With the peak of the snowstorm within 24 hours, I wanted to publish another free update to our forecast. Little has changed, however. I have a very detailed update available on our Premium subscription site, and for $1.99 you can purchase the individual forecast, along with the school cancellation forecast, here. Here, I want to again lay out some accumulation and timing details as they have come in, just updating some small parts of the forecast. So I’ll dive right in:
Precipitation Accumulation: 6-10 inches inland (isolated to 12 inches north of I-84), 4-8 inches inland of coastal towns, 3-6 inches south of I-95, 2-4 inches immediate coast/beaches
First, the forecast for Winter Storm Watches down to the coast was realized, as the National Weather Service did expand them down to the coast. They have not been upgraded to Warnings like inland areas have as confidence is not yet there on exactly where the rain/snow line will be, which is exactly what we are seeing now with the overnight model shifts. However, inland Winter Storm Warnings are up, and this is most certainly the correct call. The forecast remains for any inland towns (at least 5 miles north of the Merritt Parkway/Hutch) 6-10 inches of a slushy snow. North of I-84 there remains potential, in the most extreme banding, for up to a foot of snow, though this does not look particularly likely. Though the range is 6-10 inches, it is likely that the regions closest to the Merritt/Hutch will see somewhere in the 6 inch range, and the 10-inch range now looks to be most widespread up by the I-84 corridor. Up there we continue to have confidence that, even with a brief start as rain, they will turn to all snow quickly. Inland parts of coastal towns (primarily around the Hutch/Merritt) we are continuing to look for 4-8 inches of snow. It looks like 4 or 5 inch amounts will dominate more than 7 or 8 inch amounts, with amounts up to 7 or 8 inches really only possible across the furthest inland parts of these towns. And then south of Interstate 95 I continue to only expect 3-6 inches of snow, with again only 2-4 inches of snow at the immediate coast. What this means is that we could be dealing with a storm where the immediate coast sees 2 inches and someone inland sees 12 inches. That just seems to put in perspective what a difficult forecast this is, and what an influence the coast can have on these really close calls.
The going forecast, as you can see, remains from yesterday, but I still do have a couple minor concerns, including this one I outlined in the premium post: The only serious concern I continue to hold is the warmer surface temperatures that many of the models show for the immediate coast. Some show that south of I-95 surface temperatures will not get below 35 degrees. Should this be the case, it may be hard to get significant accumulations, with some snow actually melting and compacting while already on the ground. This will lower accumulation amounts when measured after the storm. I’ve had this concern since the beginning of the storm (after all, this is what leads to the really low snow ratios that I had previously talked about), but it is even more pronounced for the immediate coast than it was earlier. This is one of those scenarios where a couple degree difference can make all the difference, and thus it is hard to adjust a forecast on something like this when you still can’t really be sure exactly what the trend is. We need the very short-range models (HRRR, RAP) to get into proper range to see exact temperature profiles with this will be, but I am concerned about the immediate coast much more than anyone else. Inland towns I remain highly confident will see at least 6 inches of snow, and I agree with the Winter Storm Warning in effect there. Over the next few hours we will see if the National Weather Service puts coastal towns in a Winter Storm Warning or a Winter Weather Advisory…either way, it should specify that the immediate coast will see fewer accumulations than further inland, very similar to the October 2011 storm.
What this all means for the forecast, however, is that the coastal forecast is highly volatile. If snow sticks and it is just cold enough, we could certainly see up to 4 inches even at the immediate coast. However, if temperatures stay in the mid 30s and snow remains mixed enough with rain, it will be exceedingly difficult to see accumulations, except for maybe on grassy surfaces. This is mainly a problem south of Interstate 95, as north of there I believe surface temperatures will be cold enough for accumulating snow to get within the range I expected. Still, what we see setting up is a very extreme gradient setting up, and this can make for an exceedingly difficult forecast.
TIMING: So with timing, the forecast still remains generally the same. Precipitation starts between 4 and 6 AM as all rain, turning by around 7 AM to snow further inland. By 9 AM, everywhere except for maybe the immediate coast will be snow, and by 10 AM the entire region should be seeing snow stick on grassy surface except, again, maybe the immediate coast. Heavy snow continues through 1 PM, at which point even the coast should be seeing frozen precipitation sticking. Around 12 or 1 PM is when there is a chance that sleet could mix in, especially across southern New Haven county. It is in this time frame frame 12 PM to 4 PM that we will see some of the heaviest precipitation but also that there could be a brief warm layer, thus limiting coastal accumulations. Even if there is not sleet, the boundary layer will still be so marginal that any snowfall at the coast will be very wet, heavy, and low ratio. By around 5 PM any sleet across the region begins to wind down, and then snow will end from west to east between 6 and 10 PM. The cleanup will start, then, overnight tomorrow night to get roads ready for Thanksgiving.
That is what we continue to expect across the entire region at this time. Again, for more detailed school forecast and expected travel impacts, please do check out the premium post. I will say that we do expect widespread school impacts tomorrow, however the school impact forecast is very location-dependent, which is why I had to explain it so much. I will be sure to post another free update this evening as well, so make sure to stay tuned! The sidebar on the right will also be updated through the storm, and we will continue to have constant Twitter updates.