Sep 2012Lesson 4.6

Meteorology

Air Masses & Fronts

Reference

From the Ground UpChapter 6.6 & 6.7:Air Masses & FrontsPages 140 - 147

Introduction• Giant air masses move around with the

winds and rotate around pressure systems to bring different weather to areas.

• It’s important to know what types of air masses and fronts exist, how they form, and what kind of weather they will cause

Outline• Air Masses• Fronts

Air Masses• Large section of troposphere with

uniform properties of temperature and moisture in the horizontal

• May be several thousand miles across

• Takes on properties of surface over which it forms (known as Modification)

Classifications• Classifications

– Continental Dry c– Maritime Moist m

– Arctic Cold A– Polar Moderate P– Tropic Warm T

• Main types in North America in winter = cA, mA, mP

• Main types in North America in summer = mA, mP, mT

Air Masses

Cold Air Mass Warm Air Mass

Stability Unstable Air Stable Air

Turbulence Turbulent Smooth

Visibility Good Poor

Clouds Cumulus Stratus, Fog

Precipitation Showers, Hail, Thunderstorms

Drizzle

Fronts• Transition zone between two air masses

Cold Front Warm FrontSlope Steep 1:50 Shallow 1:200

Weather Severe (unstable) Mild (stable)

Clouds Cumulus Stratus

Winds Veer Veer

Precipitation Showers Steady, Storms

Temperature Cools Warms

Fronts• Cold Front

– Leading edge of advancing cold air mass– Faster the front, the more severe the thunderstorm

Fronts• Warm Front

– Trailing edge of retreating cold air mass– Indicated by high to low stratus clouds

Other Fronts• Stationary Front

– Cold air neither advancing nor retreating

• Occluded Front (AKA Occlusion)– Cold front overtakes warm front, lifts warm air up

• Trowal (Trough of Warm Air Aloft)– Warm air lifted by occluded front

Next Lesson

4.7 – MeteorologyPrecipitation, Fog & Thunderstorms

From the Ground UpChapter 6.8, 6.9:Precipitation, Fog & ThunderstormsPages 147 - 154