A recent Premium update sent out to subscribers detailed potential storm scenarios on our short-term weather models as the storm unfolds. Relevant portions have been freely attached below:
I think the HRRR model is out to lunch with this. It was good with the other storm, but so was the NAM. A short-term NAM/HRRR is hard to ignore, but here we see them at complete odds. At the same time, the NAM is likely entirely overdone. Looking at RAP guidance, you have this. A reasonable depiction through 7 AM showing about 10 inches having fallen region-wide with another 6-8 inches to go, except in New Haven where upwards of a foot may already be on the ground with maybe another foot to go. Recent surface observations show that the RAP has initialized fairly well, but the storm is slightly stronger and a little further northwest. You can see the current surface chart here. The low will rapidly strengthen as it moves to the north and gets captured by a 500mb upper level low. The question is how far west does that upper level low pull the surface low pressure, as that is where we will find the heaviest banding and snowfall. The NAM and ECMWF show a complete capture, pulling the storm west enough to create all out blizzard conditions in the SWCT/NY. Other guidance does not show enough of a capture for that, and thus some of these very high snow accumulation forecasts would bust. If the storm doesn’t capture the surface low properly, even my forecast would bust despite being on the lower end with a 16 inch minimum. If I see signs that the capture does not occur as planned, the immediate response would be to lower Westchester County to a 10-18 inch range, while maybe tweaking Fairfield County and holding with New Haven County. Right now, I do not see enough evidence to change the forecast, so I am holding firm with it. There is just a very high bust potential with the storm due to this tight gradient.
Observations thus far, however, seem to support some of the further west and strong forecasts, which is why the NWS is holding firm with their aggressive forecasts across the region. I don’t really blame them. It all just comes down to the next 6 hours 15,000 feet in the atmosphere, and how a low pressure center can cut off up there and influence the low pressure forming at the surface. Observations are going to be key to determining exactly where the worst conditions and impacts are to set up, and for many if and when they lose power. I still do not expect power outages to be widespread, and they may not even be scattered in some of the better scenarios, but it is not yet time to let down your guard in case that convective banding finds a way to set up over the region. Either way, some weather models are going to completely bust on their forecasts as they predict a sharp cutoff across a slightly different area. In the scheme of things, this is such a small difference of where exactly the western edge of a storm is. It just so happens that the storm is far enough east to put us right on that borderline between getting into that heaviest banding and missing out on the real heavy snow, and that is what all my time is currently concentrated on.
The next free update will be published around 8 PM.