Sep 2012Lesson 4.6

Meteorology

Air Masses & Fronts

Reference

From the Ground Up

Chapter 6.6 & 6.7:

Air Masses & Fronts

Pages 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 Front

Slope 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 – Meteorology

Precipitation, Fog & Thunderstorms

From the Ground Up

Chapter 6.8, 6.9:

Precipitation, Fog & Thunderstorms

Pages 147 - 154