Snow totals will vary as winter storm strikes region

1) Event Starts as SNOW tonight between 6 p.m. and 9p.m. Heavy snow starts during the late evening/overnight hours.

2) Winter Storm Warnings go into effect for Baltimore, D.C. and counties west of I-95 at 7 p.m. tonight. Winter Weather Advisories are up for some east of I-95.

3) Confidence is high on the highest snowfall totals north & west of town, with "jackpot" totals most likely in northern Maryland closer to the Mason-Dixon Line.

4) As you get closer to I-95 including D.C. and Baltimore the confidence in the snowfall forecast is MUCH lower. Snow mixing with sleet or rain can DRAMATICALLY reduce snowfall totals.

5) Main event wraps up Tuesday by mid-morning, but scattered snow showers continue through the day with a few locations possibly picking up another 1 inch late.

Let's start with what is already out there. The National Weather Service currently gives the District a 67 percent chance of receiving over 6 inches of snow before Tuesday is through. They were confident enough in the forecast that they issued Winter Storm Warnings on Sunday for D.C., Baltimore, and the vast majority of counties in our region that are west of Interstate 95. Snow looks to start sometime after the evening rush, but will really pick up in intensity after 10 p.m. tonight. Models have been pretty consistent with the storm starting as snow for everyone. As far as ground temperatures are concerned, subfreezing temperatures the past four nights have helped cool the ground significantly following the very warm start to the month, meaning snow should start sticking pretty quickly especially in areas north and west of town.

Time for some full disclosure through, I've got that sick feeling in my stomach with this snowstorm that in downtown Washington, Baltimore, eastern Montgomery, Fairfax, Arlington, and Fauquier could all under perform with this event. Why? Because of a rain/snow line that is nothing short of a forecaster's worst nightmare. While most will start as snow, as the storm center pushes up the coastline and intensifies, it will start to pull in some warmer Atlantic air and mix with sleet and rain. How far the rain/snow line dances westward will have major implications on our snow totals. Most overnight guidance was holding that rain/snow line just southeast of Washington, D.C. but some early morning guidance has been trying to track the storm a little closer to the coastline which would push that rain/snow line farther west across the District and perhaps into Fairfax and Montgomery counties.

The effects of the rain/snow line are huge. Looking at rainfall itself, models are generally putting between 0.8 and 1.6 inches of liquid across the D.C. region. If all of that fell as snow, it is easily a widespread 8 to 16 inches of snow for everyone! The problem is that will not be the case. Sleet does not pile up nearly as fast and has the added effect of compacting any snow that has already fallen. Prince Georges County, Calvert County, Charles County, St. Mary's County, Eastern Shore…this is NOT a big snow for you. At no time over the past several days did we think it would be a big snow for you. The big question zone is really along the Interstate 95 corridor itself. Do we mix? If we do, how long do me mix for? All of these will have major implications on snowfall totals. Models have been bouncing back and forth with where this line sets up all morning long. At this point you are a snow lover living in the District; it's a flip of the coin for a boom or a bust.

On the contrary, if you live north and west of town and are a snow lover, you should be feeling pretty good! Multiple model runs have been putting the jackpot zone from Interstate 270 to Interstate 70 corridor north to the Maryland boarder. Western Montgomery, western Howard, western Fauquier, and Loudoun counties should all take a good chunk out of their snowfall deficits as well. Of course many will be wondering about what schools will do. Our assumption is giving the timing of this system and the threat for heavy snow, we believe there will be widespread closings and delays. Regardless of what happens, we here at FOX 5 will be starting extra early at 4 a.m. tomorrow to keep you ahead of what the school systems and government decide to do, and will have live reports from those locations hit hardest by the storm.

Stay safe!

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