the 11th at 1200Z until the 12th at 1200Z, wind 130 at 5 m/s, visibility 5 000 m, ceiling 3 000 m broken, temporary conditions between 1200Z and 1400Z, visibility 3 500 m, mist.

From 1500Z, wind 160 at 8 m/s gusting to 15 m/s, visibility 6 000 m, 1 200 m scattered, ceiling 7500m broken, temperature is 1 at 2000UTC.

From 0000Z, wind 140 at 6 m/s, visibility. 3 500 m, ceiling 2 400 m broken, 4 500 m overcast, 40% probability between 0000Z and 0400Z, visibility 2 000 m, thunderstorms with moderate rain showers, ceiling 900 m broken with cumulonimbus.

From 0400Z, wind 140 at 8 m/s, visibility 3 000 m, 1200 m scattered, ceiling 2 400 m overcast. Temporary conditions between 0400Z and 0800Z, visibility. I 500 m, thunderstorms with moderate rain showers, ceiling 900 m overcast with cumulonimbus, becoming between 0800Z and 1000Z, wind 320 at 7 m/s. The equal sign signifies the end of the TAF.

Example 2

TAF YUDO 160000Z 160624 13018KMH 9000 BKN020 BECMG 0608 SCT015CB BKN020 TEMPO 0812 17025G40KMH 1000 TSRA SCT010CB BKN020 FM1230 15015KMH 9999 BKN020 BKN 100 T26/18Z 621203 540502 =



Meaning of the forecast

Aerodrome forecast for Donlon/International issued on the 16th of the month at 0000 UTC valid from 0600 UTC to 2400 UTC on the 16th of the month; surface wind direction 130 degrees; wind speed 18 kilometres per hour; visibility, 9 kilometres, broken cloud at 600 metres; becoming between 0600 UTC and 0800 UTC, scattered cumulonimbus cloud at 450 metres and broken cloud at 600 metres; temporarily between 0800 UTC and 1200 UTC surface wind direction 170 degrees; wind speed 25 kilometres per hour gusting to 40 kilometres per hour; visibility 1000 metres in a moderate thunderstorm with rain, scattered cumulonimbus cloud at 300 metres and broken cloud at 600 metres; from 1230 UTC surface wind direction 150 degrees; wind speed 15 kilometres per hour; visibility 10km or more; broken cloud at 600 metres and broken cloud at 3 000 metres. Temperature is 26 at 1800UTC, there exist light icing in cloud, the height of the icing layer bottom is 3 600 m, the thickness of the icing layer is 900 m. There exist Moderate turbulences not frequent in cloud, the height of the turbulences layer bottom is 1500m, the thickness of the turbulences layer is 600 m.

Note -- In this example, the primary units "kilometres per hour" and "metre" were used for wind speed and height of cloud base respectively. However, units "knot" and "foot" may be used instead.

7. In-flight aviation weather advisoriesIn-flight aviation weather advisories are forecasts to advise en route aircraft of development of potentially hazardous weather. There are three types of in-flight aviation weather advisories -- the Significant Meteorological Information (SIGMET), the Airmen's Meteorological Information (AIRMET), and Convective SIGMET. In the In-flight Aviation Weather Advisories the more important are the SIGMET and AIRMET. They are issued to alert pilots to potentially hazardous weather not adequately forecast in the current Area Forecast (FA).

Significant Meteorological Information (SIGMET)

A SIGMET is issued to advise pilots of weather considered potentially hazardous to all categories of aircraft, and is valid for the period stated in the advisory. SIGMET information shall be issued by a meteorological watch office and shall give a concise description in abbreviated plain language concerning the occurrence and/or expected occurrence of specified en-route weather phenomena, which may affect the safety of aircraft operations, and of the development of those phenomena in time and space.

The Content of SIGMET

1) at subsonic cruising levels:



thunderstorm -- obscured OBSC TS-- embedded EMBD TS-- frequent FRQ TS-- squall line SQL TS -- obscured with hail OBSC TS GR-- embedded with hail EMBD TS GR -- frequent, with hail FRQ TS GR-- squall line with hail SQL TS GR

tropical cyclone -- tropical cyclone TC (+ cyclone name) with 10-minute mean surface wind speed of 63 km/h (34 KT) or more

turbulence -- severe turbulence SEV TURB

icing -- severe icing SEV ICE -- severe icing due to freezing rain SEV ICE (FZRA)

mountain wave-- severe mountain wave SEV MTW

duststorm -- heavy duststorm HVY DS

sandstorm --heavy sandstorm HVY SS

volcanic ash -- volcanic ash VA (+ volcano name, if known)

2) at transonic levels and supersonic cruising levels: turbulence -- moderate turbulence MOD TURB -- severe turbulence SEV TURB

cumulonimbus -- isolated cumulonimbus ISOL CB -- occasional cumulonimbus OCNL CB -- frequent cumulonimbus FRQ CB

hail -- hail GR



volcanic ash -- volcanic ash VA (+ volcano name, if known)

SIGMET information shall not contain unnecessary descriptive material. In describing the weather phenomena for which the

SIGMET is issued, no descriptive material additional to that given in a) and b) shall be included. SIGMET information concerning thunderstorms or a tropical cyclone shall not include references to associated turbulence and icing.

SIGMET information shall be cancelled when the phenomena are no longer occurring or are no longer expected to occur in the area.

Format and Exchange of SIGMET Messages

SIGMET messages shall be prepared in abbreviated plain language, using approved ICAO abbreviations and numerical values of self-explanatory nature.

The format of these advisories consists of a heading and text. The heading identifies the issuing Weather Service Forecast Office (WSFO), type of advisory, and the valid period. The text of the advisory contains a message identifier, a flight precautions statement, and further details if necessary.

The period of validity of a SIGMET message should be not more than 6 hours, and preferably not more than 4 hours.

Heading

A. ICAO location indicator of the ATS unit serving the FIR or CTA to which the SIGMET refers. Examples: YUDO ZBAA ZSSS.

B. Message identification and sequence number. Messages containing SIGMET information for subsonic aircraft shall be identified as "SIGMET", those containing SIGMET information for supersonic aircraft during transonic or supersonic flight shall be identified as "SIGMET SST". Separate series of sequence numbers shall be used for "SIGMET" and "SIGMET SST" messages. Examples: SIGMET 5, SIGMET SST 1.

C. Date-time groups indicating the period of validity in UTC. Examples: VALID 221215/221600.

D. Location indicator of MWO originating the message with a separating hyphen. Examples: YUDO--, ZGGG-Heading examples: YUDD SIGMET 2 VALID 101200/101600 YUSO ZUUU SIGMET 3 VALID 101345/101600 ZUGH



Text

A. Name of the FIR/CTA for which the SIGMET is issued or aircraft radiotelephony call sign.Examples: AMSWELL FIR, SHANLON FIR/UIR AMSWELL FIR/2

B. Detailed content. Description of phenomenon causing the issuance of SIGMET. (see a),b))

C. Indication whether the information is observed (OBS) and expected to continue, or forecast (FCST). Examples: OBS AT 2245Z.

D. Location (referring to latitude and longitude (in degrees and minutes) or locations or geographic features well known internationally)Examples: S OF N54, N OF N50, N2020 W07005

E. Flight level and extent. Examples: FL180, CB TOP FL390.

F. Movement or expected movement with reference to one of the eight points of compass, or stationary. Examples: MOVE 40KMH, STNR.

G. Expected changes in intensity, INTSF or WKN or NC. INTSF -- IntensifyWKN -- WeakenNC -- No change

H. Forecast position of volcanic ash cloud or the center of the TC at the end of the validity period of the SIGMET message. Examples:-- FCST 2200Z TC CENTRE N2740 W07345-- FCST 1700Z VA CLD 515 E075 TO S15 E081 TO S17 E083

I. Outlook providing information beyond the period of validity of the trajectory of the volcanic ash cloud and positions f the tropical cyclone center. Examples:--OTLK 260400 TC CENTRE N28030 W07430 261000 TC CENTRE N3100 W07600--OTLK 212300 VA CLD APRX S16 E078 TO 517 E084 TO S18 E089 TO S19 E081 TO S16 E078 220300 VA CLD PRX 517 E81 TO 518 E86 TO S20 E92 TO 521 E84 TO S17 E81.



Example of SIGMET Message

YUCC 5IGMET 5 VALID 221215/221600 YUDO --AMSWELL FIR SEV TURB OBS AT 1210Z YUSB FL250 MOVE 40KMH WKN Meaning:

The fifth SIGMET message issued for the AMSWELL flight information region (identified in abbreviated plain language and by YUCC Amswell area control center) by the Donlord International' meteorological watch office (YUDO) since 0001 UTC; the message is valid from 1215 UTC to 1600 UTC on the 22nd of the month; severe turbulence was observed at 1210 UTC over Siby/Bistock aerodrome (YUSB) at flight level 250; the turbulence is expected to move eastwards at 40 kilometres per hour and to weaken in intensity.

Airmen's Meteorological Information (AIRMET)

AIRMET Information

AIRMET information shall be issued by a meteorological watch office in accordance with regional air navigation agreement, taking into account the density of air traffic operating below flight level 100. AIRMET information shall give a concise description in abbreviated plain language concerning the occurrence and/or expected occurrence of specified en-route weather phenomena, which have not been included in the area forecast and may affect the safety of low-level flights, and of the development of those phenomena in time and space.

The format of the AIRMET is the same as the SIGMET. At cruising levels below flight level 100 (or below flight level 150 in mountainous areas, or higher, where necessary.):

surface wind speed -- widespread mean surface wind speed above 60 km/h (30 kt). SFC WSPD (+ wind speed and units)

surface visibility -- widespread areas affected by reduction of visibility to less than 5,000m, including the weather phenomenon causing the reduction of visibility. SFC VIS (+ visibility) (+ weather phenomenon)

thunderstorms -- isolated thunderstorms without hail ISOL TS-- occasional thunderstorms without hail OCNL TS-- isolated thunderstorms with hail ISOL TSGR-- occasional thunderstorms with hail OCNL TSGR



mountain obscuration -- mountains obscured MT OBSC

cloud information -- widespread areas of broken or overcast cloud with height of base less than 300 m (1 000ft) above ground level: -- broken BKN CLD (+ height of the base and top and units)-- overcast OVC CLD (+ height of the base and top and units) cumulonimbus clouds which are: -- isolated ISOL CB-- occasional OCNL CB-- frequent FRQ CB

towering cumulus clouds which are: -- isolated ISOL TCU-- occasional OCNL TCU -- frequent FRQ TCU

icing -- moderate icing (except for icing in convective clouds) MOD ICE

turbulence -- moderate turbulence (except for turbulence in convective clouds) MOD TURB

mountain wave -- moderate mountain wave MOD MTW

Example of AIRMET Message

YUCC AIRMET 2 VALID 221215/221600 YUDO-AMSWELL FIR MOD MTW OBS AT 1205Z AND FCST N48 El0 FL080 STNR NC Meaning: The second AIRMET message issued for the AMSWELL flight information region (identified in abbreviated plain language and by YUCC Amswell area control centre) by the Donlon/International meteorological watch office (YUDO) since 0001 UTC; the message is valid from 1215 UTC to 1600 UTC on the 22nd of the month; moderate mountain wave was observed at 1205 UTC at 48 degrees north and 10 degrees east at flight level 080; the mountain wave is expected to remain stationary and not to undergo any changes in intensity.



8. Pilot weather reportA pilot weather report (PIREP) is often the most timely source of information about such weather conditions as icing and multiple cloud layers. While area forecasts and freezing level charts can give the pilot a good idea of the potential for icing, only a PIREP can let the pilot know what is happening currently.

The Kind of the Plane Report

According to the stipulations of International Civil Aviation's Organization, The following aircraft observations shall be made:

A. routine aircraft observations and reports during en-route. B. special aircraft observations and report. C. the aircraft observations and reports during climb-out phases of the flight. Aircraft observations shall be reported during flight at the time the observation is made or as soon thereafter as is practicable.

Routine Aircraft Observations and Reports

Routine aircraft observations and report are made at the meteorological service report point in the regular flight. It produces automatically from the report system of the plane in flight or report by the pilots.

The place that must carry, on routine observing and report is: A. at which the applicable air traffic services procedures require routine position reports; andB. which are those separated by distances corresponding most closely to intervals of one hour of flying time.

When voice communications are used, in the following situations, an aircraft shall be exempted from making the routine observations:C. the aircraft is not equipped with RNAV equipment; or D. the flight duration is 2 hours or less; or E. the aircraft is at a distance equivalent to less than one hour of flying time from the next intended point of landing; or F. the altitude of the flight path is below 1 500 m (5 000 ft).

Special Aircraft Observations and Reports

The special aircraft observations and report refers to the report to the special weather phenomenon. Special observations shall be made by all aircraft whenever the following conditions are encountered or observed:



A. Severe turbulence; or severe icing; or severe mountain wave;B. Thunderstorms, without hail, that are obscured, embedded, widespread or in squall lines; or thunderstorms, with hail, that are obscured, embedded, widespread or in squall lines;C. Heavy duststorm or heavy sandstorm;D. Volcanic ash cloud; or pre-eruption volcanic activity or a volcanic eruption.

In addition, in the case of transonic and supersonic flights, the special observations shall be made: moderate turbulence; or hail; or cumulonimbus clouds.

The Aircraft Observations and Reports During Climb-out Phases of the Flight

When other meteorological conditions not listed under (2), e.g. wind shear, are encountered and which, in the opinion of the pilot-in-command, may affect the safety or markedly affect the efficiency of other aircraft operations, the pilot-in-command shall advise the appropriate air traffic services unit as soon as practicable.

When reporting aircraft observations of wind shear encountered during the climb-out and approach phases of flight, the aircraft type should be included. Where wind shear conditions in the climb-out or approach phases of flight were reported or forecast but not encountered, the pilot-in-command should advise the appropriate air traffic services unit as soon as practicable unless the pilot-in-command is aware that the appropriate air traffic services unit has already been so advised by a preceding aircraft.

Content of Air-reports

When voice communications are used, the elements contained in routine and special air-reports shall be:

Routine Air-reports

Message type designator

Section 1. Position information Aircraft identification; Position or latitude and longitude; Time

(l) (2) (3)Flight level or altitude; Next position and time over; Ensuing significant point

(4) (5) (6)

Section 2.Operational information Estimated time of arrival; Endurance

(7) (8)



Section 3. Meteorological information Air temperature; Wind direction; Wind speed; Turbulence Aircraft icing; Humidity (if available)

Special Air-reports

Message type designator

Section 1. Position information Aircraft identification; Position or latitude and longitude; Time: Flight Level or Altitude

(1) (2) (3) (4)

Section 3. Meteorological information Condition prompting the issuance of a special air-report, to be selected from the list presented under (2).

A PIREP is transmitted in a prescribed format (see Figure 8-50). Required elements for all PIREPs are type of repot,, location, time, flight level, aircraft type, and at least one weather element encountered. When not required, elements without reported data are omitted. All altitude references are mean sea level (MSL) unless otherwise noted. Distance for visibility is in statute miles and all other distances are in nautical moles. Time is in universal coordinated time (UTC).

Encoding PIREPs

UUA/UA - Type of repot: URGENT (UUA) - Any PIREP that contains any of the following weather phenomena: Tornadoes, funnel clouds, or waterspouts; Severe or extreme turbulence, including clear air turbulence (CAT);



Severe icing;Hail;Volcanic ash;Low-level wind shear (LLWS): (Pilot reports air speed fluctuations of 10 notes or more within 2 000 feet of the surface);Any other weather phenomena reported which are considered by the controller to be hazardous, or potentially hazardous to flight operations.

ROUTING (UA) - Any PIREP that contains weather phenomena not listed above, including low-level wind shear reports with air speed fluctuations of less than 10 knots.

/OV -- Location: Use VHF NAVAID (s) or an airport using the three- or four-letter location identifier. Position can be over a site, at some location relative to a site, or along a route. Ex:/OV ZGGG; /OV ZBAA 090025; /OV ZUGH 18010- SUUU; /OVZGGG-SGHK

/TM -- Time: Four digits in UTC. Ex:/TMI015

/FL -- Altitude/flight level: Tree digits for hundreds of feet with no space between FL and altitude, If not known, use UNKN. UNKN. Ex: FL095; FL310; FL

/TP -- Aircraft type: Four digits maximum; if not known, use UNKN. Ex: /TP L329; /TP B737; /TP UNKN

/SK -- Sky cover: Describes cloud amount, height of cloud bases, and height of cloud topes. If unknown, use UNKN. Ex: /SK SCT040 - TOP080; /SK BKN I. JNKN - TPO075; /SK BKN-OVC050-TOP UNKN; /SK SKC;

/WX -- Flight visibility and weather: Flight visibility (FV) reported first in standard METAR weather symbols. Intensity ( - for light, no qualifier for moderate, and + for heavy ) shall be coded for all precipitation types except ice crystal and hail. Ex:/WX FV05SM-RA; /WX FV 1,200M SN BR; /WX RA

/TA -- Temperature (Celsius): If below zero, prefix with an "M." Temperature shall also be reported if icing is reported. Ex: /TA 15; /TA M06. /WV --Wind:Direction from which the wind is blowing coded in tens of degrees using three digits.



Directions of less than 100 degrees shall be preceded by a zero. The wind speed shall be entered as a two- or three-digit group immediately following the direction, coded in whole knots using the hundreds, tens, and units digits. Ex: /WV25042KT; /WV 320110KT.

/TB -- Turbulence: Use standard contractions for intensity and type (CAT or CHOP when appropriate). Include altitude only if different from FL (see Figure 8-50). Ex: /TB EXTRM; /TB OCNL LGT-MOD BLW090; /TB MOD-SEV CHOP 080-110.

/IC -- Icing: Describe using standard intensity and type contractions. Include altitude only if different from FL(see Figure 8-51 ). Ex: /IC LGT-MOD RIME; /IC SEV CLR 028-045.

/RM -- Remarks:Use free form to clarify the report purring hazardous element first. Ex: /RM LI.WS-15KT SFC-030 DURC RWY22 TFK.


Intensity Aircraft Reaction Reaction Inside Aircraft

Light

Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch,

roll, yaw). Report as light turbulence or light CAT. or Turbulence that causes slight, rapid and

somewhat rhythmic bumpiness without appreciable changes in altitude or attitude.

Report as light CHOP.

Occupants may feel a slight strain against belts or shoulder straps. Unsecured objects

may be displaced slightly. Food service may be conducted and little or no difficulty is

encountered in walking.

Moderate

Turbulence that causes changes in altitude and/or attitude occurs but the aircraft remains in positive control at all times. It usually causes

variations in indicated airspeed. Report as moderate turbulence or moderate CAT. or

Turbulence that is similar to light CHOP but of greater intensity. It causes rapid bumps or jolts

without appreciable changes in aircraft or attitude. Report as moderate CHOP.

Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are

dislodged. Food service and walking are difficult.

Severe

Turbulence that causes large abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may

be momentarily out of control. Report as severe turbulence or severe CAT.

Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are

tossed about. Food severe and walking are impossible.

Extreme Turbulence in which the aircraft in violently tossed about and is practically impossible to control. It may cause structural damage. Report as extreme turbulence or extreme CAT.

Figure 8-51 Turbulence Reporting Criteria


Icing and turbulence reports state intensities using standard terminology when possible. To lessen the chance of misinterpretation, report icing and turbulence in standard terminology. If a PIR~P stated, "...PRETTY ROUGH AT 6 500, SMOOTH AT 8,500 PA 24...," there could be many interpretations of the turbulence at 6 500 feet. A report of "light," or "severe" turbulence at 6 500 feet would have been more concise and understandable. If a pilot's description of an icing or turbulence encounter cannot readily be translated into standard terminology, the pilot's description should be transmitted verbatim.

1) Turbulence Figure 8-51 classifies each turbulence intensity according to its effect on aircraft control, structural integrity, and articles and occupants within the aircraft.

Pilots should report location(s), time (UTC), altitude, aircraft type, whether in or near clouds, intensity,, and when applicable, type (CHOP/clear air turbulence [CAT]), and duration of turbulence. Duration may be based on the time the pilot is flying between two locations or over a single location.

High-level turbulence (normally above 15 000 feet above ground level [AGL]) that is not associated with cumuliform clouds (including thunderstorms) shall be reported as CAT.

2) Icing Figure 8-52 classifies each icing intensity according to its operational effects on aircraft.

Figure 8-52 Icing Intensities, Airframe Ice Accumulation and pilot report.

Intensity Airframe Ice Accumulation Pilot Report

Trace Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not used unless encountered for an extended period of time (over 1 hr)

Location time altitude/FL aircraft type, temperature and icing intensity and type.

Light The rate of accumulation may create a problem if flight is prolonged in this environment (over 1Hr).Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used.


Moderate The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment is diversion is necessary.


Severe The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.




Pilots should report location(s), time (UTC), altitude, aircraft type, temperature, and icing intensity and type (rime, clear, or mixed). Rime ice is rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets. Clear ice is a glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled water droplets. Mixed ice is a combination of rime and clear ice.

Examples and Explanations

1) FTW UA/OV DFW 18005 /TM1803/FL095/TP PA 30/SK 036 OVC 060/070 OVC 075 /OVC ABV

The translation is:FTW / UA --PIREP from reporting station FTW OV DFW 18005 -- location is the DFW 180 radial at 5 milesTM 1803 -- time of the report is 1803FL095 -- altitude is 9 500 feet. TP PA 30 -- Type of aircraft is a PA 30 SK 036 OVC 060 070 OVC 075 OVC ABV -- Sky condition: The base of an overcast layer is at 3 600 feet with top at 6 000 feet. A second overcast layer has its base at 7 000 feet and its top is 7 500 feet. There is another overcast layer above the aircraft's altitude of 9 500 feet.

2) UA/OV KOKC 090064 /TM 1522/FL080 /TP C172 /SK SCT090-TOP UNKN /WX FV05SM HZ/TAM04/WV 24540KT/TB LGT/RM IN CLR.

This PIERP in decoded as follows: UA, 64 nautical miles east of Oklahoma City VOR at 1522UTC, flight level 8,000 feet MSL. Type of aircraft is a Cessna 172. There is a scattered cloud layer with bases at 9,000 feet MSL and unknown tops. Flight visibility is restricted to 5 statute miles due to haze. Outside air temperature is -4 degrees Celsius, wind is 245 degrees at 40 knots, light turbulence, and the aircraft is in clear skies.

3) UUA/OV ORD /TM 1235 /FL UNKN /TP B727 /TB MOD/RM LLWS +/- 20KT BLW 003 DURD RWY27L.

Urgent UA over Chicago O Hare Airport, Chicago, IL, at 1235Z. Flight level is unknown but the information is from a Boeing 727. Turbulence was moderate and on decent to runway 27 left, low-level wind shear was detected below 300 feet. Airspeed fluctuations were plus and minus 20 knots.



9. Observations and reports of volcanic activity The occurrence of pre-emption volcanic activity,, volcanic eruptions and volcanic ash cloud should be reported without delay to the associated air traffic services unit, aeronautical information services unit and meteorological watch office. The report should be made in the form of a volcanic activity report comprising the following information in the order indicated:

A. message type, VOLCANIC ACTIVITY REPORT; B. station identifier, location indicator or name of station;C. date/time of message;D. location of volcano and name if known; andE. concise description of event including, as appropriate, level of intensity of volcanic activity, occurrence of an eruption and its date and time and the existence of a volcanic ash cloud in the area together with direction of ash cloud movement and height. Note--Pre-emption volcanic activity in this context means unusual and/or increasing volcanic activity which could presage a volcanic eruption.

Example: Volcanic activity report

VOLCANIC ACTIV1TY REPORT YUSB* 231500 MT TROJEEN* VOLCANO N5605 W12652 ERUPT['D 231445 I,ARGE ASH CLOUD EXTENDING TO APPROX 30000 FEET MOVING SW

Meaning:Volcanic activity report issued by Siby/Bistock meteorological station at 1500 UTC on the 23rd of the month. Mt Trojeen volcano 56 degrees 5 minutes north 126 degrees 52 minutes west erupted at 1445 UTC on the 23rd; a large ash cloud was observed extending to approximately 30 000 feet and moving in a south-westerly direction.

10. Aerodrome warnings Aerodrome warnings shall give concise information, in plain language, of meteorological conditions which could adversely affect aircraft on the ground, including parked aircraft, and the aerodrome facilities and services. The warnings shall be issued in accordance with local arrangements to operators, aerodrome services and to others concerned, by the meteorological office designated to provide service for that aerodrome.

Aerodrome warnings should relate to the occurrence or expected occurrence of one or more of the following phenomena: • tropical cyclone;• thunderstorm;



• hail;• snow;• freezing precipitation;• hoar frost or rime;• sandstorm;• duststorm;• rising sand or dust;• strong surface wind and gusts;• squall;• frost.

11. Wind shear warnings Wind shear warnings shall give concise information of the observed or expected existence of wind shear which could adversely affect aircraft on the approach path or take-off path or during circling approach between runway level and 500 m (1 600 ft) above that level and aircraft on the runway during the landing roll or take-off run. Where local topography has been shown to produce significant wind shears at heights in excess of 500 m (1 600 ft above runway level, then 500 m (1 600 ft shall not be considered restrictive.

Wind shear conditions are normally associated with the following phenomena: • Thunderstorms, microbursts, funnel cloud (tornado or waterspout), and gust fronts; • Frontal surfaces;• Strong surface winds coupled with local topography;• Sea breeze fronts;

Mountain waves (including low-level rotors in the terminal area); • Low-level temperature inversions.

Evidence of the existence of wind shear should be derived from:A. Ground-based wind shear remote-sensing equipment, for example, Doppler radar;B. Ground-based wind shear detection equipment, for example, a system of surface wind and/or pressure sensors located in an array monitoring a specific runway or runways and associated approach and departure paths;C. Aircraft observations during the climb-out or approach phases of flight;D. Other meteorological information, for example, from appropriate sensors located on existing masts or towers in the vicinity of the aerodrome or nearby areas of high ground.

Wind shear warnings should be prepared in abbreviated plain language. Wind shear in the approach area should be reported.



Example 1"WS WRNG SURFACE WIND 320/20KMH WIND AT 60M 360/50KMH IN APCH". "WS WRNG SURFACE WIND 320/10KT WIND AT 60M 360/25KT IN APCH". Where microbursts are observed, reported by pilots or detected by ground-based wind shear detection or remote-sensing equipment, the wind shear warning should include a specific reference to microburst.

Example 2 "WS WRNG MBST APCII RWY 26'. Where information from ground-based wind shear detection or remote-sensing equipment is used to prepare a wind shear warning, the warning should, if practicable, relate to specific sections of the runway and distances along the approach path or take-off path as agreed between the meteorological authority,, the appropriate NFS authority and the operators concerned.

Example 3 "WS WRNG 30KT AIRSPEED LOSS 2NM FINAL RWY 13' or "WS WRNG 60KMH AIRSPEED LOSS 4KM FINAL RWY 13". When an aircraft report is used to prepare a wind shear warning, or to confirm a warning previously issued, the corresponding aircraft report, including the aircraft type, should be given unchanged in the warning.

Example 4 "WS WRNG B747 REPORTED MOD WS IN APCH RWY 34 AT 1510".



Documents

CAAC ATPL Study Material - flightdeckcrewing.com · CAAC ATPL Study Material. The following study material is an extract from Li Weidong (2nd edition) 2012, The Aviation Theory Course