Good evening everyone! Over the past week or so I have been tracking a winter storm threat for the DC area on Saturday. In the past 24 hours, models have consistently trended colder and more southeast, allowing for our region to garner higher snow accumulations. There is a winter weather advisory for I-95 corridor and north and west of that. 2-4" is expected in I-95 corridor, while 3-5" is expected NW of 95. The cold air will come in quickly and strong tomorrow. There will be a brief period of sleet while we transition over to snow tomorrow, which will help snow accumulate better. The freeze will also aid with this. The winds will be very strong tomorrow. Many areas will see wind gusts in excess of 50 MPH, up to 55 MPH. Due to winds and the heavy snow expected, blizzard conditions are possible tomorrow, particularly between 8 - 11 AM. In the WWA, it states the possibility for this. Thundersnow is also possible, mainly when we transition into snow(soundings support it). Winds are quite undermodeled. Tomorrow morning, we will have an FGEN band that will setup west of DC, but east of I81 as the transition to snow occurs. Rates could be 1-3" per hour in this band. Because of this, I really think west of DC should be placed under a winter storm warning. Just because it was 60 today does not mean snow will not accumulate. There have been many times where there were mild temps before onset of snow, and areas got a good amount of snow(1/3 as an example). I'll show some of the 18z mesoscale models here.
HRRR:
The HRRR has a very impressive snow accumulation, with the bulk of the snow falling in 6 hours. Latest runs of the HRRR are uptrending on snow accumulation too. I think this could be a legit overpreformer for our region, dynamics and FGEN banding are very impressive. The soundings from the HRRR scream FGEN band(winds rapidly veering with height, ample amount of omega and lift in DGZ) with good snow growth. I would cut totals by about 1/3 for a more realistic amount, but still a very impressive amount.
NAM 12KM:
NAM is quite impressive with snow accumulations, with a widespread swath of 6" and higher. Again I would cut totals by 1/3 - 1/2, but this was a big improvement from last run. The reason why is that NAM is slower, and colder and east, allowing for more snow accumulation. NAM 3KM supports this too.
NAM NEST(3KM):
The NAM 3KM is very impressive with dynamics + FGEN and supports the low-resolution NAM's solution. NAM 3KM is also impressive with a wide swath of 6"+. Again cut totals by 1/3-1/2. Much better than last run.
NAM 3KM has an impressive FGEN band moving through the region as rain turns into snow. A sounding reveals ptype being snow, with good dendritic growth. Winds rapidly veer, which indicates FGEN. There is good lift in the DGZ with nice omega values. This is a good sounding for heavy snow, and for strong dynamic cooling. This sounding also indicates some possible thundersnow in some areas.
My snow map:
Here is my final snowfall map. In the red, you can expect 4-8" of snow(Blue Ridge, Catoctin Mountains, Western MD). North of DC, you can expect 3-6" of snow. Most of the region DC and south are in the 1-3" range. Far southeastern parts of our region can expect C-1". I went a little bit bullish on the snow map because of latest trends on guidance leading to more snow. The dynamics and setup from this event is quite impressive. Even though rates are still uncertain, a FGEN band that will allow for these totals to come to fruition. The north winds will help blow snow and help transport cold air here. When rain transitions over to snow at around 5-8 am for most of the region, there will be a brief period of sleet. This will help snow accumulate, including the flash freeze. This will be a nice event for March. Whiteout conditions at times cannot be ruled out, and near blizzard conditions for somewhere are likely at one point at time. Even thundersnow is possible tomorrow(transition to rain - snow). This will probably be the last snow event looking at long range models, so enjoy everyone! Main roads should be fine but secondary roads will likely cave to the high snowfall rates.
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