Light Snow Possible Friday

Light snow may threaten the region late Thursday into early Friday.  Premium members just received a detailed analysis of how it could impact schools and travel on Friday, and they will receive numerous updates to this impact analysis forecast through the day tomorrow.  To subscribe for the Premium service, please click here.  Otherwise, please enjoy the latest free update on the storm threat Thursday night into Friday that outlines the various weather model scenarios.  We will be releasing a free forecast if need be tomorrow afternoon on this threat:

Models are absolutely all over the place (as can be expected with these convoluted small-scale systems).  Some models give us 2-4 inches of snow, and others give us absolutely nothing Friday morning.  As of right now, I am more tempted to lean towards the scenarios that give us little to no wintry precipitation (as I’ll explain) but I also won’t rule out any of the scenarios that are currently on the table.  Generally, it is the American models that show the storm sliding out to sea and the international models that show more direct impacts, though of course it is never quite that easy.

Let’s begin with the SREFs, which do show some light snow.  On many models it is difficult to discern total precipitation from the storm as they are also forecasting for the rain continuing through the night, but luckily the SREFs give us percentage chances of snowfall accumulation as well.  Overall, the SREF probabilities actually look relatively reasonable.  As seen here at 7 AM on Friday the models give the region around a 25-35% chance of accumulating snow, which seems relatively reasonable given the spread of solutions currently on the table.  As we can see, by 10 AM on Friday that chance is decreasing in the west but actually increasing across eastern New Haven County here.  The model also forecasts probabilities of total snowfall accumulations (based off the individual members).  We can see here that through 10 AM on Friday there is around a 25% chance of an inch or more of snow across Fairfield and Westchester Counties, but that chance increases to about 30% across New Haven County.  This is not all that significant, but if an inch of snow were to fall it would certainly be noteworthy.  We can see that there is only around a 5% chance of 4+ inches of snow, meaning confidence is relatively high that this will not be a moderate or heavy event and that if we do get snow it should just be light.

Now let’s go through some of the other American models.  The NAM, which did relatively well with the last storm and typically is too amplified, actually shows the storm entirely missing.  On this output for 4 AM Friday we see that the precipitation is just getting into Rhode Island and grazing Long Island.  Also note that surface temperatures across the region are only around here.  The HD 4km NAM shows slightly more precipitation, as seen on its wintry accumulation output here.  We would generally expect less than an inch across the entire region, with a coating in southern Fairfield County and across much of New Haven County.  Any amounts of an inch or more would be in far southeastern CT into Rhode Island.  This is certainly a plausible scenario, and until yesterday models agreed relatively well on this.

Two other HD models, the ARW and NMM (which also performed decently with the last storm) also show the storm generally missing, as seen here at 5 AM on Friday.  The NMM, which has a bias to show too much precipitation, does show some briefly moderate snow moving into New Haven County, with a brief burst of snow possible in eastern Fairfield County.  The ARW, meanwhile, shows no threat of any snow whatsoever, as seen by their forecast wintry accumulations here.

Also in this camp is the GFS, which shows the snow slightly closer than the NAM but still just missing offshore, as seen at 4 AM here.  Again, surface temperatures are shown being around freezing inland and in the mid 30s at the coast, so if it were snowing it may struggle to stick at the coast but should be able to stick inland.

So with all these models not showing the storm, why the concern?  Well, two major international models, the Canadian and the European, both show decent accumulations.  The short-term RGEM here shows around an inch of accumulation possible across the entire region through 7 AM on Friday with slightly more possible from here off in New Haven County.  This model did struggle with the last storm but generally handles these small-scale storms relatively well, which is why I have been watching it so closely.  The lower-resolution Canadian model, which goes out past 7 AM Friday, is more aggressive, actually showing widespread snowfall amounts of 2-3 inches by 7 AM on Friday, as seen here.  This is some of the most aggressive guidance, and had previously been discarded before other guidance came in line.  The 12z ECMWF here shows the elongated low pressure center offshore much closer to the East Coast as well.  It actually looks similar to the CMC guidance with 2-3 inches relatively widespread.  Of course, more will be in eastern regions across New Haven County while the least should be across Westchester County; essentially the opposite of the last storm.

With that, I’ve outlined the majority of weather model guidance, and you can see why forecasts for this are changing so rapidly, and why confidence in what exactly plays out from here is so low.  Another update will come tomorrow detailing the latest forecasts and where confidence now lies.

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