Thursday, December 16, 2004

Now this is what we mean by a real winter kickoff...
DECEMBER 2004 WINTER SOLSTICE SNOWSTORM



FIRST SIGNIFICANT SNOWFALL OF THE SEASON FOR I-95 CORRIDOR
TO BE A 36 HOUR EVENT BEGINNING SUN AFTERNOON UNTIL MON NOON

Computer models have aligned on the likelihood of the first major East Coast storm to develop along the VA/NC border Sunday afternoon. A fresh recharge of Arctic air will be moving toward the Northeast as the storm develops. This new supply of air will enable our anticipated storm to deepen rather quickly Sunday night, and allow for windy and snowy conditions from eastern Virginia northward to Maine. Compared to similar arrangements in previous winter patterns such as the one we're in now, this has the potential to become a SUPERSTORM much like the March 1993 Storm of the Century, but it's overall impacts will be limited to the Mid-Atlantic and New England. More later about why that is possible.

Foot's Forecast makes this call for the following total storm accumulations:
This is based on a detailed analysis of the 1:15 water-to-snow ratios expected due to cold air filtering into the storm overnight Sunday into Monday. Remember all you Earth Science folk out there... 1 inch of liquid is 10 inches of snow at 30 degrees, the colder the upper air temp, the more snow you can squeeze out of the same portion of the atmosphere

2-5" in the DC-Baltimore Metro regions for Sunday night into Monday.
4-8” in Central PA and Western MD mountains due to influence of lake effect snow
4-8” in southeastern Pennsylvania from the Philly suburbs northeast to NYC.
6-12” in NYC suburbs and interior New England

(this might be an underestimate if what forecasters are thinking about this storm comes true)

Accuweather forecasters are saying on restricted public access sites (which I pay to view) that most computer models have come into agreement on this developing storm situation, and have already begun to advise their major corporate clients across the East Coast on planning ahead for the resulting cold and snow.

So you Powderhounds, rejoice. And with the arrival of this system on the eve of the change in seasons, I predict it will become known as the "Winter Solstice Snowstorm of 2004." This event does have the potential to evolve into a Superstorm later in it's lifespan, but NOT for the DC-Baltimore region, as snowfall will be limited south of Philly because the storm is projected to develop along the Virginia coast and then move north. That means New England will get eventually clobbered, while everyone from DC north and east gets maybe isolated pockets of 6 inches, with an overall 2-5" spread.

SO WHAT ABOUT SCHOOL?

Metro Baltimore and DC: Rain changing to snow Sunday, and falling temps overnight Sunday, with a on-going snow event Monday morning 12-20 is enough to close schools. Plows will have ample time to clear the snow as comes to an end Monday afternoon, thus schools will be OPEN on Tuesday 12-21. Lingering flurries and light snow will dot the area into Tuesday.

Philadelphia and suburbs (Chester, Delaware, Montgomery): The farther north and east, the heavier accumulations are anticipated. With a potential of 6" or more, I expect all PHL public and parochial schools, as well as most suburban schools to close Monday 12-20, but reopen Tuesday. In some rural areas where total could exceed 8 inches in isolated spots, perhaps a 2-hour delay on Tuesday. Very wind and very cold. Highs in the 20's Tuesday.

Central PA: Probably a delay on Monday, depending on how quickly the lake snow machine kicks in and interacts with the eastern snow.

New York City: Delays are likely, but it takes a lot more than 6” to close all NYC schools.
But this is a powdery snow, not wet. Winds whipping through the cavernous city will create temporary whiteout conditions.

Boston: Rain at first, then change over to snow as storm lifts north and axis tilts westward. More likely you'll miss school on Tuesday.

Interior New York and New England: You're used to big snow, so fuggetaboutit. Although it will be bitterly cold with highs in the teens and wind chills well below zero.

HOW CAN YOU PREDICT ALL THAT?

The timing of the snowfall is critical when considering if schools would be closed. In the Baltimore and DC metro region on Sunday afternoon, rain and snow will wet the ground. Slightly warmer conditions Friday and Saturday will have allowed the atmosphere to moisten a bit before the storm arrives. So as pointed out by my astute colleague Mr. Henry, it will not take as long for the “column to get saturated” which is a requirement for the snow to reach the ground.
If upper air levels already have a high relative humidity, it wont' take much for the air to reach saturation at cloud level. Factor in some evaporative cooling, which is an effect that cools the atmosphere as moisture converts to snow, and surface layer temps begin“falling with the snow.”

When overnight surface temps fall into the upper 20's...icy road conditions will result. On top of that slight ice layer will be another 2-3" of snow by Monday morning, and snow will continue to fall through the morning. This presents an unsalvageable situation for school officials, as a decision on whether to keep a 2-hour delay in place or change to closing would have to be made at approximately 6:45 AM. It will likely still be snowing at a moderate pace by then, which seals the deal for all those out there in schoolhouseland.

Combine all this with another surge of Arctic air behind the storm thanks to the counter-clockwise wraparound effect, and it will be a wind-whipped, snowy, Christmasy kinda time for everyone.And there's another one in the offing for Thursday-Friday, and this will spell White Christmas for much of the eastern half of the U.S. And behind that is even more cold and snow that will make this little clipper look like a flurry. It's beginning to look a lot like winter, finally.

SITE UPDATES:
During developing storm events, this site is updated around 6AM daily, then again at 6PM. Once we get into official storm mode (Watches and Warnings issued by NWS) updates occur at 6AM, 4PM and 9PM. The next regular update will be at 9pm Thursday.

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