SPRING SNOW THREAT: Winter storm warnings issued for DC region

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Even while spring officially begins just after noon on Tuesday, the National Weather Service says there is a possibility of 5 inches or more of snow for the area.

Just before 1 pm Tuesday, a Winter Storm Warning was issued for the D.C. region, including much of Maryland, Northern Virginia, and the District of Columbia, from late 2 a.m. Wednesday through 8 p.m. Wednesday.

While D.C., central Maryland and Virginia could see 2 to 6 inches, areas west of I-81 in Western Maryland and West Virginia could see over 6 inches. Cumberland, Maryland and Morgantown, West Virginia could see 8 inches or more.

Funny enough - last year's biggest snow of the season also came in March and the upcoming storm is expected to be similar in that it may be more of a "messy mix" than any single type of precipitation. To put it lightly, we have one of the trickiest forecasts in recent memory coming up over the next couple of days here in the D.C. region.

While the event itself will likely appear to be one prolonged event, it is actually two separate storms running consecutively to one another:

The first round of wintry precipitation Tuesday will bring slippery travel north and west of the District, where a Winter Weather Advisory is in effect for a snow and sleet mix.

The second round of wintry precipitation will come through late Tuesday night through Wednesday. It's expected to bring some accumulating snow to most of the area. It is under a Winter Watch for now.

While the forecast is likely to go through some adjustments over the next few days, here is our current thinking on what you can expect, depending on where you live, over the next 72 hours:

Monday Through Monday Evening

Region-Wide: No concerns about winter weather Monday. Some early sunshine will give way to more afternoon clouds ahead of the storm, but most of our area will remain dry through the evening hours. Spotty rain showers cannot be ruled out south or west of town, but this should be the exception rather than the rule.

Overnight Into Tuesday Morning

Northern Neck/Southern Maryland/Eastern Shore: Moisture overspreads the region from southwest to northeast. There is currently a good agreement between the weather models that we'll see surface temperatures above freezing and enough warm air aloft that the event should begin as mostly rain - although we can't rule out sleet mixing in in a few spots.

I-95 Corridor/D.C./Central MD/Northern VA: Current guidance suggests a rainy start in most of Northern Virginia and the immediate D.C. metro region. Higher elevated areas of Montgomery, Loudoun, and western Howard counties could see more sleet mixing in because these are areas that tend to just naturally run several degrees colder than the city. We do NOT anticipate any accumulations by sunrise in these locations. Wet roads will likely be the story of the morning commute - not snow covered roads.

I-81 Corridor/Western VA/WV Panhandle/Northern MD: While precipitation may initially begin as rain, sleet, or even freezing rain, our weather models try to transition over to snow pretty quickly across the highlands with enough cold air in place in the upper levels of the atmosphere. Although it is likely to initially melt on contact, it is also likely that some spots will see a steady enough snowfall to begin accumulating on grassy areas and possibly untreated roadways as well. These are the areas most likely to see morning commute impacts and possible school impacts as well.

Tuesday Afternoon - Early Evening

Northern Neck/Southern Maryland/Eastern Shore: Models still in good agreement of mostly rain. Some sleet may mix in from time to time, but at this time we are still not favoring major impact in these zones.

I-95 Corridor/D.C./Central MD/Northern VA: A classic storm in that the I-95 area will be the "battle zone" with this particular storm as it often is. Throughout the afternoon the rain/mix/snow line will likely dance back and forth across I-95 throughout the afternoon. A slushy, light accumulation of sleet is possible in counties just west of town by this time as this is where temperatures are more marginal. Impacts for the city itself will be entirely dependent on how much falls as rain and how much falls as sleet. It's a tricky call locally, but the fact this is still a mid-March event suggests the immediate area still is not looking too bad at this point. The evening commute will likely to be slower with the mixed precipitation across the region.

I-81 Corridor/Western VA/WV Panhandle/Northern MD: The areas most likely to see accumulating snow Tuesday afternoon. While most will likely be on the grass, the higher elevations may see surface temperatures remain below freezing and roads could become slick as well. Take it easy if you are traveling in these regions.

Tuesday After Sunset - Wednesday Morning

Northern Neck/Southern Maryland/Eastern Shore: The first storm begins to pack up and move out while the second storm gathers strength and pushes north to fill the void. As the storm develops and deepens off the coastline, colder air will begin to work its way in during the overnight hours. Slowly but steadily the rain/sleet/snow line should start to march its way eastward. Sleet could come down heavily from time to time, leading to some spotty slick spots, as well as a spotty accumulation of slushy sleet.

I-95 Corridor/D.C./Central MD/Northern VA: Transition should begin from sleet over to snow during the overnight hours. Temperatures will fall as the storm gathers strength and pulls in colder air. This is our best chance to accumulate several inches of snow locally. BUT it will all depend on how heavy the precipitation is. If snow falls too lightly, it will melt on contact. Heavier snow will lead to greater problems for the region.

I-81 Corridor/Western VA/WV Panhandle/Northern MD: Snow continues and, as temperatures drop after sunset, it should start to pile up in some spots. Highland roadways, as well as those that are untreated, may become slick and snow covered. Much like closer to town, the amount of snow that sticks will depend upon how heavy the snow is when it falls. Currently, most models have the "jackpot zone" of highest snowfall totals centered around the West Virginia panhandle.

The National

Wednesday Late Morning - Wednesday Afternoon

Northern Neck/Southern Maryland/Eastern Shore: Sleet may transition to snow, however, warm surface temperatures combined with a high afternoon March sun angle may limit accumulations and keep them confined to mostly grassy surfaces.

I-95 Corridor/D.C./Central MD/Northern VA: After sunshine, the accumulating snowfall should start to taper off as the storm system begins to pull away. Weather models are all very different on how fast this occurs, with several models showing the potential for higher snowfall totals while others show the potential for less. It is a very tricky forecast, but it is difficult to accumulate snow during the daylight hours during the second half of March. Snow should wrap up during the afternoon hours.

I-81 Corridor/Western VA/WV Panhandle/Northern MD: Snow becomes lighter and lighter as the storm pulls farther away from the coastline. While some additional light accumulations are possible but by this time this bulk of the storm should be over.

What Could Go Wrong?

This is a very complicated and tricky forecast. The irony that our biggest snow of the year could potentially come on the first day of spring is not lost. However, the reality is that we are still getting into late March, and accumulating snows are much more the exception than the rule this time of year. They are very hard to do. Temperatures above the surface - even a degree or two warmer or colder than model expectations - could lead to major forecast changes. The biggest concern around the immediate metro area is that it is more sleet and rain than actual snow even into Tuesday night, holding snowfall totals down. Northwest of town where the "jackpot zone" is currently sitting on our forecast map, but there is always the worry that dry air can intrude on the systems so far away from the storm center and then snowfall totals are once again cut down.

Higher amounts are not necessarily off the table locally either. New weather computer guidance in this morning did trend slightly colder than previous runs, which would run the transition of a faster transition to snow around the I-95. While this is currently not the favored scenario, it cannot be fully discounted either. We will need to observe new weather model data later on this afternoon to see whether or not this colder trend continues. Forecast adjustments will likely need to be made a little later on this afternoon.

In summary, this is a very low confidence forecast. We are so late in the snowfall season that getting a major winter storm with accumulating snowfall is extremely difficult. We will continue to bring you the latest information as it becomes available to us throughout the afternoon. Stay tuned!

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