Chapter 20Weather

20.1Air Masses and Weather20.2Fronts and Lows20.3Thunderstorms and Tornadoes20.4Hurricanes and Winter Storms20.5Forecasting Weather

20.1Air Masses and Weather

Objectives1) What are the factors that determine the characteristics

of an air mass?2) How are types of air masses the same? Different?

Introduction Meteorology: the study

of processes that govern Earth’s atmosphere, helps make weather predictions possible

Meteorologist: a scientist that studies meteorology Ranges from making

weather forecasts to studying how tornadoes develop

http://science.howstuffworks.com/nature/28810-science-of-storm-chasing-meteorology-science-video.htm

Origin of an Air Mass

Air mass: a large body of air in the lower troposphere that has similar characteristics throughout Temperature and

humidity are nearly uniform

Origin of an Air Mass Cont’d

Temperature and humidity depend on where the air mass comes from North = cold South = warm

Origin of an Air Mass Cont’d

Moisture content of an air mass also depends on the underlying surface Stays over land for a

long time = dry Stays over water +

absorbs water vapor = humid

Origin of an Air Mass Cont’d

Air masses take the temperature and humidity of its place of origin

Characteristics may change as it travels Affects the weather of the area it enters and gradually heats up as

it moves over a warmer surface (cools down over a colder surface)

Types of Air Masses

Air masses are classified by where they originate Temperature: arctic,

polar, or tropical region

Humidity: land (continental) or sea (maritime)

Continental Arctic (cA)

Originate in the arctic regions

Capable of causing extreme cold waves in the regions they enter

Very dry

Continental Polar (cP) Originates over the inland regions of Alaska and Canada Somewhat warmer than cA Usually cold and dry Sometimes can create precipitation

Lake-effect snow: air passes over the Great Lakes in the late fall when the water is still warm, the cold, dry air picks up moisture from the lakes, then deposits the heavy snow

Maritime Polar (mP)

Originate over the ocean in high latitudes

Cold and damp Not usually as cold as cP

b/c oceans are warmer than land

Cools to dew point Fog, clouds, or

precipitation

Maritime Tropical (mT)

Originates over a warm tropical ocean Warm and humid Air from the Bahamas and the Gulf of Mexico moves

clockwise around the high pressure over the Atlantic Ocean Brings heat and humidity to Midwestern and Eastern US Thunderstorms develop during the heat of the day

Humid air is heated from below and rises

Continental Tropical (cT) Originates over deserts Hot and dry Often begins as a

maritime air mass but becomes dry as it passes over mountains

Makes tremendous heat waves during summer

Doesn’t bring clouds or thunderstorms

A drought occurs if cT air advances into an agricultural region

20.1 Exit Ticket