Light Snow Expected Tomorrow

The below blog post outlines our free forecast for the storm that is expected to move through tomorrow.  Our Premium subscribers received a more detailed blog update that is summarized and emailed directly to them including forecasts for school impacts tomorrow and the latest details for the weekend potential winter weather storm.  To try out our Premium service, click here.  Otherwise, the free weather forecast for tomorrow’s event across SWCT/NY is below.

We’ll start with the storm threat for tomorrow.  Generally, I expect this to be a very low-impact threat for a number of reasons.  Snowfall accumulations will be minimal, snow will struggle to stick with warm surface temperatures, and the storm will be quite quick.  With that said, there are still a couple different ways that the storm could play out which I wish to cover here.

First, the accumulations: the forecast is for less than 1 inch of snow across all three counties anywhere South of Interstate 84, with a coating-2 inches forecast north of I-84.  Anywhere South of the I-84 will see temperatures above freezing throughout most of the storm, meaning that snow will struggle to stick initially, especially at the coast.  In fact, coastal areas may see a mix of rain and snow with surface temperatures near 40, and it could even start as all rain, essentially eliminating any chance of accumulations.  Even if the storm is all snow, the warm surface temperatures will greatly limit any accumulations.  Further inland, temperatures are closer to freezing, allowing snow to stick more.  Similarly, further inland, especially by the Litchfield Hills, will see what is called orographic lifting, where slight geographic lift helps enhance the rising moisture in the atmosphere and causes slightly more precipitation.  We can see this clearly on the simulated radar from the 12z NAM weather model for 3 PM tomorrow here.  We see snowfall beginning across all of Litchfield County and moving towards northern portions of New Haven County.  Meanwhile, lower elevations in Fairfield and Westchester Counties are still seeing absolutely nothing.  This is expected due to the higher terrain further inland.  It is that higher terrain that will both slightly enhance snowfall and keep surface temperatures slightly lower, allowing for accumulations potentially slightly above an inch.  Some areas along the coast may not see any accumulations at all as the snow struggles to accumulate.

So let’s detail the timing.  Generally, snow looks to overspread the region between 2 and 4 PM.  It should start earliest further inland, where we will see some of that lift.  However, surface temperatures at 3 PM do not look that conducive for snowfall, as seen on the 12z NAM here.  Coastal regions are in the low 40s, while the freezing line is all the way up in northern Litchfield County.  This means that at 3 PM, very few portions of SWCT/NY will see any snow sticking, even if it is snowing.  When the snow begins to pick up, we will see surface temperatures gradually cool off.  This is seen on the same model here at 6 PM, where the freezing line is still up in Litchfield County but temperatures are in the low 30s inland and in the mid 30s at the coast.  Still, it will likely take until 8 or 9 PM for most of the region to see temperatures fall below freezing.  As can be seen, by 7 PM the line of snowfall will rapidly be moving off to the east, as seen here.  This gives us a very narrow window where surface temperatures will be cold enough for snow to stick across the region and for snow to actually be falling.  The NAM shows the heaviest snow falling between 5 and 6 PM, as seen by the 6 PM output here, and that is generally what I am tempted to agree with the most.

One of the highest confidence aspects of this storms is the warmer surface temperatures.  On two short-range models here for 4 PM tomorrow we can see that temperatures are in the mid to upper 30s across the entire region, with the freezing line clearly off to the north.  Similarly, the operational GFS here shows temperatures in the upper 30s at the coast and mid 30s inland come 4 PM, when the brief burst of steady moderate snow will be beginning.  All models agree that by 7 or 8 PM a rush of colder air will be taking over and we rapidly fall below freezing, but that is too late as the cold air essentially dries out the atmosphere and there is unlikely to be much precipitation overnight.

Now, there are still a couple risks to the forecast.  Should the storm trend much colder (very unlikely) then travel could be worst on the day on Tuesday.  That’s unlikely.  The only way I could see that happening would be if snowfall got heavy enough to pull down the colder air from aloft, which is possible inland with some of the orographic lifting but seen as extremely unlikely at the coast.  The main risk here is that the Clipper does move either a little faster or strengthen a little quicker.  This could allow snowfall to either be slightly heavier than forecast (which the RGEM regional Canadian weather model shows as a risk here) or start a little earlier than 1 or 2 PM, messing with snowfall totals and surface temperature conditions.  These are things that I will be watching very closely on short-term model guidance both overnight tonight and into the day tomorrow, as these Alberta Clippers are known to hold a number of surprises and can sometimes cause surprise travel trouble even when they look as harmless as they do on most weather guidance right now.

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