Transcript Weather Elements

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
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Clouds
Air Masses and Fronts
Terrain Factors
Turbulence
Normal Weather Patterns
Types of Clouds
Low Clouds
• Stratus
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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.
Fog Types
• 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
• 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.
Fog Types
• 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.
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 lowpressure 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 lightcolored 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
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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
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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.
2.
3.
4.
5.
Clouds
Air Masses and Fronts
Terrain Factors
Turbulence
Normal Weather Patterns