Significant Snowfall Likely Parts of Mid-Atlantic/Northeast

[donsutherland1]

Based on a combination of the latest synoptic pattern and the model consensus by the ECMWF (until tonight), ETA, and GGEM, it appears that the northern Mid-Atlantic region and Northeast will likely experience a significant early December snowstorm for the second consecutive year.

<b>Note:</b> These figures are for the second storm only (I added this note due to confusion that resulted; December 6-7 refers only to the second event, which I believe will be the larger event).

<img src="http://wintercenter.homestead.com/files/120502-8.jpg">

Snowstorm of December 5-6, 2003 (Larchmont, New York)

For those who are interested, a brief summary of some of the key ingredients for big East Coast snowstorms follows.

<b>Brief summary of key factors for such snowstorms:</b>
• <I>Upper-level trough/ridge pattern:</I> Provides source of vorticity and kinetic energy, upper-level divergence, and associated ascent. Amplification of this feature often marked by decreasing wavelength, increasing amplitude, and the development of diffluence downwind of a ‘negatively tilted’ trough axis.
• <I>Upper-level jet streaks:</I> Increase upper-level divergence, kinetic energy, and vorticity. Combination of jet streaks could be an important factor in juxtaposing different air masses and enhancing ascent patterns required for heavy snows.
• <I>Cold anticyclone extending across the eastern Great Lakes, southern Canada, or New England north of the incipient low:</I> Provides cold air required to maintain snow along the coast, a process augmented by cold air damming east of the Appalachian Mountains (19 of 20 major snowstorms studied by Kocin and Uccellini).
• <I>Low-level jet: </I>Increases the transport of moisture into region of heavy snow, warm air advection, and associated ascent pattern. Plays a possible rule in focusing mass-flux divergence during cyclogenesis along the coast.
• <I> Latent heat release:</I> Provides extra heat for intensifying cyclogenesis through the self-development process.

<b>Source:</b> Paul J. Kocin and Louis W. Uccellini, <I>Snowstorms Along The Northeastern Coast of the United States: 1955 to 1985</I>.

It is also important to note that as a general rule, based on a number of case studies, whenever the relative humidity at 700 mb is greater than 80% <I>and</I> there is forcing, precipitation is likely. Under such a scenario, more forcing leads to more precipitation.

<b>Early-Season Snowfall Can Have Important Implications for the Winter:</b>
A big early-season snowfall of 6” or more prior to December 7 can have major implications for the upcoming winter and certainly break the proverbial back of fears that suppression will lead to a snow drought for the upcoming winter. In such cases, while there can be suppressed periods, winters as a whole are not “suppressed” in general with regard to their storm tracks.

New York City's significant early-season significant snowfalls (December 7 and earlier) are as follows:

November 24-25, 1938: 8.8"
November 29, 1882: 9.0"
November 30, 1898: 6.0"
December 4, 1957: 7.5"
December 5, 1886: 8.1"
December 5, 2002: 6.0"

In all six winters, seasonal snowfall was above to much above average for New York City.

Total winter snowfall for these seasons:
1882-83: 44.0"
1886-87: 32.9"
1898-99: 55.9"
1938-39: 37.3"
1957-58: 44.7"
2002-03: 49.3”

Average: 44.0”

In addition, for those living in the Mid-Atlantic region, in 3 of the 4 years since regular recordkeeping began in Washington, D.C., snowfall was above 25" there. Only 1938-39 (13.6") came in with below normal seasonal snowfall.

At the same time, an especially snowy December (12” or more)—and if the upcoming storm dumps as much as some of the model guidance suggests is possible, it will put December 2003 on a “fast track” toward such snowfall—offers a strong signal both in Boston and New York City of above normal snowfall for the coming season:

In Decembers in which total snowfall came to 12” or more:
• 14/22 (63.6%) seasons saw more than 50” for the season and 17/22 (77.3%) saw more than 45” for the season in Boston.
• 14/15 (93.3%) seasons saw 30” or more for the season in New York City. The average came to 44.7%. Lowest: 28.7”; Highest: 63.2”.

In Decembers in which total snowfall came to 12” or more in both Boston and New York City:

There was a somewhat greater tendency for suppression, though both cities still saw above normal snowfall.

• 4/7 (57.1%) of seasons saw more than 45” for the season in Boston with an average of 59.0”.
• 6/7 (85.7%) of seasons saw more than 30” for the season in New York City with an average of 47.7”.

<b>What to Expect December 6-7:</b>

A combination of factors is considered for the December 6-7, 2003 event:
• Strong consistency of the ECMWF (until today’s run)
• Consensus of the ECMWF, GGEM, and ETA
• Anticipated strength of the High Pressure that will develop in the confluence of the Grand Banks vortex (suppression is not a highly likely scenario)
• Teleconnections (Spain and recurvature of Typhoon Lupit)
• Evolution of 500 mb height anomalies and North American temperature profile
• Atlantic Ocean SSTAs
• Assumption that the lead wave will not become so strong so as to inhibit development of the second wave
• A review of a number of past storms

Based on these assumptions, and recognizing continuing uncertainty (especially as hinted at by the European Model) I believe the following is likely:

<I>High Risk of 6” or More/Moderate Risk of 12” (Generally 6”-12” with locally higher amounts):</I> Albany, Allentown, Catasaqua, Danbury, Harrisburg, Hartford, Mount Pocono, Morristown, Poughkeepsie, White Plains, Worcester

<I>High Risk of 4” or More/Moderate Risk of 6” or More/Low Risk of 12” (Generally 4”-8” with locally higher amounts):</I> Boston, New Haven, New York City, Newark, Philadelphia, Providence, Spring Mount, Trenton

<I>Moderate Risk of 4” or More/Low Risk of 6” or More (Generally 3”-6” with locally higher amounts):</I> Concord, West Babylon, Wilmington

<I>Low Risk of 4” or More (Generally 2”-4” with locally higher amounts): </I>Atlantic City, Burlington, Baltimore, Washington, DC

<b>Note:</b> These figures may be conservative, but given the uncertainty that still exists, I’ll err on the conservative side for now. Adjustments can be made tomorrow.

[Heady Guy]

Those are some of the lowest, that I have seen yet. Only time will tell.

[donsutherland1]

As I said, I chose to come in on the conservative side and will adjust as necessary at some point tomorrow.

Certainly if Philly or NYC were to receive 4"-8" or perhaps up to a foot, that would be a huge early December snowfall. Moreover, the figures are for the second storm only. They do not include the amounts for the first storm.

[WEATHER53]

31 degrees.
1/3" on grass and cars. Snowed heavily from 11-11:20, light to moderate right now.

[donsutherland1]

Weather53,

Thanks for the update.

This snow is from the first event. More--though I don't believe a substantial amount--will likely occur Friday night into Saturday.

Enjoy it.

[JCT777]

Don - if your numbers are for the 2nd storm only, then they are pretty good IMO. They may need to be bumped up a little if things keep looking the way they are.

[donsutherland1]

John,

Yes, they are for the second storm only. There is the potential for more than those numbers, but I'll err on the side of conservatism until tomorrow's model runs.

[donsutherland1]

John,

I added a note into the initial post that it refers to the second event, only. I thought I had put the note in earlier but only included December 6-7 for the dates (first event got underway December 5). I hope it's now clearer for all.

[donsutherland1]

As I noted yesterday, I offered conservative figures for the second storm due to uncertainty that still existed. Given the latest computer guidance this morning, I am more confident that the ECMWF's 12Z run yesterday was an aberration.

Based on this idea, my ideas for snowfall totals are as follows:

12"-24": Hartford, Morristown, Poughkeepsie, Worcester
8"-16": Allentown, Boston, Catasaqua, Concord, Harrisburg, New Haven, New York City, Providence, White Plains
6"-12": Philadelphia
4"-8": Baltimore, Wilmington

[JCT777]

Don - if your updated numbers are just for the 2nd storm, then I think you are 100% correct. A great snow event for all from DC through Boston!

[donsutherland1]

John,

That's correct, they are for the second storm, only.

I forgot to put DCA's updated figures: 3"-6" there for the second storm.