Weather Patterns Air Masses and Fronts Section 17.1

Air Masses Arctic Maritime polar Continental polar OK Maritime tropical Continental tropical Huge bodies of air that have similar temperature, humidity, and air pressure

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 Fast moving cold dense air pushes slow moving warm air up Warm air cools and precipitates 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

Warm Front Less dense warm air moves over dense cold air Fast moving warm air overtakes slow moving cold air Less dense warm air moves over dense cold air Can produce rain or snow Area likely to become warm and humid

Warm Front

Stationary Fronts Standoff between two air masses 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 masses The denser air mass pushes the warm air mass up The two cold air masses may mix underneath the warm one The warm air mass is cut off (occluded) from the ground The 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