Fronts & Air MassesTwin Spruce 7th Grade Science

Weather Identifiers

• Temperature

• Pressure

• Wind Speed & Direction

• Observable Conditions

Air Pressure• Low Pressure:

‣ spins counter-clockwise…“low & loose”

‣ brings storms

• High Pressure:

‣ spins clockwise…“high & tight”

‣ brings clear skies

• Isobars: shown on weather maps as lines of equal pressure (998 mb line, 996 mb line, 994 mb line, etc.)

H

L

Air Mass Properties• Temperature

‣ Hot or Cold

• Moisture Content

‣ Wet or Dry The type

of air mass is always defined

based on where it FORMED!

Air Mass Types• Polar air (P)

‣ 60°N & northward to pole

‣ Cold air

• Tropical air (T)

‣ 25°N & southward to equator

‣ Hot air

The type

of air mass is always defined

based on where it FORMED!

Air Mass Types• Maritime air (m)

‣ Located over the ocean

‣ Wet air

‣ Maritime comes from the word “marine”

• Continental air (c)

‣ Located over land

‣ Dry air

The type

of air mass is always defined

based on where it FORMED!

Air Mass Types• m + P = Maritime Polar (mP)

‣ Wet & Cold

• m + T = Maritime Tropical (mT)

‣ Wet & Hot

• c + P = Continental Polar (cP)

‣ Dry & Cold

• c + T = Continental Tropical (cT)

‣ Dry & Hot

The type

of air mass is always defined

based on where it FORMED!

Courtesy of Stormstalker

Fronts• Boundary zone where two different “air masses” meet

• Noticeable change in air mass properties (pressure, temperature, wind, etc.)

• A front’s width can range from a few miles to several dozen miles

Cold Front• Temperature falls after front passes

• Pressure falls ahead of front

• Noticeable wind direction shift

• Most likely front to include severe storms (rain, hail, tornado, lightning, etc.) ahead of or along the front

Cold Front

Warm Front

• Temperature rises after front passes

• Slight wind direction shift

• Light to moderate precipitation ahead of front

Warm Front

Stationary Front• No motion or very little motion for a few days

• Noticeable differences from one side of front to the other (temperature, wind, etc.)

• Cloudy along and either side of front

• Usually an extended period of precipitation along and either side of front

Stationary Front

Occluded Front• Pressure falls ahead of either front

• Temperature…

‣ Falls behind front (cold-type occlusion)

‣ Rises behind front (warm-type occlusion)

• Moderate to heavy precipitation ahead of & behind front

Occluded Front