Understanding Pennsylvania Snow
The 60th anniversary of the Great Ice Storm of 1950 passed not long ago and is a great time to again reflect on momentous winter storms here in Central Pennsylvania. (The Altoona Mirror's Mark Leberfinger wrote an excellent feature on the 1950 storm in November 2010.)
Snow and ice storms can be curious and complicated things. Why does it snow when and where it does? A great place to look at the factors influencing snow is right here in Pennsylvania. The range of snowfall in the Commonwealth is astounding, Philadelphia averaging only 20 inches while the snow belt in the lee of Lake Erie gets 100 inches annually. While we here in Central Pennsylvania seldom get a big snow before Christmas, the Northwest can be pounded by lake-effect snow that gathers moisture from the still-liquid lakes starting as early as mid-October.
Elevation’s impact on snowfall totals can be seen right here in Blair and Cambria Counties. Average snowfall in the valleys near Altoona’s elevation is about 40 inches per year, while places just west of us on the Allegheny Plateau in Cambria County (nearly 1,500' higher) get over 60 inches.
All this talk about averages, however, ignores the fact that many winters depart from the norm a great deal. In light of 2010's above average snowfall, it is fun to look at the biggest snowfalls we’ve ever had. The total snow pack, drifting and road conditions can all warp our perception of how much snow we really have.
It turns out that in the 75 years from 1926 to 2000, Altoona has officially had only 45 snow events of ten inches or more. (We defined a snowstorm as any one, two or three day period with ten inches or more of snow accumulation.) Five different times (1941, 1964, 1970, 1971, 1972) we had two such storms in one winter. Twice (1978 and 1994) we had three in the same snow season. That means that more than half our winters have not even had a double digit storm.
Our twenty inch storm in 2010 was only the ninth storm of such magnitude since 1925. Only one was officially over two feet, the March 6-7 blizzard of 1962 that brought us 26 inches. Our second biggest was perhaps our most unlikely, a 23 inch fiasco on April 27-29, 1928.
One of the worst weeks of snow in our local weather annals came when 35 inches fell from three separate storms January 14-21, 1978. The seventies, in fact, had more double digit snowstorms than any decade on record.
As you might have expected, well over half our biggest storms were in January and February. March, however, nearly matches the colder months. As a battleground of winter and spring weather, March can provide everything you need for a potent storm - abundant moisture from the Gulf and the Atlantic, coupled with the last gasp of cold winter air.
All this does not necessarily mean that all December's have light snowfalls or that all Marches are snowy. After all, the one thing we can say for sure about snow is that we don’t know what to expect from one year to the next.