Download Chapter 25 Notes Air Masses Fronts - West Windsor

Chapter 25 Notes Air Masses •
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Differences in air pressure at different locations create wind patterns. Air moves from areas of high pressure to areas of low pressure. Coriolis effect – causes the deflection of winds due to Earth’s rotation (to the right in the Northern Hemisphere) Air mass – a large body of air with uniform temperature and moisture content o Take on the characteristics of the region in which they form: ƒ Maritime (m) – form over oceans, moist ƒ Continental (c) – form over land, dry ƒ Polar (P) – form over polar areas, cold ƒ Tropical (T) – form over tropical areas, warm o The above combine to form the 4 main types of air masses: mP, mT, cP, cT Fronts •
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Front – boundary between air masses of different density and temperature Cold front – when cold air moves into an area cold air o Moving cold air lifts warm air o Temperature goes from warm to cold warm air o Produces cumulus and cumulonimbus clouds o Precipitation is quick and violent including T‐storms and hail o May form squall line – long line of heavy thunderstorms Warm front – when warm air moves into an area o Less dense warm air rises over cooler air with gradual slope cold air o Temperature goes from cold to warm o Produces cirrus, stratus, and nimbostratus clouds warm air o Lighter precipitation covers a large area and lasts longer o Steady rain or snow is produced Stationary Front – two air masses meet by neither is displaced cold air o Two air masses may move parallel to front line o Weather is similar to a warm front warm air Occluded Front o Boundary formed where a fast‐moving cold air mass overtakes and lifts a warm air mass completely off the ground o Weather is similar to a cold front o Complicated weather can be hard to predict Wind patterns may also change with a passage of a front cold air
moving down warm air
moving up Weatheer Maps •
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Issobars – line
es of equal pressure o Closerr lines = greaater pressure differencee = greater w
wind in that aarea o Widelly spaced lines = slow ch
hange in presssure = low wind speedss o Isobarrs from circlees – indicatees centers off high and lo
ow air pressu
ure o Usually drawn eveery 4 millibaars H
High pressure
e – relative p
pressure maaximum with
h diverging w
winds – FAIR
R weather •
H Windss blow from h
high pressu
ure to low preessure. Becau
use of the Corriolis Effectt, winds curvee to the right in the Northeern Hemissphere. H Win
nds go outwarrd and clockwise fro
om an aarea of high presssure formingg an “antticyclone” in the Norrthern Hemisp
phere Lo
ow pressure
e – relative p
pressure min
nimum with converging winds – STO
ORMY weath
her L Windss blow from h
high pressu
ure to low preessure. Becau
use of the Corriolis Effectt, winds curvee to the right in the Northeern Hemissphere. L Win
nds go inward
d and counter‐clockwisse wards an area of tow
high
h pressure forrming a “ccyclone” in the Norrthern Hemisp
phere •
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Issotherms – lines of equaal temperatu
ure o Usually drawn eveery 10°F on a weather m
map Sttation mode
el – cluster o
of weather symbols plotted on a maap indicatingg the weatheer co
onditions at a particularr observation
n station Temperature, wind direction, wind speed, cloud cover, and p
precipitation
n can usuallyy be orecasted acccurately, bu
ut it is often difficult to p
predict preciisely when p
precipitation will fo
occur or the e
exact amoun
nt that will fall. W
Weather in th
he continenttal US often moves from
m west to easst because o
of the W
Westerlies.