Types of Storms that Typically Produce Heavy Snow in PA |
OverviewThe heaviest snows in Pennsylvania typically come from "Lake Effect," "Nor'easters," "Alberta Clippers," and "Squall Lines." If you click on the thumbnail images you can see the full-scale image (below). * Lake EffectLake Effect snow is generated when very cold air moves across the Great Lakes and picks up extra moisture and warmth from the relatively warmer lakes. This process can be slowed or stopped if the lake(s) freeze over. Lake Erie is normally the only Great Lake (excepting Lake St. Clair) which will freeze over almost entirely by the end of the winter. However, when there is open water, the added warmth and moisture create shallow convection and snow showers, known as Lake Effect snow. * Nor'eastersA Nor'easter is a storm characterized by a central low pressure area that deepens dramatically as it moves northward along the U.S. East Coast. The name came from the strong northeast winds that precede and accompany the storm as it passes over New England. Nor'easters are notorious for producing heavy snow in the Central and Northeastern Mountains (including the Poconos), but typically make lighter snow (or even no snow) for counties in the west. Nor'easters will usually produce a heavy, wet snow. There is usually a fairly consistent demarcation between rain, mixed precipitation, and snow which moves along with the storm and generally parallel to the track of the surface low. The demarcation typically pivots with the storm as the track changes direction. The mixed precipitation and rainfall are generated when warmer marine air is pulled into the storm. The heaviest snow in a Nor'easter falls to the north and west of the track of the surface low.
* Alberta ClippersThe other typical snow-producer for PA: Alberta Clippers (or "Clippers"). * Squall LineA more-unusual snow-producing weather system would be a "Squall Line" along a distinct cold front, or trough of low pressure at the surface, which moves through with relatively cold air already in place. The squalls will usually be at the very leading edge of very cold air masses, and to the south of a larger shield of snow. These squall lines usually have a strong upper-level cyclone driving the front and can generate instability. This instability leads to convective snow showers much like thunderstorms happen in the summer. Only these winter snow squalls are much more shallow/shorter than summer thunderstorms. These intense squall lines resemble the heaviest lake effect bands in width and intensity, but move steadily west to east, and pack strong winds as they move through. ** CaveatsElevation will almost always play a role in how much snow/ice each location will receive in these storms. Trying to time precipitation changes is very difficult due to the uncertainty of the surface low track, and therefore the thermal characteristics of the 3-dimensional storm. Many early- and late-season storms will only produce snow in the higher elevations of the state, since the air in the valleys is too warm.
** Seasonal Totals and Snowfall Averages/NormalsYou can find a seasonal normals/averages map under the "Snowfall Info" tab on our https://www.weather.gov/ctp/moreWater page. Under the "Seasonal Normals" section of the Snowfall Info tab, you can find instructions on how to pull snowfall normals for specific places directly from the database for individual observing locations. GLEN HAZEL 2 NE DAM (363311) Monthly Totals/Averages Snowfall (inches) Years: 1971-2001 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Season Average 0.0 0.0 0.0 0.2 6.5 17.4 19.0 13.7 12.0 2.2 0.1 0.0 71.2 |
"Lake Effect":
"Miller Type-A":
"Miller Type-B":
"Alberta Clipper":
"Squall Line":