The below update comes from a recent Premium update emailed out to subscribers. This details the latest forecast for the upcoming sleet/ice event overnight, explaining the latest accumulation forecasts, timing expectations, and potential travel impacts. To see expectations for school/business delays and impacts tomorrow and to begin receiving more detailed email updates ahead of winter weather events, subscribe here.
Generally, the forecast has remained unchanged. We see some sleet showers beginning to approach the region off to the west, and in the next few hours we may see the first light sleet across the region. However, any steady, accumulating precipitation still looks to hold off until at least midnight. Some scattered icy conditions could occur in any light sleet shower but nothing to seriously worry about, as travel waits to go downhill until around midnight at the earliest. Sleet still looks to become steady around 2 AM in line with most expectations, and from there through 5 AM the entire region should be seeing steady sleet showers. In between sleet, when precipitation lightens up to maybe even a drizzle, we will have precipitation that will struggle to form large droplets, and instead we may see freezing drizzle, especially inland. This is my largest concern for icy roads overnight, and why the morning commute inland could still be an issue.
By 5 AM, anywhere south of Route 15 should be rising above freezing, and any sleet should go over to plain rain by around 6 AM. Travel conditions should improve from there; at no point should coastal travel really be that much of an issue. Midnight through 6 AM is the only time there could be some slippery patches as temperatures dip below freezing, but that is about it. Moderate to maybe even briefly heavy rain through Tuesday morning will continue along the coast before we dry out gradually through the afternoon.
Meanwhile, it is further inland that there remain some questions. Most weather guidance designed for the medium and long-range shows that temperatures across all of Fairfield, New Haven, and Westchester counties will be above freezing by 7 AM. This means that road conditions would be improving in those regions by 7 to 8 AM at the latest. Similarly, guidance is indicating that there is unlikely to be that long a period of freezing rain along the I-84 corridor, instead favoring primarily sleet. This would mean that sleet accumulations would be slightly higher (maybe a little over an inch inland) and that ice accretions would be slightly less. Still, I am not totally buying some of this short-range output after such consistent freezing rain signals on soundings, and for now am continuing to forecast just up to 1 inch of sleet even in northern portions of the three counties. Sleet accumulations should wind down by 5 or 6 AM, though we may alternate in some regions between freezing rain and sleet after 3 AM depending on the intensify of precipitation.
Short-range HRRR guidance shows that freezing pockets could remain isolated inland through around 8 or 9 AM. This would make travel dangerous through around 9 or 10 AM, versus the 8 AM timeframe that most other weather models had been showing. Essentially, anywhere more than 5-10 miles south of Interstate 84 should see travel conditions improving by 7 AM, and coastal regions may not even have travel problems in the first place. Even inland regions will see warming temperatures overnight unless the overly cold HRRR guidance verifies (I struggle to trust this guidance outside of 10 hours, as it will likely trend slightly warmer in future runs to fit the forecast that I have outlined up above). Then, far inland I believe travel does not significantly improve until closer to 8 AM and maybe even 9 AM in a few isolated areas. It is further inland, in northern Connecticut into Massachusetts, that colder weather should linger enough for serious travel issues, business closures, etc. but impacts across the SWCT/NY region appear relatively limited at this time.
Overall, accumulations of up to an inch or two of sleet inland still appear possible, and up to a tenth of an inch of ice inland is also looking possible (though slightly less precipitation as freezing rain should keep accumulations from being more than a tenth of an inch, especially with relatively marginal surface temperatures). The only low-confidence part of this forecast is the rate of warming across the region, with quicker warming allowing travel conditions to improve even by I-84 as early as 7/7:30 AM, with the cold lingering slightly longer possibly keeping us icy through 8 or 9 AM. Coastal areas have little to worry about, as even in the coldest scenarios temperatures are above freezing by 6 or 7 AM, and sleet may melt on most surfaces as it falls there regardless, ensuring any accumulations are minimal.