NS2 3.4 Fronts and Storms

CHAPTER 4

FRONTS AND STORMS

Mariners have much to fear when they

are threatened by a severe storm.

A gale can strain rigging, spring seams,

bend plates, smash equipment, and tear

loose topside equipment.

The prudent mariner will maneuver to

stay clear of storms whenever possible.

An experienced mariner should be able to

see when weather disturbances are coming.

Todays radio communications provide

regular weather summaries.

The mariner at sea

will carefully plot

storm information

relative to the

vessel's position

and proposed

track.

Fronts develop when air masses of

different temperatures collide. Fronts

are weather systems that are sometimes

called waves, as in the term cold wave.

A body of air moving, resembling a

wave of the sea; usually associated

with hot or cold weather

Wave

A rapid and considerable drop in

temperature, usually affecting a

large area

Cold Wave

Usually the colder of

two air masses, being

heavier, predominates

and forces the

warmer air upward.

To be stronger or leading element

or force

Predominate

A cold front displaces the warm air

ahead of it upward.

The zone separating two air masses,

of which the cooler, denser mass is

advancing and replacing the warmer

Cold Front

A warm front moves upward over a

retreating cold air mass.

A transition zone between a mass

of warm air and the colder air it is

replacing

Warm Front

WARM

FRONT

COLD

FRONT

When a cold front overtakes a warm front it

pushes the warm air up and converges with

a cooler mass ahead of the warm front.

Cold Air

Cold Front

Warm Air

CumulonimbusUpper Air

Flow

Heavy

Precipitation

To come together

Converge

The convergent frontal mass is called an

occluded front.

Occluded Front

A composite front formed when a

cold front overtakes a warm front

and forces it aloft

Occluded Front

Frontal weather disturbances are

normally 15 - 50 miles wide for a cold

front and up to 300 miles wide for a

warm front.

The point where the cold and warm

fronts converge is frequently the center

of a low-pressure area.

Fronts develop when air masses

of different __________ collide.

a. pressure

b. size

c. speed

d. temperature

Intertropical Convergence Zone

Polar Easterlies

Polar Easterlies

Arctic Frontal Zone

Southeast Trade winds

Antarctic Frontal Zone

90N

90S

60S

30S

0

60N

30N

Northeast Trade winds

The convergence of

the northeast trade

winds of the

Northern

Hemisphere

and the

southeast

trade winds of

the Southern

Hemisphere

cause a band of

unstable weather

called the Intertropical

Convergence Zone.

90N

90S

60N

30N

0

60S

30S


Polar Easterlies

Polar Easterlies

Arctic Frontal Zone




Situated or occurring between the

tropic of Cancer and the tropic of

Capricorn; band of unstable weather

encircling the Earth

Intertropical Convergence Zone(ITCZ)

The ITCZ is a storm development area

that frequently breeds squalls.

A sudden, violent windstorm, often

accompanied by intense rain, snow,

or sleet

Squall

The Arctic Frontal

Zone develops

between the

arctic air of the

far north and

the polar

maritime air of

the North Atlantic

and Pacific Oceans.

90N

90S

60N

30N

0

60S

30S


Polar Easterlies

Polar Easterlies

Arctic Frontal Zone




Located at or near the North Pole

and pertaining to the division

between dissimilar air masses

Arctic Frontal Zone

The Polar Frontal Zone

is formed by the

convergence of

the air that

flows toward

the equator

from the Polar

Easterlies and

the Prevailing

Westerlies (the

temperate zones).

90N

90S

60N

30N

0

60S

30S


Polar Easterlies

Polar Easterlies

Arctic Frontal Zone




Polar Frontal Zone

Polar Frontal Zone

A variable frontal zone of middle

latitudes separating air masses of

polar and tropical regions

Polar Frontal Zone

Moderate in respect to temperature;

not subject to prolonged extremes

of hot or cold weather

Temperate

The three primary frontal zones are the

Intertropical Convergence Zone, the

Arctic Frontal Zone, and the _________

Frontal Zone.

a. Antarctic

b. Occluded

c. Polar

d. Subtropical

You first notice a cold front when the

sky darkens to the north and west.

Soon thereafter, the ceiling lowers and

rain begins.

A rapidly moving

cold front may

move as much as

700 miles in one

day.

Passage of a cold front is usually

marked by:

Wind shift

Drop in temperature

Rise in pressure

Rapid clearing

Squall lines often

precede a cold

front. They are often

violent, causing

flash floods from

downpours,

cloudbursts, and

extremely turbulent

winds.

What type of clouds often precede a cold

front?

a. Cirrus

b. Cumulonimbus

c. Nimbostratus

d. Stratus

Cirrus clouds in parallel precede a

warm front, followed by cirrostratus,

altostratus, nimbostratus, and finally

stratus clouds.

Visibility is poor in advance of a warm

front. Frequently fog forms, and steady

rain or drizzle prevails. Thunderstorms

may develop ahead of a warm front.

Passage of a warm front is usually

marked by:

Wind shift

Rise in temperature

Pressure remains steady or gradually

drops

Gradual clearing

Warm fronts normally move less than

15 miles per hour. Cloud sequences may

begin 48 hours in advance and occur

1,000 miles in advance of the front itself.

A warm front will be preceded by what

type of clouds?

a. Cirrus

b. Cumulus

c. Nimbus

d. Stratus

An occluded front is an unstable frontal

cyclonic rotation with a rapidly moving

cold front.

In a cold front type of occlusion, the cold

front that remains on the surface is called

the occluded front and the warm front that

is raised aloft is called the upper front.

A warm front raised aloft by a cold

front or a cold front raised aloft by

a warm front

Upper Front

Occlusions of this type:

Occur on eastern portions of continents

Have heavy frontal precipitation with

thunderstorms

Are of less intensity than cold fronts

In a warm front type of occlusion, the warm

front that remains on the surface is called

the occluded front and the cold front that

is raised aloft is called the upper front.

Cold Front

(Fast-moving)

Warm Front

(Slow-moving)

Warm front occlusion

Cold Air

Cold front aloftWarm Air

Cool Air

Occlusions of this type:

Occur chiefly in the Pacific Northwest

Cause severe icing and precipitation

With occluded fronts, the front that is

raised or lifted is called the ________

front.

a. Dominate

b. Occluded

c. Shear

d. Upper

Thunderstorms occur within clouds with

vertical development, such as cumulus

and cumulonimbus. They are of short

duration and difficult to forecast.

A transient storm of lightning and

thunder, usually with rain and

gusty winds, sometimes with hail

or tornadoes

Thunderstorm

The first stage of a

thunderstorm is the

cumulus stage

characterized by an

updraft of warm

moist air into the

atmosphere, clouds

growing taller and

taller.

The second stage,

called the mature

stage of

thunderstorm

development, is

characterized by

both updrafts and

downdrafts within

the storm-producing

cloud. Rain drops

and hail form and

begin to fall.

The final stage is

called the

dissipating or anvil

stage. The entire

lower portion of the

cloud becomes a

downdraft and high

winds flatten the top

of the cloud. Rain

falls heavily, but the

storm dissipates in

a short time.

To scatter in various directions;

disperse; dispel

Dissipate

A cloud with a flat top, shaped like

an anvil

Anvil

There are many weather phenomena

within thunderstorms. Rain is found in

all thunderstorms. Hail and snow may

also form and fall.

Something that is impressive or

extraordinary

Phenomena

A thunderstorm is most turbulent in

the area of heaviest precipitation.

Icing will often occur just above the

freezing level, making this a very

hazardous area for aircraft.

Being in a state of agitation or

tumult; disturbed

Turbulent

Thunderstorms usually occur with what

types of clouds?

a. Cirrus and Cirrostratus

b. Cumulus and cumulonimbus

c. Nimbus and Nimbostratus

d. Stratus and Cirrostratus

The leading gust of wind, sometimes

called a microburst, is one of a

thunderstorms dangers.

An intense, localized downdraft

of air that spreads on the ground,

causing rapid changes in wind

direction and speed, a localized

downburst

Microburst

The speed of the first gust is usually the

highest and can blow in any direction, even

opposite of the wind pushing the storm.

Such conditions can cause wind shear.

A condition, dangerous to aircraft,

in which the speed or direction of

the wind changes abruptly

Wind Shear

Surging air currents

in the thunderhead

cloud create static

electricity, the

source of lightning.

A brilliant electric spark discharge

in the atmosphere, occurring within

a thundercloud, between clouds, or

between clouds and the ground

Lightning

The process is not completely understood.

Positive charges develop near the top of the

cloud, and negative particles accumulate in

the lower reaches. An electrical discharge

occurs when the strength of the charges

overcomes the resistance.

Lightning may flash within a cloud.

Lightning may jump from cloud to cloud.

Lightning may jump from cloud to

ground or ground to cloud.

Lightning occurs in two steps:

A leader of electrified (ionized) air runs

between two oppositely charged

regions

The second stroke is the one you see,

and causes the thunder when the

circuit is completed.

Lightning generates terrific

heat, causing an explosive

expansion of glowing hot

air and producing the

audible thunder.

Satellite Antenna Dish

Brush Fire

Burns

Lightning follows the shortest route

between a cloud and ground. High points

are most likely to be struck. Do not stand

under trees during a thunderstorm.

Lightning also follows

the easiest route to

ground after striking.

It is very unwise

to be on or near

bodies of water

during a

thunderstorm.

Mountainous areas,

especially with

crevices or rushing

mountain streams

should be avoided

during

thunderstorms.

A crack forming an opening; cleft;

rift; fissure

Crevice

A fundamental rule for pilots is never to

fly under or through a

thunderstorm. But if

unavoidable, it should

be penetrated at

1/3 its height.

A gust in a thunderstorm that blows in

opposition to the surface wind can result

in _________.

a. a tornado

b. an occluded front

c. squalls

d. wind shear

The most intense and violent of

localized storms is the tornado.

A localized, violently destructive

windstorm occurring over land,

especially in the Middle West, and

characterized by a long, funnel

shaped cloud extending to the

ground and made visible by

condensation and debris

Tornado

Tornadoes are very small in diameter,

usually 300 to 400 feet; but may continue

on an erratic path for more than 100 miles.

Winds in the vortex may exceed 300 mph.

Vortex

A whirling mass of air in the form of

a visible column or spiral

Vortex

The speed of a tornado moving over the

Earth may be 25 - 40 mph. The duration

at any given spot may be only seconds,

but the devastation can be almost total.

A tornado forms as a funnel cloud on

the forward edge of a fully developed

cumulonimbus cloud. When the funnel

touches the ground it is called a

tornado.

If a funnel forms over water, it is called

a waterspout. It is laden with mist and

spray.

A dust devil is a small whirlwind,

common in dry regions on hot, calm

afternoons made visible by dust, debris,

and sand it picks up from the ground.

1981 - 1990 F1 through F5 Tornados

The Midwestern United States is the

most tornado-ravaged area of the world.

The extreme low pressure in the vortex

of a tornado causes homes to explode

outward from the normal pressure of

air trapped inside.

Where are tornadoes most common?

a. Doldrums

b. Equator

c. Polar Frontal Zone

d. Temperate zone

Tropical cyclones are subdivided into

three categories:

Tropical depression maximum wind

less than 34 knots

Tropical storm winds of 34 - 63

knots

Hurricane or typhoon winds of 64

knots and up

A large scale atmospheric wind-and-

pressure system characterized by low

pressure at its center and by circular

wind motion, counterclockwise in the

Northern Hemisphere, and clockwise in

the Southern Hemisphere

Cyclone

Large tropical

cyclones occur

in many places

in the world and

are called by

various names.

Hurricanes in the West Indies and on

the International Date Line, Typhoons

off China, Willy-willies off the west

coast of Australia, and Baguios off the

Philippines.

Baguios

Typhoon

Willy-willies

Cyclone

HurricaneHurricane

Cyclone

North

Atlantic Ocean

North

Pacific Ocean

South

Pacific Ocean

South

Atlantic OceanIndian

Ocean

A violent, tropical, cyclonic storm

of the western North Atlantic,

having wind speeds of or in excess

of 64 knots (74 mph)

Hurricane

A tropical cyclone or hurricane of

the western Pacific area and the

China seas

Typhoon

A severe tropical typhoon off

Australia

Willy-willies

A severe tropical typhoon off the

Philippines

Baguios

ALBERTO

BERYL

CHRIS

DEBBY

ERNESTO

FLORENCE

GORDON. . .

Today, hurricanes and typhoons are

given alternating women's and men's

names. Before 1978, all of these

storms were named after women.

The velocities of hurricanes are

much less than tornadoes, but their

destruction covers hundreds of miles

and last much longer. It is the most

destructive of all weather phenomena.

Hurricanes and typhoons were named

after women only until what year?

a. 1964

b. 1974

c. 1978

d. 1988

The birth of a

hurricane often

occurs near the

equator. They

never occur

right on the

equator because

the twisting

Coriolis forces

are not there.

Hurricanes:

Vary in diameter from 60 - 1,000 miles

Have moderate winds on the outside

and velocities as high as 175 kts

(200 mph) toward the center

At the center of a hurricane is the eye

of the storm that averages 14 miles in

diameter. This area is calm, with light

winds and clear or moderately clear

skies with some drizzle.

Eye of

The Storm

The approximate circular region

of relatively light winds and fair

weather found at the center of a

hurricane

Eye

The Atlantic hurricane starts

as a tropical low, grows into a storm,

and matures into a hurricane.

When it curves

to the northeast it

comes over cooler

waters and cooler

air, reduces internal

action and dissipates,

eventually ending up as a gale or storm

over the North Atlantic or North Sea.

Winds increase from the outer limits to

the edge of the eye

Temperature rises and humidity falls

at the center

Precipitation is heaviest in the right

front quadrant

One quarter of a circle; an arc of

90 degrees

Quadrant

Hurricanes are usually associated with

great wind-caused tides called storm

surges that inundate the land areas and

cause more damage than the wind or rain.

To flood; cover or overspread with

water; deluge

Inundate

Hurricanes are born in what type of air

mass?

a. Cold and dry

b. Cold and moist

c. Hot and dry

d. Hot and moist

Hurricanes occur most frequently in

September and October but can happen

anytime from June to December. Heavy

rains and tidal flooding are a danger.

With less frequency, but often with

greater violence, are hurricanes that

originate in the Gulf of Mexico. They

can wreak havoc throughout the Gulf

Coast and Mississippi Valley.

Tropical

Cyclone

Track

When a typhoon veers into the Asian

continent, it is usually accompanied by

significant storm surge.

Just as a hurricane may move into the

Gulf of Mexico, a typhoon may sweep

south of Indonesia into the Bay of Bengal

and then the coast of southern Asia.

Bay of

Bengal

In probably the greatest natural catastrophe

of history, a typhoon swept over the Bay of

Bengal in 1737. The storm pushed a 40-foot

surge of water inland, killing 300,000.

A sudden and widespread disaster

Catastrophe

A hurricane hit Galveston, Texas

in 1900, killing 6,000.

A hurricane hit New England in 1938,

killing 600 and causing damage in

excess of $250 million.

The boardwalk at Atlantic City, New Jersey

has been swept away several times.

The city of Belize was totally destroyed

by a hurricane in the late 1960s.

One of the strongest hurricanes ever recorded

in the Western Hemisphere was Hurricane

Gilbert that hit the Yucatan Peninsula in 1988,

killing 500 and rendering 500,000 homeless.

One of Floridas greatest disasters

happened in 1992 when Hurricane

Andrew crossed the Florida Peninsula.

Hurricane Katrina caused major damage

to the New Orleans area. Levies broke

that caused major flooding of the city.

Hurricane

Katrina

Devastation

of Hurricane

Katrina

Cyclonic winds rotate counterclockwise

in the Northern Hemisphere and

clockwise in the Southern Hemisphere.

Southern Hemisphere

Northern Hemisphere

DANGEROUS

SEMI-CIRCLE

NAVIGABLE

SEMI-CIRCLE

Winds in the right semicircle draw ships

into the path of the storm. Winds in the

left semicircle tend to drive the ship out

of the path of the storm.

navigable

semicircledangerous

semicircle

storm

direction

Maneuvering a vessel in a hurricane

consists of determining whether she is in,

or approaching, the dangerous semicircle,

and if she is, finding the best method of

working out of the undesirable position.

If you face in the same direction a

hurricane in the Northern Hemisphere is

moving, winds in the left semicircle are

called the navigable semicircle.

a. True

b. False

Flags and pennants

hoisted at the National

Weather Service and

other shore stations

indicate the presence

or forecast presence

of unfavorable winds.

One red pennant displayed by day,

and a red light over a white light at

night, indicate winds of up to 33 knots

(38 mph) and sea conditions dangerous

to small craft are forecast.

SMALL

CRAFT

WARNING

Two red pennants by day, and a white

light above a red light at night, indicate

winds ranging from 34-47 knots (39-54

mph) are forecast.

GALE

WARNING

A single square red flag with a black center

displayed by day, and two red lights at

night, indicate that winds of48 knots (55

mph) and above are forecast.

STORM

WARNING

Two square red flags with black centers

by day and a white light between two

red lights at night, indicate winds 64

knots (74 mph) or greater are forecast.

HURRICANE

WARNING

Which storm warning signal is composed

of a white light above a red light at night?

a. Gale

b. Hurricane

c. Small craft

d. Storm

The U.S. Hurricane

Warning System

was set up in 1938.

Reconnaissance airplanes equipped

with radar and weather instruments are

sent to scout suspected storm areas

and to monitor hurricanes.

A general examination or survey

of a region

Reconnaissance

In recent years,

weather satellites

supplemented by

reconnaissance

aircraft are used

to supply data

on hurricanes.

Bulletins are issued every couple of

hours to warn all who are in danger to

prepare for the storm by securing their

property and to evacuate.

In what year was the U.S. Hurricane

Warning System set up?

a. 1938

b. 1947

c. 1966

d. 1974

Q.1. What are weather fronts?

A.1. The boundary between air

masses with different

characteristics, e.g., moisture,

temperature, etc.

Q.1. What are weather fronts?

Q.2. What causes fronts to form

wave-like patterns?

A.2. The friction of the ground and

circular motion of the air in

front of and behind the fronts

Q.2. What causes fronts to form

wave-like patterns?

Q.3. How far may a frontal wave

extend?

A.3. For hundreds of miles along

the surface

Q.3. How far may a frontal wave

extend?

Q.4. How far do frontal weather

disturbances extend for cold

and warm fronts?

A.4. Generally from 15 - 50 miles

wide in front of a cold front,

and up to 300 miles wide for

a warm front

Q.4. How far do frontal weather

disturbances extend for cold

and warm fronts?

Q.5. What are the primary frontal

zones around the world?

A.5. a. The Intertropical

Convergence Zone

b. The Arctic Frontal Zone

c. The Polar Frontal Zone

Q.5. What are the primary frontal

zones around the world?

Q.6. What forms the Intertropical

Convergence Zone (ITCZ)?

A.6. The convergence of the trade

winds from the Northern and

Southern Hemispheres

Q.6. What forms the Intertropical

Convergence Zone (ITCZ)?

Q.7. What happens to the Arctic

Frontal Zone during the

summer?

A.7. It moves to the north and

disappears

Q.7. What happens to the Arctic

Frontal Zone during the

summer?

Q.8. What is the significance of the

Polar Frontal Zone?

A.8. It has the greatest influence on

the weather in the temperate

zone.

Q.8. What is the significance of the

Polar Frontal Zone?

Q.9. What kind of weather is

produced in front of a fast-

moving cold front?

A.9. Violent thunderstorms and rain

Q.9. What kind of weather is

produced in front of a fast-

moving cold front?

Q.10. Where do tornadoes develop?

A.10. Generally within a squall line

or severe thunderstorm in

front of a fast-moving cold

front

Q.10. Where do tornadoes develop?

Q.11. What is a tropical cyclone?

A.11. A low pressure circulation

that forms in the tropics

Q.11. What is a tropical cyclone?

Q.12. What are the three categories

of tropical cyclones?

A.12. a. Tropical depressions

b. Tropical storms

c. Hurricanes (or typhoons)

Q.12. What are the three categories

of tropical cyclones?

Q.13. Where do hurricanes form?

A.13. Over the tropical water of the

Atlantic and the Pacific (out to

the International Date Line)

Q.13. Where do hurricanes form?

Q.14. How far in advance of a

hurricane can the effects be

seen?

A.14. Clouds, weather and swells

can be seen up to 1,000 miles

in advance.

Q.14. How far in advance of a

hurricane can the effects be

seen?

Q.15. When do most hurricanes

occur?

A.15. June to December is

hurricane season, but most

hurricanes occur in

September and October.

Q.15. When do most hurricanes

occur?

Q.16. Which is the most dangerous

semicircle of a hurricane?

A.16. The right semicircle (when

facing in the direction the

hurricane is moving) because

the winds tend to draw ships

toward the worst weather

Q.16. Which is the most dangerous

semicircle of a hurricane?

Q.17. What warnings are displayed

to indicate the presence or

forecast of unfavorable or

dangerous winds?

A.17. Small craft, gale, storm, and

hurricane warnings

Q.17. What warnings are displayed

to indicate the presence or

forecast of unfavorable or

dangerous winds?

Q.18. What countries are associated

with (a) typhoons and

(b) baguios?

A.18. a. China

b. The Philippines

Q.18. What countries are associated

with (a) typhoons and

(b) baguios?

Q.19. What information on a storm

does a weather forecast

consist of?

A.19. Probable path, intensity, and

timely warning to all who may

be in danger

Q.19. What information on a storm

does a weather forecast

consist of?

Education

NS2 3.4 Fronts and Storms