24.1 and 24.2 Notes

Air Masses & FrontsSection 24.1 & 24.2

What is weather?· state of the atmosphere at a given place and time· includes the amount and type of clouds, rain, snow, lightning, wind speed, pressure, and temperature

How Air Moves· air moves from high pressure to low pressure regions

high pressure = cold air sinks (poles)low pressure = warm air rises (equator)

· air moves from poles toward equatorinfluenced by the Coriolis effect

Air Masses· small pressure differences means air remains stationary or moves very slowly· air mass - large body of air with the same temperature and moisture content

polar (P) - coldtropical (T) - warmmaritime (m) - moist; form over oceancontinental (c) - dry; form over land

· combine polar/tropical with maritime/continentalex. continental polar (cP) - cold, dry airex. maritime tropical (mT) - warm, moist air

North American Air Masses· continental Tropical

deserts of southwest USdry, hot weather in summerdo NOT form in winter

· maritime TropicalAtlantic - mild, cloudy weather

in winter & hot, humid weather with thunderstorm in summer

Pacific - do NOT reach Pacific coast

· continental Polarcool, dry weather in summer & very cold weather in winter

· maritime PolarPacific - cool, foggy weather in summer & rain and snow

in winterAtlantic - cool weather, low clouds, and fog in summer &

cold, cloudy weather and snow in winter

Fronts· boundary that separates different air masses

brings a change in temperature and wind direction· cold fronts

cold air advances into a region occupied by warm air and lifts the warm air up

creates short-lived and violent stormscumulonimbus clouds form (thick, fluffy, and low in

sky)· warm fronts

cold air mass retreatswarm air rises over cooler aircirrus clouds form (long & wispy)rain over a large area, may cause violent weather

Click for animation

24.1 and 24.2 Notes

Severe Weather - Thunderstorms· severe weather = weather that causes property damage or loss of life· thunderstorms

caused by the upward movements of warm, moist,unstable air

associated with cumulonimbus clouds that generateheavy rainfall, lightning (released electricity fromclouds), and thunder (loud noise produced when electricity heats the air and causes it to expand rapidly)

Severe Weather - Hurricanes· greatest storms on Earth · wind speeds over 120 km/h (74 mph)· formed by the energy created as water condenses· measured by the Saffir-Simpson scale (1 = least damaging; 5 = most damaging· damages created by winds, flooding, storm surges (rising sea level and large waves)

Severe Weather - Tornadoes

Click for Texas Tornado video - April 2012

· smallest, most violent, and shortest-lived severe storm· occur when thunderstorms meet high-altitude, horizontal winds causing the air to rotate and form a funnel-shaped cloud· winds speeds can exceed 400 km/h (248.5 mph)· most occur in Tornado Alley (Texas to midwest) during late spring and early summer