WeatherPart 5: Weather Patterns

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Air Masses• Large bodies of air• Movement of them

causes changes in weather• Cover thousands of

square kilometers• Properties fairly

uniform• Classified by where

they form

• Continental – form over continents; relatively dry• Maritime – form over

oceans; relatively humid• Polar – cold• Tropical - warm

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4 Major Air Mass Types in USA1. Maritime tropical – • Forms over ocean near

the equator• Warm, moist air• Most commonly affects

Eastern states• In summer brings hot,

humid weather• In winter brings rain or

snow if it encounters a cold air mass 3

4 Major Air Mass Types in USA

2. Maritime polar –• Forms over northern

Atlantic and northern Pacific oceans• Cool, moist air• Bring cloudy, damp

weather to Northeast and Pacific Northwest

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4 Major Air Mass Types in USA

3. Continental tropical – • Hot and very dry• Forms over the desert

southwest and Mexico usually during summer• Affects southwest

states, plains, and Mississippi valley and can bring record high temperatures 5

4 Major Air Mass Types in USA

4. Continental polar – • Cold and dry• Forms over Canada • Often dominant

weather in winter• Brings very cold

weather• Can also bring clear,

pleasant weather to the North in summer 6

Major Air Mass Types

• mT = Maritime Tropical• mP = Maritime

Polar• cT = Continental

Tropical• cP = Continental

Polar

7cA = Continental Arctic (5th type)Brings extremely cold temperatures with very little moisture, originate north of the arctic circle in winter

Fronts• A front is a boundary

that forms when two air masses with different properties meet• Weather is usually

unsettled and stormy along a front.

4 types of fronts:• Cold• Warm• Occluded• Stationary

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Cold Front• Cold air mass meets

and pushes under a warm air mass • Pushes warm air up• Can cause violent

storms• Fair, cool weather

usually follows a cold front

• Generally move northwest to southeast• Can cause a rapid

drop in temperature of more than 15° in one hour

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Cold Front• Weather symbol:

blue triangles point in the direction the cold front is moving

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http://commons.wikimedia.org/wiki/File:Example_of_a_cold_front.svg

Warm Front

• Warm air overtakes cold air and goes over it• Showers followed by hot, humid

weather• Noticeably warmer after the front passes• Generally move southwest to northeast

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Warm Front• Weather symbol: Red,

semicircles pointing in the direction the warm front is moving

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http://commons.wikimedia.org/wiki/File:Example_of_a_warm_front.svg

Occluded Front• A cold front moves

faster than a warm front• When a cold front

overtakes a warm front an occluded front forms• Usually form around

low pressure areas

• At the occluded front the cold air mass meets the cool air mass that was ahead of the warm front• Warm air rises to

form cumulonimbus or nimbostratus clouds bringing precipitation 13

Occluded Front• Weather symbol:

purple, alternating triangles and semicircles pointing in the direction the front is moving

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https://commons.wikimedia.org/wiki/File:Occluded_cyclone.svg

http://commons.wikimedia.org/wiki/File:Occlusiefront.png

Stationary Front• When warm air

meets cold air and no movement occurs• Rain may fall for

many days

• Weather Symbol: Alternating blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air

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