WASHINGTON - We have gone through another 24-hours of weather model data and while the big picture does remain generally the same, there have been some notable differences and trends in the weather modeling over the last day.
One thing that has not changed much at all is the timing of this system. Most guidance agrees that after a dry but extremely cold morning and afternoon on Saturday, snowfall will begin to approach the region on Saturday night.
European Weather Model Forecast For 10 p.m. Saturday Night
The timing:
At this time, it looks like the first flakes could possible fall in the 8 p.m. to 12 a.m. window, though one thing we will need to monitor is the cold air in place Saturday afternoon. It may take a couple of hours of snow falling and evaporating atmospherically before it begins to reach the surface in the D.C. region. This is because cold air is extremely dry, and it takes time to moisten up the air mass enough to the point that snow can fall.
European Model Forecast for 7 a.m. Sunday Morning
Once the snow does start to fall, it is likely to rapidly increase in intensity into the overnight hours. Snowfall rates could easily eclipse 1-2" per hour rates, with every flake sticking given the strength of the cold temperatures in the region throughout the day on Saturday. We will not be losing any to ground melt this time around. The early morning hours of Sunday look like when the most widespread, heavy snowfall will be in the D.C. region.
European Model Forecast for 2 p.m. Sunday Afternoon
The big question this afternoon is, will this be an all-snow event, or will some milder temperatures sneak into the middle levels of the atmosphere and change parts of the region over to sleet or even freezing rain on Sunday afternoon. This may surprise some as temperatures for the vast majority of the region will remain well below freezing throughout the event. It is not always what is going on at the surface that matters though.
Temperatures 4000-5000 feet above the surface, with yellow and reds indicating where temperatures are above freezing.
Meteorologists call it a "warm-nose", a zone of warmer temperatures in the middle levels of the atmosphere that can melt snowfall before it hits the ground, so it ends up falling as freezing rain or sleet depending on temperatures at the surface. At present time, the American model (GFS) suggests that this will not be an issue for the region, and the storm will remain an entirely snow event for much of the DC region. The European model however (shown above), generally considered to be a more accurate model, does suggest that after morning snowfall, this zone of milder temperatures will advance up the I-95 corridor and areas to the east. This would change snow over to sleet and freezing rain, and limit additional snow accumulations in these regions after Sunday morning. This is a feature the weather team will be tracking heavily in the coming days that could lead to farther forecast adjustments.
European Model Forecast for Sunday at 11:30 p.m.
The storm then exits sometime between late Sunday night and early Monday morning across the DC region. It its wake, temperatures plummet, with most dropping into the teens Monday morning. Anything liquid will freeze, and with temperatures that low, road chemicals will not work nearly as well as they would when temperatures are closer to the freezing mark. Travel conditions are likely to remain dangerous due to icing issues for a couple days after this storm exits. This will be a major impact storm that has lasting effects well into next week.
American Model snowfall output For D.C. area from Wednesday evening
The amounts:
So how has this impacted what we are expecting in the DC region. Weather models remain high with their numbers. The American model, which never transitioned the DC area over to any sleet and left the storm as snow, has a widespread 10-17" of snow across the DC region. Our opinion is that these numbers are likely a bit on the high side, as we do expect the DC area will likely see mix work its way up at some point on Sunday. Especially in our southeastern zones.
The European Model snowfall forecast from Wednesday night
The European model on the other hand, which shows the mixing coming in, has a much more "typical" look of a Mid-Atlantic snowstorm. Lower amounts southeast, with higher amounts northwest. The numbers no doubt are jumping out at you in these zones. Two feet of snow?! Not out of the realm of possibility, though in many of these locations we would probably lean a bit closer to 12-18", with DC proper more in the 8-14" range with the mixing threat. We have not put out our official snowfall forecast from Fox 5 just yet as we continue to examine the data that is coming in, so we can present you with the forecast we feel is the most likely and most accurate.
A key difference in the American model and the European model is how moisture heavy they are. The entire reason that the model shows mixing at all is it shows more direct southwest flow off the Gulf. This naturally brings up some milder air, but also brings up a whole lot more moisture with it. More moisture means heavier snowfall potential, and that is why it has significantly higher totals northwest when compared to the American model. The tradeoff for these higher totals, is that at some point you are likely to mix. As the farther that mixing line advances northwest, the more you will see those higher numbers push northwest. Simple as that!
D.C. has only had two snowstorms in the last decade that brought over 10" of snow to DCA
What else can change?:
As you might expect from the discussion above, the key that we will be watching over the next couple of days here is how modeling handles that snow-mix line on Sunday afternoon. The timing of it, and how far it advances northwest, will impact snowfall totals. I do want to mention though that there is still excellent agreement that everyone gets a solid snowfall on the front half of this winter storm event, it is what happens during the latter part of it that is in question and could impact the finals totals. I know every snow lover in our region wants to see 20"+ at their house, but that is hard to do.
DC has only seen a single event in the last 10 years that got close to the number that the European model is currently showing in Washington, and that was the Blizzard of January 2016. While this is likely to be one of our better snow events of the last decade, dynamically it is not the Blizzard of 2016, so I really do feel we will struggle to close to see DCA get close to that 17.8" that we got back then. We are working on our snowfall map and hope to put out some of our numbers tomorrow. At the moment I’m leaning towards 8-14" around DC, 5-10" southeast, and more like 12-18"+ northwest but these are VERY preliminary numbers.
We have another round of guidance rolling in overnight that should provide us a clearer picture. NOAA and the National Weather Service are so concerned about the widespread impacts of this system that they are flying Hurricane Hunter missions into the storm energy so that it can be better sampled for future weather model runs. So future cycles should provide a much clearer picture. We will continue to keep you updated as the weekend storm approaches!