A Premium update was recently passed onto clients updating the snowfall forecast and detailing various aspects of the going forecast. Portions of it have been freely released to keep you informed about upcoming dangers with the storm:
Westchester County is now forecast to receive 10-20 inches of snow, down from the previously forecast 16-28 inch range. Though a seemingly large shift, the forecast had always been for Westchester to receive around 16 inches of snow, and to emphasize this and to go off recent model trends and surface observations, I found it prudent to lower their accumulations. I see Westchester likely in the middle of that range, possibly seeing something like 12-16 inches of snow, but the high-end possibility is that some areas see up to 20 inches, and the low-end scenario is that the storm shifts far enough east that some areas in Westchester only get to around 10 inches of snow. In extreme northwestern Westchester by the Hudson river, amounts lower than 10 inches are actually possible as well. I was tempted to slightly lower the Fairfield County forecast as well, but am holding firm there as I like the overall forecast I set out with at first, and this update is only to emphasize the very sharp gradient that I see potentially cutting out western parts of Westchester County.
What to watch for is when that steadier banding on radar here moves into the region. The RAP has precip kind of bounce around in intensity until we get the steadier, heavier banding begin to move in around midnight to 1 AM. Looking at the radar, this looks fairly reasonable. The heavier banding on radar actually looks a little west of where the RAP wants to set it all up. Again, a signal that the RAP should continue to correct slightly west which it has done run after run and keep the forecast that I have out high confidence. So, watch for that heavy banding to move into the region first around 11 PM in New Haven, 12 AM in Fairfield County, and 1 AM into Westchester. Radar shows the first extreme band setting up over ester Long Island, and running a simple time line gives an estimate that it could be here as soon as 10 PM, maybe a little earlier than the RAP shows. But there is definitely intensification of this precipitation shield and intensification of the banding out to the east. To the west there is still drier air trying to win out as Westchester County sees very little snow currently, and that is one of the reasons why I am so concerned about their totals and have lowered them. But New Haven County is already starting to see that heavier banding, and eastern Fairfield County should be in it fairly soon too. As the RAP shows, by 2 AM here that is entering into Westchester County, as the model prints out the wettest run yet.
Overall, many signs are pointing to this forecast remaining on track despite the HRRR weather model showing a potentially major bust. I would take the RAP weather model over the HRRR easily, and surface observations continue to indicate that small trends west and wetter with the RAP should compensate for the underperformance the model is currently predicting. The next free update will come around 10:30 or 11 PM and will further these trends and tweak the forecast if necessary, but I really do like where I stand right now. Still going for 16-28 inches in Fairfield and New Haven, again with the higher amounts in New Haven, and now 10-20 inches across Westchester County. It’s mainly northwestern Westchester County that I am more convinced is unlikely to hit 16 inches, which got me to lower it, as eastern Westchester County should easily break 12 inches and possibly come close to testing 20 in a more favorable setup.
It’ll be awhile before the short-range models show the demise of the storm, and it will be interesting to see where they set up the continued banding as the storm weakens and pulls away, as that is where the heaviest accumulations could be as well. Where the bands set up could see continued moderate snow as late as 4 or 5 PM tomorrow before snow winds down by around 7 PM at the latest (probably earlier), whereas areas that don’t see continued banding could see snow lightening up as early as 1 or 2 PM. Just yet another piece of the puzzle to watch closely with this storm. As I said, I’ll have another free update around 10:30/11PM. Stay tuned for the latest!