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PA, WV Plummet to Teens

By Jesse Ferrell, AccuWeather meteorologist and senior weather editor

Published Nov 4, 2006 3:32 PM EDT | Updated May 21, 2008 4:52 PM EDT

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UPDATE: The following readings below 20 in PA are hereby added. These were NWS COOP stations which didn't come in until later Saturday:

South Mountain: 19
Mount Davis: 19
Montrose: 19
Laurel Summit: 19
Wolfsburg: 18
Confluence: 17
Philipsburg: 17
Everett: 17
Prince Gallitzin: 16
Huntingdon: 16
Ebensberg: 15
Meyersdale: 14
Clarence: 14

UPDATE: The following record lows were set on Saturday:

NEW YORK CITY (KENNEDY), NY (34)
MACON, GA (26)
COLUMBIA, SC (26)
ROANOKE, VA (24)
SALISBURY, VA (23)
READING, PA (23)
DANVILLE, VA (22)
ASHEVILLE, NC (21)
LYNCHBURG, VA (21)
TRI-CITIES, TN (21)

ORIGINAL POST:

The coldest air of the season moved over the mid-Atlantic last night, dropping temperatures into the teens in parts of Pennsylvania and West Virginia. I was surprised by how cold it got locally. Here in State College, PA,the NWS [JessePedia] was predicting "lower 20s" here and I believe AccuWeather was saying 24. At the airport, which dipped only to 24, that forecast verified. But in selected areas, it was much colder. At my house, I dipped to 15.6 degrees this morning.

Looking at the surface weather maps, it was clear that the coldest air in the eastern United States was in Central Pennsylvania and central West Virginia, with both states seeing temperatures as low as 14. Why?

Often you have a high pressure system driving cold air from Canada down into the Appalachians. But in that case, you'd see cold temperatures FROM Canada TO the Virginias. Looking at the surface weather map from this morning, the reason is clear:

A high pressure system is planted over those states. What does this do? It gives two key ingredients to cold temperatures. First, it clear skies so that heat radiates away from the Earth. Second, it calms winds. Winds cause mixing of air, regulating temperatures near the surface. This is easy to see at my weather station. The graphs below are from last night. Notice that every time the wind increased, the temperature went up (yes, the sun also helped after 7 am).

But back to what I was saying. Check out the wind map from this morning:

The black area over WV & PA show winds of less than 5 mph (pretty much calm). That matches the location of the high pressure system, and the location of the coldest temperatures.

The Forecast Models [JessePedia] didn't predict the lowest temperatures either. This may simply be due to the resolution of the models, or they could have misjudged the calm winds. The NMM Model doubted any temps below 25 degrees at "2 meters," which is where "surface" temperatures are measured officially, and (presumably) where the temperature list below came from. Even at ground-level, it wasn't convinced of 15 or lower (notice that it recognizes the warm water over the Great Lakes, cute). And even the high-resolution WRF model didn't foresee anything below 23 in Pennsylvania.