Early Season Snowstorm set to hit Northeast

Winter Storm Watches extend from the mountains of Virginia to the coast of Maine in advance of this October storm. This map is from 12:15PM EDT on 10/28/11.

October snowstorms are not unheard of in the US, but they are a bit surprising.  Most locations in eastern US average less than an inch of snow during the month, indicating that snow is not the year-to-year norm.  A few inches one year and maybe they won’t see snow again for another 10 years in October.  But 6 inches? 10 inches?  That is a lot of snow for October, especially when leaves are still on trees and people have yet to put on a costume for Halloween.

Much like the event in Denver two days ago and the snow across New England last night – this is expected to be a heavy, wet snow.  Temperatures are still relatively mild for snow, which results in snow ratios around 6:1 (6 inches of snow for every 1 inch of liquid water).  I wouldn’t be surprised if the ratios are lower than that.

The Good News

It’s not December, January, or February.  If it was, the cold air would be much deeper from the surface up through the atmosphere.  Temperatures could easily drop below freezing and this would be an all-snow event for much of the east coast.  Furthermore, snow ratios would be much higher (on the order of 10:1), leading to snowfall totals well over a foot and approaching two feet in many locations.  That would completely shutdown the area for a few days.

As it is, warmer temperatures will result in rain at the outset for almost everyone in the path of this storm and rain will be the primary precipitation type in the heavily-populated areas near I-95.  Where it does change over to snow, temperatures at the surface should hover around freezing, which will help keep roads clear of snow and merely wet.  Accumulations will be kept down because of the warm ground and low snow ratios.

Another bit of good news is that the weather should warm up in the few days following this storm, allowing for the snow to melt away.

The Bad News

The heavy, wet snow, combined with strong winds, will undoubtedly lead to tree branches snapping off and coming down on power lines.  Last night, power was lost for many in southern Vermont and New Hampshire as power lines came down.  In some cases, those power lines triggered fires.  Also, because the areas most affected by this storm are relatively rural, it may be difficult for power to be restored quickly.

Travel may be hampered for a short time, especially across the higher elevations in the Appalachians.

The Scary News

There is still a lot of uncertainty with this storm.  For example, look at NOAA’s probability map for at least 2 inches of snow ending 8AM Sunday morning:

NOAA's forecast probability of at least 2 inches of snow over a 24-hour period ending 8AM 10/30/11.

There’s about a 50% chance that DC, Baltimore, and Philly see at least two inches of snow.  But if this morning’s GFS is correct, it will be predominately rain in these areas with snow mixing in at the end.  Just a slight variation in the track of this storm could be the difference between a rainy Saturday and a snowy mess.

Accumulation Guesses

You want ’em… you got ’em:

From Accuweather.com

From Joe Bastardi at WeatherBell. In case it's tough to read, the lightest shading is 1-3 inches, locally 5. Next shading is 3-6, locally 10. Darkest shading is 6-12, locally 15.

From The Weather Channel and Weather.com

If I have to pick one to go with, I’ll side with The Weather Channel, but I reserve the right to change my mind when I’m wrong. 🙂

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