Weather Patterns and Severe Storms PDF

Weather Patterns and Severe Storms Air Masses  Large bodies of air  1600 kilometers (1000 miles) or more across  Perhaps several kilometers thick  Similar temperature at any given altitude  Similar moisture at any given altitude  Move and affect a large p...

Weather Patterns and Severe Storms Air Masses  Large bodies of air  1600 kilometers (1000 miles) or more across  Perhaps several kilometers thick  Similar temperature at any given altitude  Similar moisture at any given altitude  Move and affect a large portion of a continent Invasion of Frigid Air Air Masses  Source region – the area where an air mass acquires its properties Air Masses  Classification of an air mass  By source region  By nature of surface in source region Air Masses  Polar (P)  High latitudes  Cold  Tropical (T)  Low latitudes  Warm Air Masses  Continental (c)  Form over land  Likely to be dry  Maritime (m)  Form over water  Humid air Air Masses  Four basic types of air masses  Continental polar (cP)  Continental tropical (cT)  Maritime polar (mP)  Maritime tropical (mT) Air-Mass Source Regions for North America Air Masses and Weather North America – cP and mT air masses – most important, especially east of the Rockies Air Masses and Weather  North America (east of Rocky Mountains)  Continental polar (cP)  Responsible for lake-effect snows  cP air mass crosses the Great Lakes  Air picks up moisture from the lakes  Snow occurs on the leeward shores of the lakes  From northern Canada and interior of Alaska  Winter – brings cold, dry air  Summer – brings cool relief Lake Effect Snow Air Masses and Weather  North America (east of the Rocky Mountains)  Maritime tropical (mT)  From the Gulf of Mexico and the Atlantic Ocean  Warm, moist, unstable air  Brings precipitation to the eastern United States Air Masses and Weather Continental tropical (cT) Southwest and Mexico Hot, dry Seldom important outside the source region Air Masses and Weather  Maritime polar (mP)  Brings precipitation to the western mountains  Occasional influence in the northeastern United States causes the “Nor’easter” in New England with its cold temperatures and snow Fronts  Boundaries that separate air masses of different densities  Air masses retain their identities  Warmer, less dense air forced aloft  Cooler, denser air acts as wedge Fronts  Warm front  Warm air replaces cooler air  Shown on a map by a red line with semicircles  Small slope (1:200)  Clouds become lower as the front nears  Slow rate of advance  Light-to-moderate precipitation Warm Front Fronts  Cold front  Cold air replaces warm air  Shown on a map by a line with triangles  Twice as steep (1:100) as warm fronts  Advances faster than a warm front Fronts  Cold front  Associated weather is more violent than a warm front  Intensity of precipitation is greater  Duration of precipitation is shorter  Weather behind the front is dominated by  Cold air mass  Subsiding air  Clearing conditions Cold Front Fronts  Stationary front  Flow of air on both sides of the front is almost parallel to the line of the front  Surface position of the front does not move Fronts  Occluded front  Active cold front overtakes a warm front  Cold air wedges the warm air upward  Weather is often complex  Precipitation is associated with warm air being forced aloft Formation of an Occluded Front Thunderstorms  Features  Cumulonimbus clouds  Heavy rainfall  Lightning  Occasionally feature hail Thunderstorms  Occurrence  2000 in progress at any one time  100,000 per year in the United States  Mostfrequent in Florida and eastern Gulf Coast region Average Number of Days per Year with Thunderstorms Thunderstorms  All thunderstorms require Warm air Moist air Instability (lifting) High surface temperatures Most common in the afternoon and early evening Thunderstorms  Require continuous supply of warm air and moisture  Each surge causes air to rise higher  Updrafts and downdrafts form  Eventually precipitation forms  Most active stage  Gusty winds, lightning, hail  Heavy precipitation  Cooling effect of precipitation marks the end of thunderstorm activity Thunderstorm Development Doppler Radar Hurricanes  Wind speed in excess of 119 kilometers (74 miles) per hour  Rotary cyclonic circulation  Form between the latitudes of 5 degrees and 20 degrees Regions Where Hurricanes Form Hurricanes  Known as  Typhoons in the western Pacific  Cyclones in the Indian Ocean  North Pacific has the greatest number per year Hurricanes  Parts of a hurricane  Eye wall  Near the center  Rising air  Intense convective activity  Wall of cumulonimbus clouds  Greatest wind speeds  Heaviest rainfall Hurricanes  Parts of a hurricane  Eye  At the very center  About 20 kilometers (12.5 miles) diameter  Precipitation ceases  Winds subsides  Air gradually descends and heats by compression  Warmest part of the storm Super Typhoon Jangmi Cross Section of a Hurricane Hurricanes  Wind speeds reach 300 km/hr  Generate 50 foot waves at sea Hurricanes  Hurricane formation and decay  Form in all tropical waters except the  South Atlantic and  Eastern South Pacific  Energy comes from condensing water vapor  Developmost often in late summer when warm water temperatures provide energy and moisture Sea Surface Temperatures Hurricanes  Initial stage is not well understood  Tropicaldepression – winds do not exceed 61 kilometers (38 miles) per hour  Tropicalstorm – winds between 61 to 119 kilometers (38 and 74 miles) per hour  Name is given at this stage Hurricanes  Hurricane formation and decay  Diminish in intensity whenever  They move over cooler ocean water  They move onto land  The large-scale flow aloft is unfavorable Hurricane Fran Hurricanes  Destruction from a hurricane  Factors that affect amount of hurricane damage  Strength of storm (the most important factor)  Size and population density of the area affected  Shape of the ocean bottom near the shore  Saffir-Simpson scale ranks the relative intensities of hurricanes Hurricanes  Categories of hurricane damage  Storm surge – large dome of water 65 to 80 kilometers (40 to 50 miles) wide sweeps across the coast where eye makes landfall  Wind damage  Inland flooding from torrential rains Storm Surge Destruction