FREE: First Official Wednesday Snow Threat Forecast

Our first free official forecast is now available.  A reminder that for earlier access and for the more detailed forecast, alongside impact analysis (including snow day forecasts and travel expectations), you may subscribe to our Premium service or purchase the individual premium forecast here.  But, as was promised earlier this season, we wished to still provide in-depth, free forecasting as well, so this will hopefully serve to be some of the most detailed forecasting expectations for the upcoming storm.  We detail both accumulation and timing expectations for the storm, and I provide a little extra analysis on snowfall ratios and possible updates to this forecast as the storm approaches.  So I’ll dive right in:

SNOW ACCUMULATIONS: The going snowfall accumulation forecast is as follows: All towns removed from the coast (not bordering the coast) may expect somewhere in the range of 6-10 inches of snow.  Towns north of Interstate 84 could see isolated amounts up to 12 inches at the peaks of their hills, but even up there I do not expect much more than widespread 6-10 inch amounts.  The storm is too quick-moving for extreme accumulations as there is not sufficient blocking, and lower ratio snow closer to coast will cancel out any additional liquid that falls.  In coastal towns, widespread amounts of 4-8 inches of a heavy, slushy snow are expected.  However, south of Interstate 95 the snowfall forecast drops to 3-6 inches of snow, as the boundary layer warmth is likely to make a difference in that region.  And at the immediate coast (literally within a few hundred feet of the beach) I am expecting 2-4 inches of slush.  What this means is that some coastal towns could literally see a spread of accumulations from 2 to 8 inches of snow inside their individual town, something that, while ridiculous sounding, is plausible and has occurred before.  What I am most confident in at this time, though, is that everyone, all the way down to the coast, will see accumulating snow from this storm.  Similarly, I am confident that the Winter Storm Watch will have to be spread to coastal towns for the regions there north of Interstate 95 where enough heavy snow will stick for areas to hit 6 inches.  It is also worth noting that, on average, New Haven County is likely to see about an inch more than Westchester County.  New Haven as a whole being further north may be enough to make a slight accumulation difference, though this will mainly be seen in inland areas.  I dive into this difference more on the Premium site, but figured it would be worth pointing out here as well.

TIMING/PRECIP TYPE: With the all important accumulation forecast out of the way, I want to turn now to timing of the storm.  As with accumulation, models continue to jump around with timing.  I won’t delve into the details as much as I want to first present an overview of timing, but the expectations is that precipitation begins around 5 AM across most of the region as a rain/snow mix.  Coastal towns may actually start as all rain or rain/sleet at the onset, whereas inland areas are more likely to have snow mix initially.  Through around 7 or 8 AM precipitation will pick up slightly in intensity, and by 8 AM or so inland towns should be seeing all snow.  At the coast, 8 AM marks the point that snow begins to significantly mix in.  By around 9 or 10 AM precipitation is now moderate in intensity and inland snow has begun to stick on grassy surfaces and untreated roadways.  At the coast we are now all snow, with areas north of I-95 seeing snow begin to stick on grassy surfaces and areas south of I-95 likely seeing that snow melt on impact.  By 11 AM or noon the heaviest precipitation will be moving through the region, and the entire region should be all snow.  Some sleet could briefly mix in across New Haven County and coastal Fairfield/Westchester County, but snow will be the predominant precipitation type at the peak of the storm.  It is in this window from noon until 6 PM that the majority of the accumulations will occur, especially in coastal areas.  Snow sticks by noon even by the beaches, though it may struggle to stick on warmer roadways, staying mainly by the sand/grassy surfaces.  Anywhere north of I-95 is likely to see driving conditions significantly deteriorate by noon (if they have not already) as the snow is heavy enough to overcome any warmer roadways and stick on contact.  It may be slushy vs. icy, especially on treated roadways, but it is still likely to cause problems.  The storm looks to end as snow as well (this isn’t one of those where only the heavy precipitation is snow), and snow winds down from west to east between 6 and 10 PM.  Some lingering flurries could continue until around midnight, but accumulating snow is almost guaranteed to wind down by midnight, allowing the cleanup to begin overnight for Thanksgiving day.  That’s my general expectation on precipitation type/timing of the system as a whole.

ADDITIONAL ANALYSIS: In terms of when travel would be preferred over not, or what this means specifically for inland and coastal schools, that is all detailed in the Premium section.  I do want to point out why I have a slightly more extreme gradient in the forecast here than others, though.  I first published this forecast on the premium site around 3 PM, and around then it was considered one of the more snowy forecasts.  Over the ensuing 2 hours, model guidance came out in line with my expectations, and the National Weather Service and other outlets have similarly upped their expectation for the Connecticut and New York region.  This is due to a number of factors, including dynamic cooling (strong precipitation and lifting helping to cool the atmosphere, understood simply), a stronger arctic interaction, and the slightly lower sun angle coming in November than in, say, October, like in the October 2011 snow storm, which was actually used as a basis for a decent amount of this forecast.  Still, the forecast I have presented now has a sharper gradient than many…I see forecasts for up to 6 inches of snow right down to the immediate coast.  And this is certainly possible, especially if the storm slightly deviates to the east or is stronger than predicted so it can pull in more cold air.  But with ocean temperatures still fairly warm and surface temperatures still marginal (the immediate coast may never drop down below freezing throughout the storm), I see it hard for those regions to get to 6+ inches of snow.  Realize, this is seriously the immediate coast, and many areas, especially inland, are expected to see much more than just 6 inches of snow, but coastal areas are likely to see less than inland areas as a gradient sets up.

I also need to emphasize, too, that this is not a matter of liquid equivalent or amount of precipitation.  In fact, it is likely that coastal areas see more liquid fall in this storm than inland areas do.  There are a couple factors that will still limit coastal accumulations, however.  The first is that precipitation likely starts as rain across the region.  This gets the surface wet, and without sustained temperatures below freezing at the surface you have to wait for the heavier snow before it can easily stick.  What this means is I am looking at about an inch of liquid equivalent falling in most coastal areas.  The first tenth of an inch likely falls just as rain or as a rain/snow mix.  The next tenth of an inch or two likely does not stick at all, and then after that you are dealing with ratios as low as 5:1 or 6:1 at the coast.  The result is it gets hard to see how immediate coastal areas see more than 4 inches of snow, with areas south of I-95 struggling to get above that 6 inches of snow.  North of I-95, however, and it is a different story with snow sticking earlier and having ratios of up to 9:1 or 10:1.  As it is, the 18z GFS weather model just came out showing liquid amounts of generally .8 or .9 inches.  That fits in well with my forecast, as inland I expect snowfall ratios of around 10:1 and almost all snow, so up to 8 or 9 inches, with maybe 10 inches in a few locations.  Still, I doubt many areas in the state see more than 10 inches of snow, as there is just not the liquid from this storm to support it due to its quick-moving nature.  So while liquid amounts will be fairly confident, with a little more at the immediate coast, boundary layer temperatures there are much more marginal, limiting potential snowfall accumulations.

That’s really the main update that I have for the upcoming storm, and I would classify confidence as moderate with this going forecast.  I will continue to update as necessary, with maybe one more free update later this evening before numerous updates are published tomorrow.  Remember, for continuous coverage along with impact analysis/school forecasts (plus detailed 7-day forecasts and regional 15-day forecasts) be sure to sign up for our premium service and be even further ahead of any storms heading into the SWCT/NY area.  Keep it here for the latest!


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