From the US National Weather Service
Starting to hear alot of chatter about snow this weekend? Lets break down the forecast and discuss some potential outcomes, and have a moment to talk about forecast uncertainty:
We like to think about the forecast as a train heading into the rail yard. You start on one track. As you go through time, that one track turns into two, then perhaps four, and eventually, you could end up with tens on potential tracks the train could take as it arrives. Lets think of these tracks as potential scenarios for the weather. You start off the forecast process right now on one track (there is really only one scenario for what’s happening right now). Out a couple days, there may be a couple scenarios for what weather might happen. If you go out as far as 5-7 days, the forecast has a good deal of uncertainty with many potential scenarios.
Ironically, much of the uncertainty in the weekend storm (most likely to happen between Saturday night and Monday) will come down to “tracks” (not the railroad ones). For simplicity, well break the storm potential down into three scenarios…
Scenario #1:
The storm track stays well to the south and the area ends up with very little to no snow. This would produce <1″ of snow accumulations, if any. This scenario is around 20% likely at this point given current weather prediction guidance. While mostly dry, scenario would be the coldest (temperatures 20-30F below average).
Scenario #2:
The storm track forms to the south and then curves north as it heads towards the mid-Atlantic region. In this scenario, the region would see snow, but not the worst of the storm. This storm track would produce notable accumulations (likely >1″ but <6″). This scenario is around 50% likely at this point given current weather prediction guidance.
Scenario #3:
The storm track forms to the south then curves up the spine of the Appalachians before reforming off the coast. In this scenario, the region would see the heaviest snow from the storm. This track would produce heavy accumulations (likely >6″ to as much as 12″). But this scenario is 30% at this time given current weather prediction guidance.
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