Dangerous Travel Expected Tonight Into Sunday Morning

Premium subscribers have been receiving reports on the upcoming storm, but a freely released version of the forecast is also available below:

Snow has started on time slowly across the region but then picking up in intensity.  It will continue through approximately 10 or 11 PM, at which point coastal areas will start mixing with freezing rain.  Between 10 PM and 12 AM the coastal plain turns from snow to freezing rain and then to plain rain, while inland areas begin turning to freezing rain around 12 AM and could take until 1 AM or even a little later to turn over to plain rain.  Plain rain then continues through between 3 and 6 AM before moving out of the region, with clearing during the day on Sunday.  Thus, this timing looks to spare the region some of the worst impacts by having the most dangerous travel late Saturday night, where roads could easily be avoidable with proper planning.  There is fairly strong agreement among the weather models as well that we start all snow before gradually turning to freezing rain at the coast, rapidly spreading inland and then going over to all rain for a few hours before winding down.

As for accumulations, the National Weather Service has issued Winter Weather Advisories calling for 2-5 inches of snow across the region, right in line with what I was expecting.  However, I am becoming skeptical that the changeover hits inland areas before 10 PM, and thus was considering upping inland accumulations.  I believe that coastal areas still see 2-5 inches of snow (likely much closer to the 5 inch range, but a quicker turnover could melt some down to make it closer 2 inches) while inland areas I have decided to also keep in the 2-5 inch range.  I think only an extra half hour or hour of moderate precipitation falling as snow inland will not be enough to boost accumulations by more than  an inch more than the coast, and thus will keep them in the same range, especially as some models show slightly more liquid at the coast than inland.  As for ice, there is fairly strong model agreement in at least an hour or two of icing across the region which has me concerned.  Especially with the strong snow pack keeping the surface cold, at least some ice accumulations appear likely.  I generally expect .05-.15 inches of ice across the region.  I’d be surprised to see more than .15 inches of ice as the surface does warm fairly quickly once upper levels of the atmosphere warms, but I do expect to see at least ice from this system.  Then, after all this, we will likely see around a quarter to a third of an inch of plain rain falling into the snowpack.

The main concern I have is for road impacts between 5 PM and midnight.  That is when roads look to generally be in the worst shape across the region.  Extremely low temperatures tonight could keep surface temperatures below freezing slightly longer than air temperatures, meaning that ice could also last a little longer than some are expecting. This means in coastal areas, I’m expecting worst road conditions in the 8 PM to 11 PM timeframe with roads improving through the night as we turn over to plain rain, and inland I expect worst road conditions from 8 PM until 1 AM.

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