Tuesday, March 20, 2018

Impending Mid-Atlantic Sloppy Winter Storm on the First Two Days of Spring: Overview, Forecast, and (Cranky / Not Cranky) Snow Total Maps

**This entry was posted March 20th, 2018.**

Central Park in New York City on a snowy day in December 2017; Photo by Jacqueline Clair and posted on her blog in this entry.

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Expected snowfall for the Sterling (LWX) county warning area (CWA), 10PM March 19th - 8PM March 21st, 2018.

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So the whole "DMV" region -- Maryland, Northern Virginia, the District of Columbia to include the Metro D.C. and Baltimore areas -- are under a winter storm watch (for while the northern and western suburbs are also under a winter weather advisory (for tomorrow) with the winter storm watch in effect for midnight through 8PM March 21st -- yes, the first full day of astronomical spring (which begins March 20th) -- as a complex weather scenario involving two distinct low pressures unfolds.

LWX CWA weather advisories updated 11:21PM EDT March 19, 2018.

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The winter storm watch is for accumulations of 5 or more inches of wet snow.

Here is the main CWG write up (updated through 10:35PM) (link embedded): Winter storm to bring wintry mix to D.C. area Tuesday and Wednesday with accumulation possible.

GFS 0Z 3/20/2018 showing 6-hr precipitation and MSLP for the NECONUS, valid hour 18 at 18Z March 20, 2018 as prettied up by Tropical Tidbits.

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The lead paragraph of Sterling (LWX) area forecast discussion from 8:18PM tonight sums it up as follows:

Low pressure over southern Missouri will push across the Tennessee Valley later tonight. A coastal low will develop along the mid-Atlantic Coast Tuesday ahead of this main low pressure system. A second low pressure system will develop off of the Tidewater of Virginia Tuesday night and move northeast Wednesday. Canadian high pressure returns for the latter half of the work week.

GFS 0Z 3/20/2018 showing 6-hr precipitation and MSLP for the NECONUS, valid hour 42 at 18Z March 21, 2018 as prettied up by Tropical Tidbits.

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Well, I was going to put more of the discussion and interspersed with forecast model images from the NAM, operational GFS, and operational Euro including snow totals. However, after perusing the Storm Hamster site written by Cranky Weather Guy in his characteristically overwhelming, insightful, but borderline vituperative tone, I'm now not inclined to do it.

This isn't going to be "Snowquester" bullshit all over again as far as I'm concerned in terms of falling for something that is patently absurd.

North America satellite picture with explanation of features, March 19, 2018.

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Suffice it to say, I perused his most recent write up and he is bearish on snow prospects given how late in the season it is and how little genuinely cold air is in place. He gives the D.C. area just 1 to 3 inches but on the doorstep of 3 to 6 inches.

Cranky Weather Guy's snowfall map forecast for the period March 20 - 22, March 2018.

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About those snowfall forecast maps, to be clear, the models do not generate those. Instead, they are created by other outfits such as Tropical Tidbits, Weather.us, Pivotal Weather, and WeatherBELL Analytics that get the data including temperature profiles and boundary layer conditions plus a specified snowfall-to-liquid ratio (i.e., the 10:1 ratio) which for this system is simply unrealistic given the time of year.

6Z 3/19/2018 NAM snowfall total map created by Tropical Tidbits with CrankyWxGuy's take on the matter.

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Below are some of the aforementioned snowfall outputs along with CrankyWxGuy's take on the matter on why those totals should be ignored this time of year and for this event.

European 12Z 3/19/2018 snowfall map for the mid-Atlantic valid 9AM EDT March 22, 2018 as created by Weather.us.

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From Cranky Weather Guy:

Observations made here's your problem. This is utter trash to be ignored. There is sleet which is converted to snow by the model and that's how you get these insane totals. Up north you halve the totals because it's not 25 degrees and at night. Hey, when it's VERY cold out? You trust these things. When it's 35 degrees and daytime in late March? You cut back.

GFS 18Z 3/19/2018 snowfall map for the NECONUS valid hour 60 at 6Z March 22, 2018 from Tropical Tidbits.

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Yet everyone sees the pretty colors, sees it doesn't match the forecasts, and starts gunning for heads. All I can do is show you the error. This is a lot of mixed precipitation and sleet. It is not pure snow. These maps are 10:1 ratio but our system won't do that...it'll be lower. 6:1 to 8:1 for most. There is just so much wrong with these maps outside of any very cold environment. At best, use the outlines to say "ok the model wants frozen precip in this zone" yet ignore the totals. It'll drive you crazy.

GFS 0Z 3/20/2018 snowfall map for the NECONUS valid hour 54 at 6Z March 22, 2018 from Tropical Tidbits.

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I know you don't care. The colors are pretty, and screw this guy for not forecasting one to two feet of snow. You mean like the last storm when the NAM had one to two feet for the Mid-Atlantic and you got NOTHING? Oh, that, right. Meh....enough with these stupid maps.

NAM 18Z 3/19/2018 snowfall map for the NECONUS valid hour 60 at 6Z March 22, 2018 from Tropical Tidbits.

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Use your tools, know the layers, figure it out without them. OR don't. Enjoy the dumpster fire and the arguing. I am thankful many have gotten the message to leave me out of it, and have, and I ask to please continue to do so. I just don't operate in the manner of "did you see the NAM why aren't you forecasting five feet." I'm showing you why. Agree, disagree, fine.

NAM 0Z 3/20/2018 snowfall map for the NECONUS valid hour 54 at 6Z March 22, 2018 from Tropical Tidbits.

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However, CrankyWxGuy notes how energetic this system will be -- with convection and the possibility of thundersleet.

College of DuPage NEXLAB simulated radar image valid 11Z March 21, 2018.

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I'd like to conclude with a few points:

First, the deterministic European (ECMWF) model has been insistent on a moderate-to-heavy wet snow for this part of the mid-Atlantic including the Baltimore/Washington corridor for days (through multiple runs), and now the GFS and NAM are on board even if details and amounts differ.

Secondly, even taking into account the very late time of the year for snow (season / sun angle) and our area's propensity for would-be snowstorm busts, it is not a good idea to discount the European model when it is being so insistent for a potentially high-impact event in a densely populated area.

This would explain the hoisting by the NWS of a winter storm watch for the entire region.

Having said that, though, Cranky Weather Guy sees this as an underwhelming event all around in terms of snowfall total, and he's usually correct.

UPDATED before posting

Even CrankyWeatherGuy updated his totals but he did it on his Twitter page instead of his Storm Hamster sit:

Cranky Weather Guy's updated snowfall map forecast for March 20 - 22, March 2018.

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OK, that's all for now. I would like to post a political themed entry at some point. Right now, though, it's late and I'm home -- after work and a gym visit -- and watching the late night MeTV line up and I'd like to get to sleep soon. I'm well into Cannon at this point -- which is way, way too late.

Tomorrow is a non-gym night but I also have an editing assignment to finish. Weather depending, my next update won't be until Wednesday.

OK, that's all for now.

--Regulus

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