Weather Lesson Seven Air Masses and Fronts

AIR MASSES Large bodies of air in the troposphere with similar temperature, moisture and pressure characteristics. Forms over large areas called source regions. Air mass stays over an area for a while to pick up characteristics of that region.

AIR MASS SOURCE REGIONS 1. POLAR (P) - cool air from the north (Canada or Arctic). 2. TROPICAL (T) - warm air from the south. 3. CONTINENTAL (c) - air mass formed over land - DRY. 4. MARITIME (m) - air mass formed over water - MOIST.

m c P T cT - dry and warm cP - dry and cold mT - moist and warm mP - moist and cold

cA mP mP cP cT mT mT

FRONTS The boundary between two air mass. Little mixing of air occurs at fronts. Unstableness of fronts is the cause of precipitation. 4 types of fronts and they are . . .

COLD FRONT The boundary between an advancing air mass pushing a warmer air mass. Underlying cold air pushes warm up and over like a plow. A fast moving front. Symbol used on maps is

WARM FRONT The boundary between an advancing warm air mass on a retreating wedge of a cold air mass. Warm air rises up and over as its advances because it is less dense. A slow moving front. Symbol used on maps is

OCCLUDED FRONT Occurs when a cold front overtakes a warm front and pushes the warm air between them up off the ground. Symbol used on maps is

STATIONARY FRONT Boundary between two adjacent air masses of different characteristics remaining in approximately the same position. Symbol used on maps is

Symbols point in the direction the air mass is moving.

WAVE CYCLONE The typical pattern of storms (or low pressure systems) as they travel across the United States. Storms have a low pressure center with a wedge of a cold front and a warm front extending from the center.

L

STORM TRACKS Low pressure storms generally track (move) to the east (or northeast) across the United States. Due to the wind belt in which the United States is located.

WEATHER PREDICTION Weather prediction is based on probability. A few days predictions are more accurate and reliable than long term predictions. Computer analysis and satellite images have improved forecasting in recent years.