MET1010 CHAPTER 8

Air Masses

Large Bodies of air with homogenous characteristics

What are air masses classified based on ?

Temperature and Moisture

Source Region

where air mass originates

For any location to be a good source region what two things must be true

-Physically uniform: Either all land or all water

-Stagnating Circulation

What are the water vapor characteristics ?

c-continental: land/dry

m-maritimes: water/ humid

Temperature Characteristics

A-Artic (coldest)

P-Polar

T-Tropical

-E-Equatorial (hottest)

What are all the air mass clasifications?

cA, cP, cT, mP, mT, mE

cA

-Region: Artic Basin

- Dry and bitterly cold

-Stable

-North

-Associated Weather: Cold Waves

cP

- Canada/Alaska

-Dry and very cold; cold in winter and summer

-Stable

-South

-lake effect snow in the inter and cool waves in the summer

mP (Northeast Pacific)

-Characteristics: Moist and cool

-Unstable in the winter and stable in the summer

-South East

-Associated weather: heavy precip in the winter and light rain in the summer

mP (NorthWestern Atlantic)

-Characteristics: Most and cool

-Unstable in the winter and stable in the summer

-South West

-Associated weather: in the winter northeastern blizzards and in summer light rain and fog

cT

-SUMMER ONLY AIR MASS
-Southwestern US

-Dry and hot

-Unstable

-No motion

-Associated Weather:Drought like conditions

mT(Gulf or Carribean)

-Characteristics :Moist and warm

-Unstable

-North/ Northwest

-Associated weather: convective thunderstorms in the summer and advection fog in winter

mT (Subtropical pacific)

-30 degree latitude

-Characteristics: Moist and cool

-stable

-Northeast

-Associated weather: uplsope fog and maybe drizzleF

Fronts

-Boundaries between air masses and different densities

-Always force warm air to rise ( Low pressure)

Cold front

-Cold air is moving into a region occupied by warmer air

-Underrunning

-Fast moving front (30-35mph)

-Steep slope: enhances severe weather

-Dewpoint decreasing

-Temperature decreasing

-Wind Shift: South west to north west

Warm Front

-Warm air is moving into a region occupied by colder air

-Overrunning

-Slow-moving front (20-25mph)

-Gradual slope- decreases risk for severe weather

-Widespread clouds and rain

-Temperature increase

-Dew point increase

-Wind Shift: Southeast to southerly

Stationary front

-Does not advance because winds are parallel to the font

-Scattered clouds: showers in the late afternoon

-Small difference across the front

-Weakest of the four fronts

Occluded front

-Cold front overtakes a warm front

Midlatitude cyclone

Area of low pressure with fronts attached; primary weather producer in the middle latitudes (US)

Cyclogenesis

development of mid-latitude cyclone

-When occlusion first occurs, the cyclone is the strongest (mature)Cy

Cyclolysis

Weakening of mid-latitude cycloneW

What happens ahead of the warm front in a midlatitude cyclone?

The pressure falls slowly, the temperature is steady then rises slowly, the winds are east-southeast, and it can cause rain or snow that is changing to rain.

-Clouds: cirrus, cirrostratus, nimbostratus, altostratus, stratus

What happens behind a warm front in a midlatitude cyclone?

• The pressure rises slowly

• Temperature rises

• winds are southerly

• Warm sunny day

  • NO CLOUDS

What happens ahead of the cold front in a midlatitude cyclone?

-Pressure falls rapidly

-Temperature is steady but falls due to clouds moving in

-Wind is a gusty southwesterly

-Causes rain or thunderstorms

-Clouds: Cumulonimbus, stratus, nimbostratus

What happens behind a cold front in a midlatitude cyclone?

-The pressure rises rapidly

-The temperature falls

-The wind is a gusty north-westerly

-Cold, sunny day

-NO CLOUDS