Weather Elements Know basic facts and general principles of the elements of weather. 1. Identify types of clouds. 2. Identify types of air masses and fronts.

Weather Elements

Know basic facts and general principles of the elements of weather.1. Identify types of clouds.

2. Identify types of air masses and fronts.

3. Describe terrain factors that affect weather.

4. Describe types of turbulence.

5. Identify normal weather patterns.

Overview

1. Clouds

2. Air Masses and Fronts

3. Terrain Factors

4. Turbulence

5. Normal Weather Patterns

Types of Clouds

Low Clouds

• Stratus• Sheet - like cloud.• No turbulence.• May be risen fog.• Light drizzle or snow.• Close to Earth’s surface.• Can hide danger.

Low Clouds

• Stratocumulus• Rolls or global

masses.• Bulbous protrusions.• Heavy rain and snow• Varying turbulence.• Masks higher severe

cloud buildups.

Low Clouds

• Cumulonimbus• Vertical growth

group.• Top has anvil shape.• High winds, snow,

hail, rain, lightning, and tornadoes.

• Extreme turbulence.

Low Clouds

• Nimbostratus• Shapeless, low-level,

moderate precipitation.• Fog and precipitation

found beneath.• Visibility restricted.• Calm to light winds.

Middle Clouds

• Altostratus• Relatively thin.• Sun may be seen

through veil.• Ice crystals and

super-cooled water.• Light precipitation.• Poor surface

visibility.

Middle Clouds

• Altocumulus• Wavy solid clouds

with rounded outline.• Light intermittent rain

or snow.• Commonly followed

by thunderstorms.• Poor visibility and

moderate surface winds.

High Clouds

• Cirrus• Thin feathery

clouds.• No precipitation.• Sign of approaching

bad weather.

High Clouds

• Cirrostratus• Thin, resembles a

sheet or veil.• No precipitation.• Nearly transparent.• Often sign of

approaching bad weather.

High Clouds

• Cirrocumulus• Thin clouds.• Indicates high-level

instability.• Similar to cirrostratus

but they have a slightly “bumpy” appearance.

Fracto and Lenticular

• Fracto• Broken and/or

ragged.• Cumulus fractos.

• Lenticular• Lens-like shape.• Tells turbulence, visibility,

precipitation.

–

Cumulus with Vertical Growth

• Fair weather cumulus• A puffy, cottonball

appearance.• Develops from

thermal updrafts.• Flights below can be

bumpy and choppy.

Cumulus with Vertical Growth

• Vertical growth, or building cumulus• Produce strong rain

and moderate to severe turbulence.

• Very strong updrafts. • With further building

and increase in intensity, it becomes a thunderstorm.

Fog Types

Fog Types

• Radiation Fog

• Formed at night when land surfaces radiate much of the heat absorbed from the Sun back into space.

• The cool land surface cools the air near it to below the dew point and fog is formed.

• High Inversion Fog

• A low fog.• Formed by condensation of water vapor at or

near the top of cool air, which is overlain by a warmer air layer.

Fog Types

Fog Types

• Advection Fog

• Formed when wind blows moist air over a cold surface.

• When the surface cools the air to its dew point temperature, fog is formed.

• Evaporation Fog

• Also called steam fog, may occur when cold air moves over warm water.

• The water’s normal evaporation process saturates the cooler air with water vapor and the dew point is reached.

Fog Types

• Upslope Fog

• Results when wind carries moist air up to a mountain slope or sloping land.

• The air cools to its dew point as it rises and water vapor then condenses into fog.

Fog Types

Air Masses and Fronts

Air Mass

• A large body of air (usually extending over an area 1,000 or more miles across) which has generally the same temperature and moisture content within the entire mass.

Air Mass Type and Origination

Air Mass Type and Origination

• Air masses are identified by letter symbols.

• A polar air mass (P) is cold.• A tropical air mass (T) is

hot.• A maritime air mass (m)

forms over water and is humid.

• A continental air mass (c) forms over land and is dry.

Air Mass Type and Origination

• Aviators and meteorologists in the continental United States are chiefly concerned with air masses origination at two sources.

• Masses that move southward from Polar Regions.

• Masses that move northward from Tropical Regions.

Air Mass Type and Origination

• Cold air masses• Continental polar (cP)• Maritime polar (mP)• Arctic (A)

Air Mass Type and Origination

• The principle warm air mass is maritime tropic (mT)

Temperature Classification of Air Masses

• Based upon its temperature in relation to the surface over which it passes.

• A cold air mass (k) is cooler than the Earth’s surface over which it is moving.

• A warm air mass (w) is warmer than the Earth’s surface over which it is moving.

Temperature Classification of Air Masses

• Continental polar cold (cPk) - originates in the polar zone and moves south over a warm surface.

• Maritime tropical warm (mTw) - originates over the Gulf of Mexico and moves toward the north over a cold surface.

Characteristics of Air Masses

• Air masses originating in the tropical and equatorial areas move toward the northeast.

• Air masses originating in the arctic and polar area move toward the southeast.

Characteristics of Air Masses

• Cold air masses move more rapidly than warm air masses.

• The weather generally depends on the nature of a prevailing air mass or the interaction of two or more air masses.

Characteristics of Air Masses

• As an air mass moves away from its source, its original characteristics are changed because of the surface it passes over. It may:• Become warmer or colder.• Absorb or lose moisture.• Be lifted up by mountains or subside into

valleys.

Fronts

• The boundaries between air masses are called frontal zones or fronts.

• This boundary or front moves along the Earth’s surface as one air mass displaces another.• If a cold air mass replaces a warmer air mass, the

boundary is called a cold front.• If a warm air mass replaces a cold air mass, the

boundary is called a warm front.

Cold Front

Fronts

• Cold Fronts• Northwest to southeast.• Cold fronts travel very far south.• Amount of energy depends on amount of cold

air in high-pressure cell.• Formed at the junction of the high-pressure.

cold air with low-pressure warm air. • Cold air forces the warm air upward.

Fronts

• Cold Fronts• Movement depends on condition of the warm

air it collides with.• In western states, the noticeable change is shift

of wind, temperature, and blowing dust.• In southern and eastern states it causes

problems for aviators.

Fronts

• Cold Fronts• As warm air is forced upward, it cools,

condenses into clouds, creating thunderstorms.• If movement is rapid, with an abundance of

water vapor, violent weather takes place.• Squall lines develop ahead of the front.

Fronts

• Cold Fronts• Along the cold front there will be a low-

pressure cell where the weather is at its worst.• Almost any type of clouds can be found near the

cell.

• Poor visibility, low ceilings and rain in summer.

• Freezing rain and snow in winter.

Warm Front

Fronts

• Warm Fronts• Connected to a low-pressure cell, travels

northeastward.• If cell did not move, the front would dissipate.• Front slips upward over cool air and forms a

wedge.• Rises slowly which delays condensation.

Fronts

• Warm Fronts• Front is announced by cirrus clouds.• As front approaches other clouds, skies darken.• Near the frontal boundary, clouds are low,

gentle rain falls and visibility is poor.• Warm rain falling into cooler air causes fog.

Fronts

• Warm Fronts• After front passes, there is a rise in temperatures,

general clearing and change in wind direction.• In winter a warm front causes icing conditions at

low altitudes.• In northern latitudes snow may also be

produced.

Stationary Front

Fronts

• Stationary Front• When air masses stop, a stationary front

develops.• Weather can be bad for aviation along the front.• About every form of weather can be found.

Front

• Stationary Front• Toward the trailing edge of the any front there

will be a stationary-front condition.• The trailing edge stationary fronts are a great

distance from the parent cell.• As the distance become greater the front no

longer exists.

Occluded Front

Front

• Occluded Front• There is a tendency for a horizontal bend or

wave to occur along the front.• After a frontal bend starts, cold air moves ahead

of a warm front.• The cold section moves faster than the warm

section.

Front

• Occluded Front• The resulting front is called occluded or

occlusion.• Air pressure becomes less at the wave or bend

than at other points.• The weather that results is a combination of

cold and warm front weather.

Terrain Factors

Terrain Factors

• The presence of mountain ranges change the characteristics of a front.

• As air masses enter the United States the mountains cause them to rise.

• Along many seacoasts there is a breeze from the sea by day. This moist, relatively cool air rises and heats as it passes across land.

• Convectional clouds form and bring afternoon showers.

Terrain Factors

• At night the land cools and the breeze blows toward the sea.

• Wind blowing toward land formations and condensation will occur.

• The reverse can happen if the wind forces clouds downward into warmer air.

Turbulence

Turbulence

• Thermal Turbulence• Intense surface heating causes convection

currents.• More intense convection currents occur over

dark-colored ground.• Less convection currents will be over light-

colored ground.• Because velocity varies turbulent conditions are

expected.

Turbulence

• Thermal Turbulence• Presents the biggest problem for aviators during

landing.• To eliminate during normal flight, climb above

clouds.• Not confined to summer months.• When cumulus clouds are present, convection

currents and thermal turbulence exists.

Turbulence

• Mechanical Turbulence - Low Level• Results from strong wind gusts over rough

terrain or manmade features.• Produces turbulent eddies below 500 feet.

Turbulence

• Mechanical Turbulence - Wake Turbulence• Caused by aircraft flying through air.• Presents a major hazard to another aircraft

following too close.• Most hazardous during landings and takeoffs.

Turbulence

• Mechanical Turbulence - Mountain Wave

• Caused by wind speeds of 25 knots or stronger.• Produces a large-scale wave motion.• Extends from ground level to tropopause and

300 nmi downwind.• Most intense turbulence will occur within the

first two or three waves.

Turbulence - Wind Shear

Turbulence

• Wind Shear - Low Level Wind Shear (LLWS)• Occurs below 10,000 feet.• Primarily caused by frontal systems, low level jet

streams and thunderstorms.• Occurs rapidly.

Turbulence

• Wind shear - Clear Air Turbulence (CAT)• Occurs above 15,000 feet.• Not restricted to clear skies.• Turbulence occurs in vicinity of upper level

jetstream.

Normal Weather Patterns

Climatic Provinces

Normal Weather Patterns

• Superhumid Province• Lies along the north Pacific coast.• Precipitation from 30 to 150 inches per year.• Temperatures are mild and summers dry.• Cloudiest part of the country.

Normal Weather Patterns

• Humid Province• Area east of a line form Texas Gulf Coast to

Lake Superior.• 30 to 50 inches of rain annually.• Average temperature from 40o F in north, 70o F

along the Gulf of Mexico, 75o F in Florida. • Cold waves in winter, heat waves in summer.• Hurricanes are common.

Normal Weather Patterns

• Subhumid Province• Belt 300-500 miles wide just west of humid

province.• Average rainfall 18 to 30 inches.• Cold in winter, hot in summer.• Quick and severe temperature changes.• Tornadoes in most of southern part of this area.

Normal Weather Patterns

• Semiarid Province• 300-500 mile wide area west of subhumid

province from Canada to Mexico.• Precipitation ranges from 12 to 25 inches.• Warm, dry air masses common in winter.• Hail frequent in spring and early summer.• The Great Valley of California is

geographically separated from rest of province.

Normal Weather Patterns

• Arid Province• Includes parts of California, Texas, Arizona,

New Mexico, Nevada and Utah.• Less than 10 inches of rain annually.• Hot and dry summers, winters above freezing.• Clear dry air and plenty of sunshine.

Normal Weather Patterns

• Hawaii• Two major factors determine weather.

• Dramatic heights and contours of land areas.

• Prevailing northeast trade winds. • Pleasant temperatures.• Little distinctions between summer and winter.

Normal Weather Patterns

• Alaska• Has several different kinds of weather.• No great extremes in southern part of state.• Arctic slope lies in northern part of state.• Broad valley and low mountain ranges.

• Continental weather.

• Temperatures from -70o F in winter to 90o F in summer.

Summary

1. Clouds

2. Air Masses and Fronts

3. Terrain Factors

4. Turbulence

5. Normal Weather Patterns