Wednesday, January 20, 2016

The GFS Gone Wild: Astonishing Snowstorm Forecast for the Metro D.C. Area -OR- Time for a Movie at the Knickerbocker Theatre??

**This entry was posted January 20, 2016.**

The 0Z 1/20/2016 GFS run showing snowfall forecasts for the mid-Atlantic region as prettied up by StormVistaWxModels.com.

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So by now you probably are aware that there is the potential of a major winter storm for the Baltimore/Washington corridor starting on Friday and running into late Saturday. The models have been quite consistent -- both internally and among the main ones (i.e., the GFS and the Euro, at least the deterministic versions) in showing a classic coastal storm for the U.S. East Coast, but one that drops anywhere from 1 to 2-1/2 feet of snow right on the immediate Metro and Baltimore areas.

The 18Z Jan. 19, 2016 GFS showing precipitation type and amount and MSLP valid at hour 84 / 6Z (1AM EST) Jan. 23, 2016 for the northeastern U.S., as prettied up by WeatherBELL Analytics.

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What's more, the latest GFS run -- the 0Z 1/20/2016 -- is nothing less than astonishing 30 inches of snow for KDCA itself, which if it verified -- a MONSTER "IF" -- would break the hitherto seemingly forever unreachable pre-KDCA Washington, D.C., record of 28.0 inches recorded in the infamous "Knickerbocker Storm" of Jan. 27-29, 1922.

The KDCA 180-hour cumulative precipitation graph from the 0Z 1/20/2016 GFS.

Using a 10:1 snow-to-liquid ratio, that's 30.7 inches of snow in the event in question. (The rain part comes in a subsequent system.) That is not something that really ever happens around here and thus is hard to believe, esp. in the absence of concurrence by the Euro model and by subsequent GFS model runs.

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Another version of the 0Z 1/20/2016 GFS run showing snowfall totals for the northeastern quadrant of the United States valid through hour 180.

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The same run also shows an incredible 38 inches for KIAD and a still-paralyzing 24.5 inches for KBWI, making for the greatest and fifth greatest snowstorms of all times, respectively, for both locations. (For more info on the region's biggest snowstorms, see this informative LWX webpage.)

The KIAD 180-hour cumulative precipitation graph from the 0Z 1/20/2016 GFS.

Using a 10:1 snow-to-liquid ratio, that's 38 inches of snow in the event in question.

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The KBWI 180-hour cumulative precipitation graph from the 0Z 1/20/2016 GFS.

Using a 10:1 snow-to-liquid ratio, that's 24 inches of snow in the event in question. (The rain part comes in a subsequent system.)

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Just for fun, here is a map of how much snow fell during the Knickerbocker Storm of Jan. 1922:

Knickerbocker Storm snowfall totals across the Baltimore/Washington region.

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Having said all of this about a possible historic snowstorm, I am in a bind between not wanting to jump the gun -- as I idiotically did during the "snowquester" debacle -- and instead keeping in mind that these would-be East Coast blockbuster snowstorms can and frequently do fail to pan out in the immediate D.C. area (for a variety of reasons), but on the other hand, recognizing the potentially historic nature of this storm.

And even when KIAD and KBWI have gotten 2+ feet of snow, KDCA (in the modern airport era) has almost invariably come in far below that -- in the 14 to 16 inch range.

Left: 850mb pressure, 6-hr precip., and MSLP valid at hour 87 / 15Z Jan. 23, 2016 from the GFS 0Z Jan. 20, 2016.

Indeed, when I looked at the animated loop of the 850mb 0C line and placement of the coastal low with respect to D.C. in tonight's 0Z run, I figured the MOS numbers associated with this GFS run,  but they did not. Instead, they show all snow here.

Keep in mind that the 12Z Euro on Tuesday had backed off somewhat on the amounts, and in terms of what is happening in the real world, the actual culprit piece of energy that will give birth (through momentum and vorticity transfers to the coastal low) is only just now reaching the Pacific Northwest and has to transit the entire Lower 48 United States.

Having said that, the forecasted storm itself is -- as Paul Kocin says in one of the linked CWG entries below -- a textbook case with all the ingredients you need. I'm not going to go into that right now.

In short, it all remains to be seen -- but the panic button is almost certainly to be hit starting tomorrow in earnest.

In the meantime, I direct you, the interested reader, to a series of Capital Weather Gang entries (links embedded)* (as well as the thousands upon thousands of comments, though those can easily be ignored):

Overnight forecasts support severe late week snowstorm threat by Jason Samenow

How much snow are the models actually forecasting? by Jason Samenow

Weather Service: "Textbook" East Coast snowstorm could resemble all-time greats by Jason Samenow


The key characteristics of Washington's biggest snowstorms by Ian Livingston and Jordan Tessler

Confidence growing for major winter storm this weekend, but it's not a lock by Wes Junker

*Of note, you are limited in the number of monthly visits to the WaHoPo.com site, although I manage to avoid that by simply clearing out my Chrome history (I only go to the WaHoPo.com site with Chrome), but that might be because my internet access is through my work computer and my work system uses different proxies.

Also note that the entry titles sometimes change while the URL does not.

Anyway, at this point, I would assume that Sterling LWX should start issuing watches for our area by late tomorrow.

In the meantime, I am signing off for now. I'm uncertain when my next update on this will be -- but as circumstances warrant. However, I will not be home tomorrow evening until later.

--Regulus

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