Wednesday, 12 Dec 2018

Washington is still riding on a possible snowstorm Sunday to Monday

Eric Tomlinson Jax's burrow mix is ​​sitting on the sidewalk during the first snow of the season in Washington on November 15th. (Calla Kessler / The Washington Post) A threat of unclear snow persists Sunday in the Washington area. We would like to be able to provide new details as to whether we are facing a significant snow episode, but computer models still diverge. The area may receive no snow, some snow, moderate snow or even heavy snow. The models vary depending on the timing of the storm, but if the snow materializes, it should start between Sunday morning and evening (the afternoon seems most likely) and probably end around Monday. the first hours of the morning are most likely, but some models suggest that the storm could extend in the evening.

(Washington Post) Here is how we would spread our chances of accumulation for the moment: Risk of not snow: 35% Risk of at least one dusting: 65% Risk of at least one inch: 35% Risk of at least three inches: 25 Risk of at least six inches: 15% The chances of snow increase when you head south and southwest of Washington and decrease to the north. The southwestern part of Virginia, including Roanoke and Blacksburg, is still expected to face a major snowstorm. Readers might wonder why the forecasts in Washington are so ambiguous. There are several reasons: 1) This prediction is very dependent on the complex interaction between the north and south branches of the jet-stream, whose models often have difficulty in standing. One of the keys to this forecast is whether the north flow relaxes enough to allow the storm along the south flow to head north. 2) The exact location of the storm is of paramount importance to our snow prospects, but it's a great map. On Monday evening, the 51 simulations performed in the European modeling system show a huge dispersion of the storm and its low pressure center. Those with the center on the coast offer abundant snow. But those more to the east would produce a dusting of an inch at most. The spread in these forecasts strongly advocates the maintenance of all options, from a major snowstorm to a complete failure.

European modeling system simulating the position of storm or low pressure centers, indicated by a red L, on Monday. ( 3) The beginning of the event being postponed perhaps to Sunday afternoon or at night, we are still in the window of time where the forecast predictability is low. The uncertainty of the forecasts is reflected in the following model solutions: US Operational Model (GFS): The snowwall is just approaching Washington, offering dusting around the city and keeping it dry to the north.

US model simulation (GFS) of snow Sunday night – mainly south of Washington. American Experimental Model (GFS-FV3): It projects several inches of snow from the South Beltway but decreases to the north and little or no snow in northern Maryland. The snow starts late Sunday morning or early afternoon and continues all night. Note that the forecast of snowfall has
drastically dropped (15 to 20 inches to 3 to 6 inches) over the past 24 hours, when he predicted heavy snow.
Simulation of an experimental American model (GFS-FV3) of snow in the D.C. region Sunday evening. ( Canadian model: As he moved away from a big storm in our region in his forecast released on Tuesday, he predicts again a heavy snow, perhaps mixed with sleet or rain. The snow would start Sunday morning and last all night. The massive change between these two forecasts illustrates how difficult this model is for models.

A Canadian model shows heavy snow in the Washington area Sunday night. European model: It barely brings the northern edge of the snow in the Washington area with little or no accumulation. The US modeling system, which contains 20 simulations in addition to the main operational forecast presented above, shows a wide range of forecasts. It is roughly evenly divided between snowless, somewhat snowy, moderate and strong forecasts. On average, it predicts a little less snow than Tuesday at the same time.

Snow simulations of the US modeling system for Sunday and Monday storms. ( So what do we know? A storm will cross the southeast coast until the end of the weekend. The storm will be wet across the south and will likely produce heavy snow in the mountains from western North Carolina to southwestern Virginia. The big question is how far north the thick snow line is going. We will continue to follow the storm over the next few days and provide updates.

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