GEOL 106 Lecture Notes - Lecture 33: Freezing Rain, Snow Drifts, Wind Chill
26 May 2018
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o storms in Colorado and along coast that produce heavy snowfall are derived from moist air
originating over Atlantic Ocean
o fast moving storms forming east of Canadian Rocking, called Alberta Clippers, are generally
drier with less snow and extreme cold temperatures
- blizzards can produce lengthy periods of heavy snowfall, wind damage, large snowdrifts
o e.g. Blizzard of 1888: killed more than 400 people and paralyzed northeastern US for 3 days
with snow drifts high as second floor buildings
- nor’esters: storms that move along east coast of US and Canada
o can produce blizzards
o wreak havoc with hurricane force winds, heavy snows, intense precipitation, high waves that
damage coastal areas
o most common between September and April and often create blizzard conditions in large
cities like New York
o Marh 1993: seere nor’easter paralyzed East oast → snow, tornadoes, flooding from
Alabama to Maine
- blizzards are generally more dangerous than other snow storms:
o wind chill effect: moving air rapidly cools exposed skin by evaporating moisture and removing
warm air from next to body → reduces time it takes for frostbite to form
o lower wind chill temperature is more important than air temperature in blizzards
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- ice storms: prolonged periods of freezing rain, can be more damaging than blizzards and just as
dangerous
o ice accumulates on all cold surfaces and is harmful to utility line and trees and to surface travel
- these storms typically develop during winter in belt on north side of stationary or warm front
o combination for 3 conditions leads to freezing rain
1. ample source of moisture in warm air mass south of front
2. warm air uplifted over shallow layer of cold air
3. objects on land surface at or very close to freezing
o snow begins to fall from cooled top of warm air mass
o snow melts as it passes through warm air and resulting raindrops become supercooled when
they hit the cold air at surface
o upon contact with cold objects such as roads, trees, utility lines, rain immediately freezes to
form coating of ice
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Document Summary
Blizzards can produce lengthy periods of heavy snowfall, wind damage, large snowdrifts: e. g. blizzard of 1888: killed more than 400 people and paralyzed northeastern us for 3 days with snow drifts high as second floor buildings. Na: foggiest areas are pacific, new england, atlantic canada coasts and valleys and hills of. Dense fog responsible for aircraft and maritime accidents. Drought: extended period of unusually low precipitation that produces temporary shortage of water for people, other animals, plants. More than 1 billion people live in semiarid regions where droughts are common. New mexico were at their lowest points in decades. Mountain windstorms that develop seasonally on downwind or lee side of mountain ranges and downslope of large glacial ice fields: windward is the direction upwind (toward where the wind is coming from) from the point of reference. Leeward is the direction downwind (or downward) from the point of reference.
