Monday, January 20, 2014

A Suddenly Potentially Snowy Forecast -OR- SREF KDCA Total Snow Plume You Up (UPDATED)

**UPDATED 9:41AM, 9:58AM, and 1:34PM 1/20/2014: See below.**

The 21Z (5PM EST) 1/19/2014 SREF plume diagram for KDCA (National Airport) total snow through 12Z 1/23/2014.

UPDATED 9:58AM: I had to update the name of this image due to my mixing up of the model run time and the date. I also added a title and inches of snow numbers on the side for clarity.


OK, something potentially significant is going on weather-wise for Washington, D.C. -- and I KNOW that I'm going to regret writing this when we get "TRACE" / flurries / nothing. However, and except-o in this case, even if it doesnt' snow, I shall be heading to Buffalo / Niagara Falls next weekend with Gary to see some actual snow.

Anyway, the 0Z 1/20/2014 "deterministic" GFS model shows a 3 to 6 inch snowfall event at KDCA (Reagan Washington National Airport). The 0Z NAM and latest 6Z 1/20/2014 NAM show similar ranges.

More to the point, the 21Z (5PM EST) 1/19/2014 SREF plume diagram for total snow at KDCA has in the 4-day run (primarily through 18Z (1PM) 1/22/2014) amounts on the 23-member ensemble ranging from 2.26 inches minimum (MBP1) to a mean of 10.04 inches to an absurd maximum of 33.08 inches (ARN2), and six of the ensembles are over 15 inches of snow.

Just sayin' ...

The updated 3Z 1/20/2014 (10PM EST 1/19/2014) run has a max of 23.46" (ARN2) and a min of 0.71" (NMP1) but the mean is about the same at 10.40" of snow.

I suspect there will be a winter storm watch in place at some point later this Monday. I'm sure I'll have more to say about this -- one way or the other.

Updated 9:41AM 1/20/2014: So Sterling LWX has issued a winter storm watch for nearly its entire county warning area (CWA) including all of Metro D.C. and Metro Baltimore. Furthermore, other adjacent forecast offices have issued similar watches for much of their CWAs including Mount Holly / Philadelphia (PHI), Wakefield (AKQ), and Blacksburg (RNK).

Sterling (LWX) CWA webpage showing weather advisories in effect as of 9:25AM 1/20/2014.

The dark blue color is a winter storm watch for 5" or more of snow.


The latest SREF KDCA plumes (9Z 1/20/2014) backs off on the high end -- 19.01" max (ARN1) -- but the mean is still ends up at 9.16".

A broader view of the NWS Eastern Region weather advisories in effect as of 9:31AM 1/20/2014. Again, the dark blue color are winter storm watches for portions of the various forecast offices' CWAs.

For much more information including snowfall ranges and probability tables, see the LWX Winter Weather Page. Oh, and of course, the Capital Weather Gang site.

End of update.


Update #2 1:34PM 1/20/2014:

Current Sterling (LWX) CWA and adjoining NWSFO CWA advisories in effect as of 1:19PM EST 1/20/2014. The hot pink / magenta is a winter storm warning.

Don't let the fact that it is nearly 60F at KDCA fool you -- there is a strong Arctic boundary approaching, presently located about 300 miles to the NNW across northwestern Pennsylvania.


Sterling has upgraded much of its CWA to a winter storm warning starting tomorrow morning at 7AM. It appears as though 2 to 4 inches is a certainty and 4 to 6 inches is quite possible in the D.C. and Baltimore areas. There is also a chance of greater than 6" but that is contingent on heavier snow bands setting up.

Snow forecast map for the LWX CWA generated at 1:20PM 1/20/2014 and valid through 1AM 1/22/2014. It's a general 4 to 6 inch total.


What is happening -- and I should have mentioned this originally -- is a clipper system is riding down a northwesterly flow behind an Arctic front progged to move across the mid-Atlantic this evening. The clipper system is forecasted to rapidly intensify along this Arctic boundary as it is energized by favorable synoptic dynamics and highly favorable Gulf Stream thermodynamics. It should really intensify once offshore as these storms tend to do. The low, while not incredibly strong as it crosses the mid-Atlantic, will impact the entire Richmond-to-New York City I-95 corridor for a number of hours because of the fact the fact the system will be rounding an upper level trough over this region as the deepening shortwave takes on the all-important negative tilt.

Screenshot on the LWX Winter Weather Page of "Chance of Snow Accumulation" for the Jan. 21st, 2014 event for select locations -- showing ranges and accompanying probabilities.

End second update.


I had a nice night tonight -- first, briefly, at Nellie's; then on a bike ride that took me past the White House and down to the Lincoln Memorial; and then back up to Larry's Lounge, where I met Gary. He was back from Aruba (and brought me a little flag). I also met Jim, who stayed an extra day before returning to Milwaukee.

All in all, it was a good night.


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