Monday Evening Update:
18z Numerical Model Guidance run this afternoon would seem to favor a slightly colder scenario for the DC metropolitan region. Previous runs turned precipitation over to plain rain Wednesday afternoon as a warm nose of surface air shot northeastward. However, the 18z GFS run was slightly colder around the region for the duration of this storm, certainly a good sign for winter-weather lovers.

Still, for those of you who enjoy snow, you're probably going to have to wait for the next storm (if there is one). The snow currently falling across the area is associated with an upper level disturbance out ahead of the main weather system currently sitting in northern Texas .

Very little in the way of accumulation is expected tonight in the immediate metro area. Temperatures will slowly fall into the upper 20s and lower 30s.

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Potential For Significant Snowstorm in Mid Atlantic:
After a brief hiccup in the numerical modeling of this latest winter storm (OOz run of the Global Forecast System painted and absolutely horrific snowfall forecast for the region), guidance seems to be on track once again. The Latest GFS run pumps out close to 1.25 inches of liquid precipitation, which, under the standard 10:1 snow to rain ratio, would yield a 12 inch snowfall for the region.

While there are still significant differences in the vertical temperature profile of the atmosphere during this event, I have enough confidence to outline potentials with this potential storm.

1. I am confident that light to moderate snow will break out across the region from west to east sometime late Monday night or early Tuesday morning. This precipitation will be associated with warm air in the upper levels sliding over a dense dome of cold air near the surface.
   
2. The second part of the storm, likely the most significant sow-maker for us, should arrive sometime Tuesday night into Wednesday morning.
   
3. All Precipitation should exit the region by Wednesday night

Precipitation-Type Issues:
From a climatological standpoint, major winter storms rarely finish without some kind of precipitation change-over, either from snow to freezing rain, or from snow to sleet, at least in the Mid Atlantic. The North American Mesoscale Model (NAM), which honestly does not perform that well at 84 hours, is indicating the potential for a change-over from snow to sleet early Wednesday morning as low pressure systems get cranking to our south.

The GFS is much colder, on the other hand, and keeps all of the precipitation in the form of snow from DC north and west. Areas closer to the Bay in Southeastern Maryland will likely change over to a mixture of rain/snow/and sleet on Wednesday.

If the snow does in fact change over to sleet and/or freezing rain, snow totals would be significantly lower than if we managed to remain all snow. At this point, I think the majority of the storm will be snow, but I cannot rule out the possibility that areas as far north as Hagerstown change over to sleet at some point during the storm.

Even with the usual disparity among computer model guidance, there is a relatively high risk of a significant winter event in the Mid Atlantic early next week. I am very confident that a snowfall of at least 4 inches is in order for the Washington, D.C. metropolitan region.