UPDATE: We now have an official, updated accumulation map for this storm in our news story. Keep an eye on that for updates.
We proved here in State College in 2009 that heavy wet snow on top of trees with leaves can cause large numbers of downed trees and power lines. The big question for this weekend's snow in the Northeast is: How disruptive will it be? How much damage will be caused? Will this add insult to injury for Hurricane Irene-damaged areas?
The answer depends on the accuracy of the three maps, and where they correspond. The first is our snow map (as of Thursday morning, click here for latest version):
The next map to consider is one showing the amount of leaves on the trees. FoliageNetwork.com says that these are the conditions, as of yesterday (October 26):
Another consideration is whether the area has seen mass tree damage recently -- and of course part of it did, during Hurricane Irene. These are the official reports of tree damage and high wind reports from the two days surrounding Hurricane Irene, but I was in York, PA for the storm so you'd might as well fill in the area to the south of Harrisburg.
These maps seem to say that (northeast of Maryland anyway) the worst of the snow will correspond with the area that still has the most leaves, but which already had weak trees knocked down by Hurricane Irene. Assuming these maps are accurate, this storm will certainly add insult to injury for the area that was damaged by Irene, but if she already took out the weak trees, it might not be as bad as it could have been. But where might the *worst* damage occur?
The most likely area to take on severe damage from this storm is north-central Maryland and the Virginias, where elevation may be low enough that the leaves have already fallen, and where no damage was caused by Hurricane Irene. To the Northeast of there, other low-elevation places that weren't damaged by Irene could be at risk too.
Of course, any adjustment in the forecast snow swath, or inaccuracies of these maps, could spoil this forecast, so we'll have to keep an eye on things through the weekend. But if I lived in Winchester, VA, Frederick or Hagerstown, MD, I'd have a generator on hand this weekend.
UPDATE: We have extended the snowfall in the map above down into the NC mountains -- so areas in the southern Appalachians that still have leaves are now also at risk.
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