The Coming Halloween Superstorm -- or Not

UPDATE: 10/23: Our map has been updated as shown below. Additional models are predicting a large East Coast storm next week. I can't guarantee that I'll have time to keep up with it all on this blog, but follow the official AccuWeather.com news story, and my Twitter & Facebook feeds for pointers to great discussions, like this cool model ensembles map and "meteorologist roundup" (in which this blog is quoted) from Capital Weather Gang.

UPDATE: 1 PM: The track map in our official news story gives two solutions, neither of which predict landfall, but one which moves the storm up the coast not unlike Wilma 2005.

MONDAY AM: The AccuWeather meteorologists (and, indeed, the entire meteorological community on the Internet) are abuzz this morning with the possibility of a large hurricane moving into the mid-Atlantic states, resulting in heavy snow inland. Before you discount the models which are predicting this (in front: The "Euro" model, demonstrably the most accurate), remember that this has happened before, with Hurricane Wilma in 2005 when it (almost) merged into a nor'easter and moved up the East Coast causing 74-mph wind gusts at the Jersey shore and over 20 inches of snow in the mountains. I was just a young blogger then:

- Oct. 23, 2005: The Perfect Storm II?- Oct. 24, 2005: Superstorm 2005 In Progress- Oct. 25, 2005: Super or Not, It's Got 28-Foot Waves- Oct. 26, 2005: Nor'easter / Wilma's Greatest Hits

And as far as a storm (any storm) causing heavy snow in the Northeast, that's becoming less and less unprecedented -- it happened here in Central PA in mid-October 2009 and again last year with "Snowtober" (30 inches of snow & 69-mph wind gusts). A high-elevation snow forecast was issued in mid-October 2010, but it was a swing and a miss. In 2008, the GFS promised us a significant storm 10 days out, but it under-delivered. something similar happened in 2007 and 2006.

So what about this year? The models have been saying some incredible stuff, like a Category 3 (sub-950mb pressure) hurricane making landfall on the New Jersey coast (ECWMF, 00Z). Because of the cold air already in place, this would bring nearly 40 inches of snow to the highest mountain tops in Pennsylvania! The less-accurate model (GFS, 00Z) keeps the storm out to sea, but there's enough cold air in place this week to have snow (at elevation) in New England even if the hurricane skips us and a front passes through, according to the DGEX model (06Z). As Henry points out, some of the NAO index members are forecast to dip low, which is another good sign that the Northeast could be in for snow next week.

In the end, only time will tell. If this does happen (even a mild version of it), this will be three out of four years that we've seen significant snow in October here in Pennsylvania.