U N I V E R S I T Y O F K E N T U C K Y — C O L L E G E O F A G R I C U L T U R E

C O O P E R A T I V E E X T E N S I O N S E R V I C E

A G R I C U L T U R E & N AT U R A L R E S O U R C E S • FA M I LY & C O N S U M E R S C I E N C E S4 - H / Y O U T H D E V E L O P M E N T • C O M M U N I T Y & E C O N O M I C D E V E L O P M E N T

4DA-03PA

Weather VariablesKentucky 4-H Weather Project

Unit IIITom Priddy, Extension Agricultural Meteorologist

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IntroductionIn this unit of the 4-H weather

project, we will be looking at and de-scribing how to measure thedifferent elements that make theweather. These elements, such as airtemperature, wind speed and direc-tion, and precipitation, are normallycalled the weather variables becauseeach element changes with time, yetare all related. We’ll look at these re-lationships and forecasting in detail inUnit IV.

First, let’s learn about temperatureas a weather variable.

Objectives• Learn how temperature changes

affect other weather conditions.• Learn how wind patterns affect

the weather.• Learn why humidity is one of the

weather variables.

Activities• Make a weather station.• Give a weather demonstration.• Exhibit a weather station at the

county fair.• Submit project records and

weather observations.

ContentsIntroduction .................................................................................................. 2Objectives .................................................................................................... 2Activities ....................................................................................................... 2

TemperatureWhy Kentucky Temperatures Vary ................................................................ 3Activity: Making an Accurate Rain Gauge .................................................... 3

WindsMaking a Weather Vane ............................................................................... 4Thar’ She Blows ........................................................................................... 4Where the Winds Come From ...................................................................... 4Why Our Winds Blow from West to East ...................................................... 5Kentucky Breezes and Winds ....................................................................... 6How Fast Is the Wind Blowing ...................................................................... 6Experiment: Making a Cup Anemometer ...................................................... 6The Beaufort Scale for Measuring Wind Speed ........................................... 7

HumidityUnderstanding Water Vapor in the Atmosphere ........................................... 8100% Relative Humidity or Saturated Air? ................................................... 8The Hair Hygrometer .................................................................................... 8Building a Hair Hygrometer .......................................................................... 9

Summing UpWhat’s Next? ................................................................................................ 9Talks & Demonstrations ................................................................................ 9Citizenship & Leadership Activities .............................................................. 9

Observation Sheets .................................................................................... 10Weather Variables Record Sheet ............................................................... 12

Weather Variables

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funnel

candle wax

plastic disc

tin can

One of the first questions we askabout the weather is, “What is the tem-perature?” In Unit I, you learned howto keep temperature readings, and inUnit II, you continued to keep thosereadings. But just what do these read-ings mean? Temperature affects allother weather conditions. Withoutchanges in temperature, there wouldbe no changes in pressure, wind, orhumidity.

For this project, you can use thesame thermometer you used in UnitsI and II. If you need a new thermom-eter, many feed stores and farm-re-lated businesses give them away free,or you may want to purchase an inex-pensive one. Put the thermometer inyour weather shelter where it will beout of direct sunlight and yet will haveair circulating around it.

Why KentuckyTemperatures Vary

Have you ever participated in4-H events with 4-H’ers from adifferent part of the state? In Kentucky,4-H’ers compete on local, county, area,and state levels. Perhaps when youwent to 4-H camp or attended Ken-tucky 4-H Week in Lexington, you hadthe opportunity to talk to membersfrom many different 4-H areas. Didyou know that their weather may dif-fer from yours? Watch the TV weatherbrief for one week and record the dailyhigh temperature near your locationand one other location across thestate. Discuss these differences in thetemperature readings. One reasontemperature varies throughout Ken-tucky is that our latitude varies. The far-ther one travels north, the cooler thetemperature will be.

Another major reason for air tem-perature differences in Kentucky is thewide variety of terrains. In the BlueGrass and Fort Harrod areas, the landis fairly flat. In comparison, the east-ern portion of the state has many hills

and mountains. These differences inthe terrain can readily influenceweather changes. The AppalachianMountains are located in the North-east, Quicksand, and Wilderness Trailareas. As weather moves from thewestern sections of Kentucky, the airmust rise to travel across the moun-tains. As the air attains a higher alti-tude, the temperatures cool. Not onlydoes this produce a temperaturechange but also helps to create rainfall.

Activity: Making anAccurate RainGauge

In Unit II you learned how to use asimple rain gauge. For this unit, you willimprove your rain gauge to make itmore accurate. First, check your old raingauge. Make sure the paint has notchipped and the can will not rust. Sec-ondly, cut a circle of plastic foam thatwill fit inside the can snugly. Now,make a hole in the middle of the plas-tic large enough for the end of the fun-nel to be placed. The funnel must bethe same diameter (distance acrossthe top) as the can. Why is this so?(Hint: Compare the area of the top ofthe funnel to that of the can.) Put thefunnel in place. By adding the plastic

Temperatureand the funnel, you have made a shieldthat will prevent evaporation and helpyou to make more accurate readings.

Now, you are ready to take read-ings. Measure the precipitation with aplastic ruler just as you did before. Re-member to pour out the precipitationafter each reading so your next read-ing will be accurate. (You will be keep-ing records of the precipitation forthree months.) A general rule is tomeasure precipitation to the nearesttenth of an inch. (What other units ofmeasure could you use? Hint: MM).Comparing your reading with theweather news will help you learn tobe more accurate. You may wish todevise a holder for your rain gaugeso it will not blow over. Keep your raingauge on top of your weather station(see Figure 1).

Figure 1. Advanced rain gauge.

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Figure 2. Weather vane.

Long before weather vanes orwind-measuring instruments hadbeen thought of, early weather watch-ers recognized that wind direction wasimportant. They didn’t understandwhy, but they knew that wind from onedirection generally brought fair skieswhile wind from another directionbrought rain. So they watched the treessway for a sign of the wind direction.

Making a WeatherVane

Today we have better ways of de-termining wind direction. A sensitiveweather vane can be constructedfairly easily. You will need a piece ofwood for an arrow about 12" long, ½"thick, and 3" wide; a mounting stick; a¾" by 1' board; a nail or screw for at-taching the arrow to the mountingstick; and two washers (see Figure 2).

Draw an arrow like the one shown.Then, cut the arrow out of the wood.You may ask your leader to supervise.Find the point where the arrow isequally balanced by steadying it onyour finger. This is the balance point.Drill a hole at that point through theshaft of the arrow. Paint the weathervane white to match your weather sta-tion. Now, you are ready to attach theweather vane to your weather station.Be sure one side of the mounting stickfaces north. Label the stick with thecompass points—north, east, south,and west—ensuring that north on thestick points to the north.

Thar’ She BlowsAs you observe the wind for

direction, you may start to notice aspecial wind pattern. Here are a fewpatterns that apply to many parts ofthe United States. See if it holds trueto where you live.

• Winds from the north, northwest,and west generally bring dry andcooler weather. They blow fromcooler masses of air to the northand drier masses of air to the west.

• Winds from the west, southwest,and south bring fair and warmerweather. They blow from warmerlands.

• Winds from the east, southeast,and northeast generally bringrain. They blow in from the ocean.

In Kentucky, the most commonwind direction is from the south. How-ever, during February and March,northwesterly winds are common. Forthe next three months, you will be re-cording the wind direction.

Where the WindsCome From

Wind is caused by air moving froma high pressure to a low pressure area.Whether the wind is a small gust play-fully whirling up dust in the cornfieldor a great wind of tornado force, thecause is always the same. Air that isunder pressure is trying to escape orbalance itself and heads for thenearest area of lower pressure. If thedifference in the high and lowpressure is great, the wind will bestrong. If the difference is slight, thewind will be light.

The sun sets the stage for the world’sgreat winds. At the equator, where thesun shines constantly each day, warmair rises in a mighty stream. The con-

stant heat forms a low pressure beltof rising air known as the Doldrums.

According to Figure 3, as air risesfrom the Doldrums, it cools and driftstoward the poles. Some of it falls in theHorse Latitudes, around the 30° lati-tude, and piles up to create a belt ofhigh pressure. The constant pressureof the Doldrums and the Horse Lati-tudes makes these regions of calm orvery light winds. But in between them,air is on the move. Rushing from highpressure to low pressure, the air flowsback toward the equator as the strongand steady northeasterly Trade Winds.

Some of the air that rises from theequator continues on to the poles.There it sinks, becomes compressed,and rushes out toward the 60° latitude.These icy blasts from the poles arethe Polar Easterlies. If these icywinds dip into the middle latitudes,they can bring snow to Florida. Therest of the winds, between the HorseLatitudes and the Polar Easterlies, areblown back toward the poles. Theseare called the Prevailing Westerlies.They control the major wind currentsfor the United States and Europe.

Equator Doldrums are caused bywarm air rushing over the equatorarea. Sailing ships often went on fordays and days in this region withoutso much as a breeze of wind to fill

Winds

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Figure 3. Earth’s wind circulationpattern.

their sails. Heavy rainfall, summer ty-phoons, and hurricanes are typical forthis region.

Trade Winds are so named be-cause many years ago sailingvessels traveled the seas carryingcargo, and the winds of this regionaided them in transporting their goodsto other trade centers. The skies aremostly clear in this area.

The Horse Latitudes are a verycalm, warm region. Winds there arevery weak. The skies there are clear.Sailing ships carrying horses to thenew world were often delayed in thisarea because of the lack of wind. Thestory goes that when food for the ani-mals ran out, the animals starved todeath and were thrown overboard.

The Prevailing Westerlies controlthe major air flows in the UnitedStates. If interference from polar frontsdid not occur, the United States wouldhave fair weather with clear skies andoccasional rains.

Why Our Winds Blowfrom West to East

What would happen if the earthwere not rotating? We already knowthat warm air rises. If the earthstopped spinning, the warm air wouldrise to the poles. There, the warm air

would cool down and sink. The pres-sure of this sinking cool air would forcesurface air toward the equator at aneven speed. This could drastically al-ter our normal weather patterns.

However, we know the earth ro-tates. It takes 24 hours for the globeto make one complete turn. At its wid-est point, the equator, the earth is ap-proximately 25,000 miles around. Theearth rotates eastward at 1,000 milesper hour. At locations north or southof the equator, the earth becomes

fewer miles around. The equator mustmove faster than the poles to main-tain the one rotation per 24 hour mo-tion. Let’s see how these differentrates of rotation change the nature ofour winds.

You will need an old phonographrecord, a turntable, and a piece ofchalk. Place the record on the turn-table spindle. Now, pretend the cen-ter hole is the North Pole and the outeredge of the record is the equator. Takethe phonograph record and rotate itcounter-clockwise on the spindle. Thisrepresents the way the earth turns asseen from the North Pole. With a pieceof chalk, try to draw a straight line fromthe spindle to the edge of the recordwhile the record is in motion. Whathappens? All you can draw is a curve,as in Figure 4.

This is called the Coriolis Effect.Our winds move just like the chalk line.Winds coming in from the north curveto the right. From south, the windscurve to the left.

Kentucky Breezesand Winds

Kentucky has a number of lake andmountain areas. The varied tempera-tures of these geographical locationscan affect the air current of theseplaces. For example, there is almost

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Figure 4. The Coriolis Effect.

always a breeze at Kentucky Lake. Doyou know why? It blows one way dur-ing the day and the opposite way atnight. During the day, the land heatsfaster than the water. Cooler, heavierair from the water blows toward theland. At night, the land cools fasterthan the water. The cool, heavier landair blows toward the lake.

Have you ever been to the top ofBlack Mountain, Kentucky’s highestpeak? If you have, you may have won-dered about another special set ofwinds. During the day, these windsblow up the mountain. At night, theycome whistling down. Can you figureout why? (Hint: Warm air rises upslopeduring the day; at night, cool air sinks.)

How Fast Is theWind Blowing?

The speed of the wind tells us howgreat the pressure difference is be-tween two masses of air. To measurewind speed, we can use a scale setup by Admiral Beaufort of the BritishNavy in 1805. (See the Beaufort Scalefor Measuring Wind Speed on the nextpage.) However, to make our weatherstation more complete, we can buildan anemometer to measure windspeed.

Experiment: Makinga Cup Anemometer

You will need either three aluminumfunnels (2½" in diameter) or threesmall gelatin molds, three 3/16" dowelrods (17" long), one metal (or plastic)

pencil or pen cap, one metal lid 1¾"to 2" in diameter, one small washer3/8" in diameter, one 3" nail, waterproofheavy-duty glue, paint, and liquid sol-der (see Figure 5).

Wind speed is often measured bya cup anemometer. There are manyways to build an anemometer of thiskind. Cups can be made using eitherfunnels or gelatin molds. If small fun-nels are used, it might be necessary

to close the ends where the spoutswere cut off with liquid solder. Con-struction details for the rest of the as-sembly are about the same regardlessof the cups used.

1. Punch holes on opposite sidesof the cups so that dowel rods fittightly through them. Then, po-sition as shown in theillustration and fasten withwaterproof glue.

2. Make the hub assembly by us-ing a small bottle lid about1½" to 2" in diameter. The lidfrom an ink bottle or other smalljar will work very well. Punch ordrill three equally spaced holesin the rim of the lid to receive thecup spokes. Punch another holein the center of the top. Glue aballpoint pen cap into this holeas shown.

3. Glue a small washer over theopening of the pen cap.

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TTTTThe Beaufhe Beaufhe Beaufhe Beaufhe Beaufororororort Scale ft Scale ft Scale ft Scale ft Scale for Measuring or Measuring or Measuring or Measuring or Measuring WWWWWind Speedind Speedind Speedind Speedind SpeedDescription Speed (mph) ObservationCalm less than 1 Smoke rises straight up. Trees are still. Water is mirror calm.Light air 1-3 Smoke drifts in direction of wind. Leaves on trees move slightly.Light breeze 4-7 Wind can be felt on face. Leaves rustle.Gentle breeze 8-12 Leaves in constant motion. Light flags flap.Moderate breeze 13-18 Small branches move. Dust is stirred up.Fresh breeze 19-24 Young, leafy trees sway. Dust is stirred up in clouds. Crested wavelets on

lakes and ponds.Strong breeze 25-31 Tree boughs swing. Wind whistles through telephone wires.Moderate gale 32-38 Tree trunks swing. Difficult walking against the wind.Fresh gale 39-46 Walking requires effort. Small branches break.Strong gale 47-54 Slight damage to buildings, signs, and windows.Whole gale 55-63 Trees are blown down. Considerable damage to buildings (more often

experienced at sea).Storm 64-74 Wide damage (rare).Hurricane 75 or more Great damage, wide destruction.

Figure 5. Cup Anemometer.

4. Insert the cup spokes throughthe holes in the rim of the lid untilthe ends touch the pen cap.

5. Glue the cup spokes to the capand the underside of the washer.

6. Paint one cup and spoke adifferent color.

The anemometer can be calibratedin different ways. One way is to mountit on the handle of a broom stick orother suitable board that can be heldout a car window well above the carroof while driving along a straight

stretch of road. Have your parent orolder brother or sister drive down theroad, first at 5, then at 10, and finallyat 15 miles per hour while you countthe turns it makes in ten seconds. Mul-tiply this number by six to get the num-ber of rounds it makes per minute for5, 10, and 15 miles per hour. Unlessthe calibration is made when the windis not blowing, the procedure mustthen be repeated going at the samespeed in the reverse direction. Thenthe average of these two measure-ments will give the more accurate cali-bration. The Beaufort Scale belowmay help you to interpret the readingsyou take. You will be recording thewind speed for the next three months.

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Figure 6. Hair hygrometer.

HumidityUnderstandingWater Vapor in theAtmosphere

In the previous units, you havelearned about humidity in the air—mainly in the saturated state. Whenthe air is completely saturated, cloudsand possibly precipitation occur. Usu-ally these are the only times whenmany people are aware of moisturein the air. But even in the coldest air,moisture, in the form of water vapor,is present. If you’ve ever stripped to-bacco, you can physically feel and seethe effect of humidity in the air; if hu-midity has been high, tobacco will bein case. If humidity has been low, thetobacco leaves are brittle and not incase.

There are many terms used to de-scribe the amount of humidity in theair. Two of the most commonly usedterms are:Humidity: The amount of water va-por in the air.Relative Humidity: The percentageof water vapor the air is holding basedon the amount the air can hold at thatparticular temperature.

100% RelativeHumidity orSaturated Air?

What’s the difference between 100percent relative humidity as comparedwith saturated air? The answer: none.Air that is completely saturated has arelative humidity of 100 percent andcannot hold any more water vapor atthat temperature. How does the wa-ter fall out of the air? It takes one oftwo processes for this to occur:

1. By cooling the saturated air.2. By adding more water.

As moist air rises, it slowly cools.As the temperature drops, the rela-tive amount of moisture the air canhold decreases to a point where any

further cooling would cause conden-sation. The air is said to be completelysaturated, and the relative humidity ofthis air is 100 percent. Any further cool-ing would cause precipitation.

During the summer months, wecan see this occur almost every day.In the morning, the puffy cumulusclouds dot the sky. By midday, sun-shine heats the earth’s surface caus-ing the air near the surface to warmand begin to rise. The cumulus cloudsbuild vertically into towering cumulusand often into cumulonimbus—the truethunderhead (see clouds in Unit II).

The second process can occur asfollows: if the air is near saturation anda southerly wind is pumping moremoist warm air into the region, the airwill become saturated, and precipita-tion will occur.

The HairHygrometer

What happens to your hair whenyou go swimming? Of course it getswet, but it also stretches. Now, whathappens after you blow-dry your hair?You get the frizzies! This very simpleprocess of hair contracting and ex-

panding, depending on the humidity,is the principle by which a very simplebut accurate hygrometer is con-structed. This word comes from Latinand means to measure water.

Invented in the mid-17th century,hygrometers indicate how damp, orhumid, the air is. Earlier, simpler hy-drometers contained a substancethat changed drast ical ly withchanges in the amount of moisturein the air. Hair is such a substance.Can you think of other substancesthat are similarly affected?

As the air becomes more humid, thelong strand of human hair in the hy-grometer, shown in Figure 6,stretches. This causes the suspendedpenny to slowly drop, and the needleturns, indicating the relative amountof moisture in the air.

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Summing Up

Building aHygrometer

To build your own hygrometer, youwill need one shoe box, one hair (longstrand), one paper clip, transparenttape, one match stick or broom bristle,one file card (3" x 5"), one needle, andone penny.

Construct your hygrometer asshown in Figure 6. If the pointer doesnot move very much, the needle isprobably stuck. What would you do tohelp the needle move more easily?(Hint: reduce friction.)

If, after building a hair hygrometer,you keep it in your house, what hu-midity will you measure? Is humiditydifferent inside your home as com-pared to outside? If you want to mea-sure relative humidity outside, whereshould you keep your hygrometer?(Hint: Did you build a weather shelter?)

YOU DID IT! You have made a ba-sic weather station! You have learnedhow to use the basic tools of a me-teorologist: a rain gauge, a barometer,a thermometer, a weather vane, ananemometer, and the Beaufort Scale.Now that you have an understandingof these tools and what they indicate,you can make observations of

weather for your local area with a fairamount of accuracy. Keep records forthree months to observe the weathertrends.

Give demonstrations and talksshowing how these instruments work.Visit a local weather center and seejust how predictions are made for thenews media.

Exhibit your weather station and in-struments at the county fair. Include atleast one month’s observation withyour exhibit.

Be sure to submit your record book,including the project story, weatherobservations, photo sheet, and recordsheets.

What’s Next?In the next unit, you will learn how

to read weather maps, how to give aweather forecast, and how to qualifyas a Storm Spotter’s Guide for your lo-cal area.

Talks &Demonstrations

Giving a talk or demonstration is anexcellent experience. First, it helps youlearn to organize a helpful, logicalpiece of information to share withsomeone else. Then, it gives you ex-perience in speaking in front of a group.This can be a small or large group. Italso helps your audience by teachingthem about weather—possibly givingthem information that could save theirlives. So as you go through this project,be thinking about what you would liketo share with a group.

You may want to do a demonstra-tion on how to build some of theweather instruments that you put inyour weather station. Or you may wantto help your audience learn aboutweather variables so they can be pre-pared to predict the weather for them-selves.

Citizenship &LeadershipActivities

1. Help your leader organize aweather workshop for another4-H club or any other appropri-ate group.

2. Prepare posters showingKentucky’s wind or otherweather patterns. Use your 3-month records to develop theseposters. Display them in yourschool or bank or other publicplace.

3. Serve as a leader for a youngergroup of 4-H’ers. Help them withtheir weather experiments or inany way that you can be ofservice to the group.

4. Take a group to visit a weatherstation, or invite a meteorolo-gist to talk to your group oranother group about weatherinstruments.

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Weather VariablesKentucky 4-H Weather Project Unit III

Record Sheet

Name __________________________________________________ Birth Date __________ Grade _____________

Address _____________________________________________________________________________________(Street & Number/P.O. Box) (City) (Zip)

Name of Club or School _______________________________________ County __________________________

Number of Years in 4-H __________________________________________ Current Date ___________________

1. Describe the weather station you constructed.

_____________________________________________________________________________________________________

_____________________________________________________________________________________________________

2. Did you complete the weather observation chart for three months?_______________________________________

3. List the experiments you completed. _______________________________________________________________

_______________________________________________________________________________________________

4. Indicate talks and demonstrations you gave for your weather project.

Title Audience No. of People Date Award/Recognition

____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________

__________________________________________________________________________________________________

5. Indicate the leadership/citizenship activities you completed as part of this weather project.

Type of Activity Where Number of People Date

_____________________________________________________________________________________________________

_____________________________________________________________________________________________________

_______________________________________________________________________________________________________________________

6. Did you submit weather records for county competition? ______________ Award or recognition: ______________

7. On a separate sheet of paper, write about the things you have learned and done in this project. Include three tofive photographs of you working on your project.

________________________________________ ________________________________________Member’s Signature Leader’s Signature

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