Download - What Causes Our Daily Weather To Change?
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What Causes Our Daily Weather To Change?
Change in our weather
is a result of a change in air
masses.
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What Is An Air Mass? An air mass is a large body of air in
the lower troposphere that has similar characteristics throughout.
An air mass can be several thousand kilometers in diameter and several kilometers high
The temperature and humidity are nearly uniform throughout
The temperature and humidity depend on where the air mass originates.
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Where Do Air Masses Originate?
Air masses originate in source regions.
Source regions have flat, uniform composition and light winds.
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How Are Air Masses Classified?
The temperature of each air mass depends on whether the air mass originates in an arctic, polar, or tropical source region.
The humidity depends on whether the air mass originates over land ( continental ) or over water ( maritime ).
Air masses are classified by temperature and humidity.
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Air Mass ClassificationAir Mass Symbol Temperature &
HumidityWhere Air
Mass Forms
Area of the Country that is Impacted
Southwest and
Southeast U.S.
Northeast and Northwest
U.S.Midwest to
Eastern U.S.
Southwest U.S.
Northern U.S. in winter
Maritime Tropical
Continental Tropical
Maritime Polar
ContinentalPolar
ContinentalArctic
mT
mP
cA
cT
cP
Warm and Wet
Very Cold and Dry
Cold and Wet
Warm and Dry
Cold and Dry
Low latitudesover water
High latitudesover water
High latitudesover land
Low latitudesover land
High latitudesover land
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mP – West Coast• Tends to be
unstable • Heavy rains as
cool moist air flows over mountains along west coast • mP is modified by
time it reaches interior of US, though is milder that cP• (how???)
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mP – East Coast• Not as common
as west coast mP • Colder than west
coast mP• Usually brought
onshore by high pressure to the north of us and/or low pressure to the south moving up the coast.
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Maritime Tropical Air Mass
West Coast East Coast• Brings showers and thunderstorms • Summer - Brings showers and
thunderstorms• Winter – snow or heavy rain
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Continental Tropical Air Mass – Summer only
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Continental Polar Air Mass
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Types of Air Masses
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Global Source Regions For Air Masses
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Stability of an Airmass Changes to the stability of an air mass can
result from temperature differences between an air mass and the surface
The stability of an air mass may be shown using a third letter:
"k“ = un-stable or "w“ = stable
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Air Mass Source Region – Practice Quiz
Continental Arctic
ContinentalPolarMaritime
Polar
MaritimePolar
ContinentalTropical
MaritimePolar
MaritimeTropical
MaritimeTropical
1.
2.3.
4.
6. 8.
7.
5.
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Weather Patterns• Weather patterns are caused by the
movement of air masses and what happens when different air masses collide.• Front – boundary between two air masses.• Air masses meet but do not mix.
The boundary line between the offensive and
defensive lines would be a front.
Front
Great Air
Mass
Poor AirMass
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Name Formation Clouds Weather Symbol
•Wind, heavy rain•Thunderstorms•Lightning•Colder air after front passes
•Clouds then gentle, steady rain arriving before the front•Steady rain for days along front if stationary too long•Strong winds and heavy rains
Cold•Altocumulus•Cumulonimbus
Warm
Stationary
Occluded
Air masses stop moving
•Cirrus•Cirrostratus•Altostratus•Nimbostratus•Cirrus•Cirrostratus•Altostratus•Nimbostratus
•Cumulus•Cumulonimbus
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Fronts Cold Front: boundary between
advancing cold air mass & a warmer air mass it is displacing Rising warm air usually produces
precipitation if wet Air becomes colder after front passes
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Fronts Warm Front: boundary between
advancing hot air mass & a colder air mass it is displacing 1st clouds days in advance, then RAIN Air becomes warmer after front passes
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Fronts Occluded Front: when cold front ‘catches
up’ to a warm front, producing clouds & precipitation
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Fronts Stationary front: when a front stops
moving forward, producing clouds & precipitation – causes floods if stationary too long
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The Life Cycle Of A Cyclone (Low Pressure System)• The United States often experiences weather due to
the boundary between the cold air masses of the Polar Easterlies and the warm air masses of the Prevailing Westerlies. This arrangement results in a weather conditions called a Traveling Cyclone.• The formation of a cyclone
is called "cyclogenesis". Cyclones form in areas of low pressure.
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The Life Cycle Of A Cyclone (Low Pressure System)•The process begins when two air masses of different densities and temperatures move in opposite directions along a polar front resulting in a large temperature gradient.
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The Life Cycle Of A Cyclone (Low Pressure System)•Cyclones are the result of instability forming along the polar front, resulting in a wave developing between the cold and warm air masses. The fronts are separated, and the warm front begins to move north as the cold front begins to move south
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The Life Cycle Of A Cyclone(Low Pressure System)
•The pressure at the center of the cyclone continues to get lower as the cyclone continues to form. Clouds ahead of the warm front begin to precipitate over a large area of surface, and clouds along the cold front begin to precipitate over a narrow stretch [along the cold front]. As the pressure is lowered, wind speeds increase.
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The Life Cycle Of A Cyclone ( Low Pressure System)
•The cold front continues to move eastward, speeding to overtake and undercut the warm front. This is called occlusion. It is at this point which the cyclone is at its peak. The area of the warm sector is decreasing.
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The Life Cycle Of A Cyclone (Low Pressure System)
•By the time the cold front completes occlusion with the warm front, the air in the warm sector is lifted upward as the cold air replaces it at the surface. The system is stabilizing.
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Weather Forecasting
Satellites
Radiosondes
Surface observations
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Station Model
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Surface Weather Map
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Locating a Front Wind direction changes Temperature changes sharply Dew Point changes sharply
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Forecasting Computer models take current data & plug it
into equations to predict weather
Meteorologists take computer models & tweak them to fit their experience with local conditions
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ForecastingTrend Method: using past movement of a front &
precipitation to predict future movement
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Practice reading a weather map
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