Weather PatternsAir Masses and Fronts

Section 17.1

Air Masses

Huge bodies of air that have similar temperature, humidity, and air pressure

Maritime polar

Maritime tropical

Continental tropical

Continental polar

Arctic

OK

Fronts

• When an air mass moves into an area and interacts with other masses, it causes the weather to change.

• The boundary where air masses meet becomes a front

Cold Front

Since cold air masses move fast they can cause abrupt weather changes (thunder storms)

After a cold front passes, colder, drier air moves in bringing clear skies

Fast moving cold dense air pushes slow moving warm air up

Warm air cools and precipitates

Warm Front

Less dense warm air moves over dense cold airCan produce rain or snowArea likely to become warm and humid

Fast moving warm air overtakes slow moving cold air

Warm Front

Stationary Fronts

Cold air and warm air meet but neither can move the other.

Produces rain, snow or fog

Can last for several days

Standoff between two air masses

Stationary Fronts

Standoff between two air masses

Occluded Front

A warm air mass is caught between two cold air massesThe denser air mass pushes the warm air mass upThe two cold air masses may mix underneath the warm oneThe warm air mass is cut off (occluded) from the groundThe warm air cools, condenses and may precipitate

Cyclones & Anticyclones

• Fronts become distorted because of things like mountains or jet streams (bending)

• Bending can cause swirls which can create low pressure centers

Cyclones

• Swirling low pressure system

• Air pressure decreases as warm air rises

• Cooler air blows inward toward the low pressure area

• Coriolis effect causes the wind to spin counterclockwise in northern hemisphere

• Associated with clouds, wind, and precipitation

Anticyclones

• High pressure systems

• Air swirls outward in clockwise direction in northern hemisphere

• Cool air moves downward and heats up lowering relative humidity

• Associated with dry, clear weather