TYPES OF HEAVY SNOW EVENTS WHICH IMPACT PENNSYLVANIA
Heavy snow can immobilize a region and paralyze a city, stranding commuters, closing airports, stopping the flow of supplies, and disrupting emergency and medical services. Accumulations of snow can cause roofs to collapse and knock down trees and power lines. Homes and farms may be isolated for days and unprotected livestock may be lost. The cost of snow removal, repairing damages, and the loss of business can have severe economic impacts on cities and towns.
Heavy snow can be produced by nor’easters, blizzards and overrunning situations. Lesser amounts of snow are often produced by Alberta clippers.
- Nor’easters are intense areas of low pressure that typically develop along the eastern seaboard most often during late fall, winter and early spring. They usually bring strong northeast winds to areas near the coast as they move north along it. Some memorable nor’easters in recent years included the President’s Day snowstorm of 2003, the February 11th and 12th storm of 2006, the Valentine’s Day snowstorm of 2007 and the snowstorm of February 25th and 26th, 2010. Snowfall rates in nor’easters can reach 2 to 4 inches per hour and these rates can last for several hours.
- Overrunning can also produce heavy snow. This occurs when warm air aloft flows over cold air near the surface. Overrunning happens mostly during the winter when the contrast in airmasses is greatest. Overrunning occurs most often when a large dome of high pressure is located in southeastern Canada and a warm front is approaching our region from the south or southwest.
- An Alberta clipper is an area of low pressure that usually develops over the province of Alberta in Canada, east of the Rocky Mountains. Alberta clippers usually move very quickly southeast from their point of origin and usually bring only light snow as they cross our region unless they intensify off the east coast. They also allow colder air from Canada to move into our region in their wake.
Some snow terms which are commonly used include blizzard, blowing snow, snow squalls, snow showers and snow flurries.
- A blizzard is a winter storm which has sustained winds or frequent gusts of 35 mph or more, with considerable falling and or blowing snow frequently reducing the visibility to at or below one quarter mile, and these conditions last for 3 hours or more. Some of the greatest snowfalls on record in Pennsylvania occurred during blizzards. 1 to 2 feet of snow fell over a large part of Pennsylvania during the blizzard of 1993.
- Blowing snow is wind driven snow that reduces visibility. Blowing snow may be falling snow or snow already on the ground that is picked up by the wind.
- Snow squalls are brief intense snow showers accompanied by strong gusty winds which may produce significant snow accumulations.
- Snow showers have snow falling at varying intensities for brief periods of time with some snow accumulation possible.
- Snow flurries are light snow which falls with little or no snow accumulation.