Weather Patterns Air MassesAir Masses FrontsFronts Cyclones/AnticyclonesCyclones/Anticyclones

Air Masses  Huge body of air w/similar: –Temperature –Humidity –pressure

Classifying Air Masses  Temperature –warm: tropical- form in tropics; low pressure –cold: polar- form in polar regions; high pressure  Humidity –humid: maritime- form over oceans –dry: continental- form over land in middle of continents

Four Major Air Masses  Maritime Tropical –Warm, humid air masses –Form over Gulf of Mexico & Atlantic Ocean- influence southeastern U.S. –West- form over Pacific Ocean  Maritime Polar –Cool, humid air masses –North Pacific & Atlantic Oceans –Affect west coast more than east coast; Why?!

Four Major Air Masses  Continental Tropical –Hot, dry air masses –Form only in summer over Southwest & N. Mexico –Cover smallest area in U.S.  Continental Polar –Cool, dry air masses –Form over central & northern Canada & Alaska

Fronts  As air masses move, they bump into each other & do not mix easily.  Front- area where 2 air masses meet  Often cause storms & changeable weather  Type of front depends on characteristics of air masses & their movement

Cold Fronts  Rapidly moving cold air mass runs into slower moving warm air mass  Cold air slides under less dense warm air pushing warm air up  Move quickly causing abrupt weather changes  Clouds- cumulonimbus clouds, followed by altocumulus & clearing  After front- cool & dry

Cold Front BeforeDuringAfter WindsS-SWGusty/shiftingW-NW TemperatureWarm Sudden drop Steadily dropping Pressure Falling steadily Minimum, then sharp rise Rising steadily Clouds Ci, Cs, Cn CnCu Precipitation Short showers Heavy rains, possible, thstorms Showers; clearing

Warm Front  Moving warm air mass collides with slowly moving cold air mass  Warm air moves over cold air  Humid warm air produces showers & light rain along front or scattered clouds if dry  May be foggy or rainy for several days  Clouds- cirrus, becoming cirrostratus; altostratus thickening & lowering becoming nimbostratus  After front- warm & humid

Warm Front BeforeWhileAfter WindsS-SEVariableS-SW Temperature Cool-cold; warming Steady rise Warmer, then steady PressureFalling Leveling off slight rise, then fall Clouds CiCi, Cs, As, Ns, St, fog; occas.Cb in summer Cs NsCb CiCs NsCbstratus-type clearing w/ scattered Sc; occas.Cb in summer ScCbScCb Precipitation Lt.-mod. rain, snow, sleet, or drizzle Drizzle or none Usu. None, possl. lt. rain showers

Stationary Fronts  Cold & warm air mass meet, but neither has force to move the other  May produce rain, snow, fog, or clouds  May bring clouds & precipitation for many days

Occluded Fronts  Most complex weather situation  Warm air mass caught between 2 cooler air masses  Temperature near ground becomes cooler  Warm air mass cut off or occluded  May be cloudy, rainy, or snowy  Clouds- warm sector: cumulus, stratocumulus

Cyclones  Swirling center of low air pressure  Counterclockwise spin of winds towards low pressure  Associated w/storms & precipitation

Anticyclones  High pressure centers of dry air  Winds spiral outward from high pressure spinning clockwise  Dry, clear weather

Quiz 