WEATHER LECTURE NOTES

VOCABULARY: air mass; source region; continental polar; maritime polar; continental tropical; maritime tropical; equatorial; arctic; polar front; front; warm front; cold front; occluded front; stationary front; cyclone; anticyclone; middle latitude cyclone; tropical cyclone; hurricane; typhoon; eye; tornado; thunderstorm; cumulus stage; mature stage; dissipating or anvil stage


air mass--huge section of troposphere, temperature and humidity are fairly uniform at any given level

contact with the surface gives an air mass its uniform temperature and humidity

source regions:

moisture

maritime or continental (m, c)

temperature

equatorial (E)

tropical (T)

polar (P)

arctic (A) or antarctic (AA)

makes:

mE, mT, mP, mA, cE, cT, cP, cA, but cE and mA do not occur

source region identification

typical weather of an air mass:

warm air mass--cool near bottom because of cold land, possible condensation, fog

cold air mass--warmed near bottom, convection, cumulus clouds, good visibility, windiness; how much moisture is important, often fair unless warmed below

AIR MASSES MOVE

front--boundary between two different air masses

warm air is less dense so rises over colder denser air

rises, cools, and may condense

earth's rotation makes frontal surface a gentle slope

4 types of fronts

map symbols--show frontal boundary location at the earth's surface

cold front--cold air moves in to replace warm air, steep blunt nose, warm air rises quickly, short period of heavy precipitation

Complete the cold front weather on the cross-section

warm front--warm air moves in to replace cold air, gentle slope ahead of the surface location of the front, warm air rises slowly above, condensing in advance of the front, wide area of slow, steady precipitation

Complete the warm front weather on the cross-section

stationary front--conditions similar to a warm front, however, the front is remaining in relatively the same position

Complete the stationary front weather on the cross-section

Complete the middle-latitude cyclone development map

Complete the pre-occlusion cross-section

occluded front--mature stage of a middle-latitude cyclone, the cold front overtakes the warm front and lifts the warm air off of the ground, the warm air rises, cools, condenses

Complete the occluded front cross-section

development of a middle-latitude cyclone

polar front--separates the prevailing westerlies from polar easterlies, wave motion develops, moves east

between them are tongues of cold polar air moving toward equator which are ANTICYCLONEs--high, clear, cloudless weather, CLOCKWISE winds

cold fronts move faster than warm fronts

occlusion--cold front type, coldest follows

winter middle latitude cyclones are better developed, move faster, and are more frequent

middle latitude cyclones are the main source of precipitation in the middle latitudes--moving rising air, cyclone, LOW--COUNTER-CLOCKWISE winds

summary:

2 air masses so change in weather

temperature varies

wind direction and velocity changes

dew point changes

barometer falls as front approaches, rises as passes

note weather maps

hurricanes--tropical cyclones, typhoons

differ from middle latitude cyclones:

more intense

200-400 miles diameter

very steep pressure gradient

very low pressure center

no fronts

move slowly through the tropics, speed up in middle latitudes

all originate on west side of oceans in doldrums

latent heat of condensation feeds them

tracks

storm surge accounts for majority of the fatalities

tornadoes

latent heat of condensation feeds, low pressure

watch--the necessary conditions exist

warning--it's too late somewhere

thunderstorms--3 stages

cumulus stage--strong updrafts of warm air, grows above freezing level, ice crystal and snow and raindrops, 10-15 minutes after top freezes

mature stage--precipitation to surface, draws air down, downdrafts in lower forward half, updrafts in rear, reach 40,000', hail, strong drafts, surface gust of wind, heavy rain, downdraft over lower half, 15-20 minutes total

dissipation or anvil stage--down drafts spread entire cell, condensation stops, rain ends, strong winds in highest level tilt top, dissipates


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