Heavy accumulations of ice can bring down trees and powerlines, as well as topple utility poles and communication towers. Ice can disrupt communications and power for days while utility companies repair extensive damage. Even small accumulations of ice can be extremely dangerous to motorists and pedestrians. Bridges and overpasses are particularly dangerous because they freeze before other surfaces.
Freezing rain is the result of precipitation which initially falls as snow, then encounters a layer of warm air which melts the snow changing it to rain. The rain then freezes as it encounters below freezing air at or near the surface creating a film of ice.
Most of the United States receives less than 10 hours of freezing rain annually with the highest frequency in the Saint Lawrence River valley where over 40 hours of freezing rain are observed annually.
The national weather service issues ice storm warnings for Pennsylvania when significant ice accumulations are expected and winter weather or freezing rain advisories for any ice accretion which also includes freezing drizzle. The Poconos in northeast Pennsylvania are most susceptible to ice storms with the most recent storms occurring in January 2003 and 2005.