While the Premium forecast discusses more specifically travel and school impacts for the storm tomorrow, going very in depth on a county-by-county basis of which counties should see the worst school and travel impacts, we did want to pass along a few forecast updates and analysis here. If you wish to purchase the Premium forecast, you can do so here. Simply click the subscribe button above should you wish to subscribe full-time to our Premium service:
The timing is the key aspect to figure out here. For example, the latest HRRR model shows this at 6 AM, which is a signal for freezing rain across all of the region. The problem is, the model does not show any precipitation accumulating. It tries to indicate that, instead, most of that precipitation does not reach the ground as the air is too dry to support precipitation at first, in what is called virga. This is fairly common. The latest RAP weather model shows something similar. This is what it suggest the radar will look like at 6 AM tomorrow. However, this is what it shows at the surface, with only far inland Westchester County seeing any accumulation through 6 AM. By 7 AM, you have this, which shows precipitation only inland. Still, precipitation is only a hundredth of an inch or so, though as freezing rain that is certainly enough to cause serious problems and likely worthy of closing schools. When the short-range guidance both shows virga and then does not have the steady precipitation move in until 8:30 or 9 AM, that is when I get concerned. It is likely that around 9 AM temperatures will still be below freezing across the area, so it is not a matter here of surface temperatures, but rather one of precipitation. Models now indicate that the region turns over to plain rain anywhere between 9 AM and 12 PM, with models seeming to indicate that Westchester County will actually remain the coldest for the duration of the storm based on the wind direction. This seems about right to me, though one degree different and the entire region could be freezing rain much longer than a lot of the weather models are predicting. Additionally, although the air temperature slowly rises above freezing, many regions are in the upper 20s right now and have been frozen for quite awhile, meaning that it will take even longer for them to rise above freezing. This is why I am still concerned about road conditions tomorrow morning, even if surface temperatures rise above freezing by 9 or 10 AM in some areas. New Haven County looks most likely to warm first, with Fairfield following and then Westchester County coming last. Again, just the timing and make-up of the storm that determine this. New Haven County could rise above freezing as early as 9 AM, whereas Fairfield County and Westchester County could see pockets of freezing rain into the early afternoon. RAP guidance indicates both of all counties does not rise above 34 or 35 degrees through 1 PM, meaning that it takes quite awhile for roads and other surfaces to rise above freezing.
The result of all of this is a very low-confidence forecast in impacts, as it is not possible at this time to determine exactly where will be rain and where will be freezing rain/ice between the hours of 10 AM and 3 PM tomorrow. Even after 3 PM, it appears a surface low pressure center will begin to take over to south and should flip winds from warming us up coming from the south to cooling us down coming from the north. If that low pressure center forms a little sooner, it could lock in the cold air, and some areas could see freezing rain or icy road conditions through the day tomorrow. There will be one more free update around 11:30 PM tonight, so please stay tuned.