A Premium Update on shifting weather model guidance has been released and has updated the forecast snowfall accumulations across SWCT/NY. The updated snowfall forecast is outlined below.
FORECAST ACCUMULATIONS: Northern half of New Haven County: 4-8 inches. Coastal portions of New Haven County and far inland portions of Fairfield County see 6-12 inches of snow, again increasing in amount as we get close to the coast. Inland Westchester and coastal Fairfield Counties see 8-16 inches of snow, while southern Westchester may see 10-18+ inches.
First, the latest HRRR shows now that by 11 AM tomorrow Westchester has 4-5 inches of snow on the ground with 3-4 inches in Fairfield County and 1-2 in New Haven, seen here. This is before the bulk of the heaviest snow moves in, which means that Westchester is increasingly likely to see over a foot of snow. The 0z HD NAM shows up to 20 inches in Westchester with an insane gradient causing only around 10-11 inches in New Haven, seen here. The RAP has been consistent showing around 12-16 inches at the immediate coast, and the consensus continues to be that between Westchester and New Haven Counties is where the gradient sets up.
I do think the SREFs are a little overdone in showing 15-18 inches as the mean at the coast, seen here. Some of them also have some sleet mixing in, which the NAM has shown. Still, having a mean of all the SREF members show such a strong gradient is really striking, and hopefully demonstrates how low confidence this forecast is overall. Taking all this into account, I have decided to once again slightly up the snowfall amounts. I have also gotten even more specific with the ranges, as the difference between inland New Haven and coastal Westchester is likely to be dramatic if the storm plays out anything like what most models show.
It is somewhat of a cop out to have such large ranges (I typically hate a range of 8-16 inches as an 8 inch snow storm is significantly different than a 16 inch snow storm) but even when breaking down the counties like this we could easily see 8 inches and 16 inches within a few miles of each other depending on where the strongest banding stalls. We can see that on the HD NAM forecast snowfall here. The model shows the potential for Greenwich to see 18 inches of snow and Milford sees 10-12 inches. This is a significant difference over a very small area, and such a gradient definitely appears likely to set up. This will keep the forecast extremely volatile, with tine shifts overnight making huge differences during the day tomorrow.
Finally, models have extended the end of the storm all the way back towards sometime between 9 PM Saturday and 2 AM Sunday. It is looking like it will stick around a little bit longer, and that has increased confidence that widespread amounts of 8-10 inches are essentially a given and widespread amounts of over a foot at the coast are possible.