Post on 05-Jan-2016
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