First Accumulating Snow For Many Inbound

This will be one of our free posts for the upcoming snow event that will be impacting the region.  Our free posts we generally like to focus specifically on the going forecast and some go the model guidance behind it.  The Premium subscription service we offer takes it one step further, offering impact analysis of what we think school districts will do in response, what road conditions will be like, how flights will be impacted, what investment impacts there could be, and then we go further in-depth showing the images of the associated weather models.  To sign up for the Premium service, simple click here.  Or to buy the most recent Premium forecast that includes our delay percentage chances, please click here.  If not, I’m going to dive into the forecast here:

Rain is already breaking out across the region.  This is not surprising, as often with storms of this nature where we have some weak overrunning precipitation ahead due to some atmospheric forcing/lift, we see precipitation form ahead of what the models say.  This time it is happening a couple hours early, in line with expectations.  Over the next couple hours we will see surface temperatures continue to drop.  5,000 feet in the atmosphere temperatures just dropped below freezing, and that will likely translate down to the surface in the next 12 hours.  The result is that anywhere north of the Merritt Parkway/Hutchinson parkway will be below freezing by around 6 AM.  However, that is after the snow moves through.  But, before we jump ahead, I want to outline this transition.  Probably around 8 or 9 PM, we see far northern parts of Fairfield, Westchester, and New Haven counties begin to transition to snow.  It takes a few more hours before temperatures up there drop below freezing and that snow begins to stick.  Probably around 11 PM to midnight we start to see snow sticking inland, and right before then is when closer to the coast we see the rain turn over to snow.  I expect by 11 PM or so even the coast will be seeing snow, though it will still be in the mid to upper 30s so I doubt it will be sticking.  By that point, upper levels of the atmosphere will likely be cold enough, though, and the surface warm layer small enough that snow can fall all the way down.  It likely takes until 2 or 3 AM for coastal areas to begin seeing any accumulation, if it sticks at all, but farther inland is when it happens earlier.

So, we have snow start sticking inland around 12 AM and precipitation moves out of the region around 5 AM.  That’s 5 hours with the potential for accumulating snow by Interstate 84.  Snow will generally be falling at rates up to a third or half an inch per hour.  Doing our the math, that’s the potential for 2.5 inches of rain should the heaviest band of snow train over an inland area.  At the coast, there will only be a couple of hours of snow sticking if it does at all (the immediate coast is where it is most unlikely), but we would not be surprised if a heavier burst of snow did swing through and coat everything down to the coast.  So that helps explain the going forecast: coastal areas south of the Merritt/Hutch can expect up to 1 inch on grassy surfaces, but it is unlikely that it covers many roads or accumulates more than an inch.  Some areas may not see accumulations at all, especially at the immediate coast.  In between the Merritt/Hutch and Interstate 84 the forecast is for up to 2 inches of snow.  Right around the Merritt/Hutch is where there is a chance for little to no accumulation or just a coating, while up by Interstate 84 is when it is possible to get those 2 inch figures, especially on elevated grassy surfaces.  North of I-84 the forecast is for 1-3 inches of snow; we expect snow to stick early enough that most locations up there will see at least an inch of snow, and isolated amounts of up to 3 inches are possible given the amount of precipitation that will fall.  Still, 1-2 inch amounts are expected to be much more widespread, I just would not be surprised to see isolated locations exceed that 2 inch amount.  So that’s the going accumulation and timing forecast at this time.

I do want to go a little more in depth on this storm here, although there isn’t much else to really go over besides the forecast.  The main impact analysis (again, the focus of the premium site) is that there will be a period of time where farther inland snow is falling with temperatures below freezing, and even where snow melts on contact with roads if the roads are wet and untreated and temperatures drop below freezing we could be dealing with a few hours of black ice.  Hopefully, as I expect is the case, towns are aware of this threat, even though it appeared fairly quickly, and they will treat major roadways so there should not be too many issues.  South of 95 it is unlikely that temperatures even drop below freezing, so I doubt there will be any road conditions at all there.  Also the highest chance of no snow sticking there.  But it is inland, from I-84 on north, that the largest chances of impacts are held, and again on the Premium site we have a lot of content devoted to that region due to what we see coming.

Weather models are in general agreement of the forecast I have lined out above.  I go very in-depth on the Premium site with this idea that weather models are over-estimated the amount of time that the storm is rain versus snow, but I want to outline that here.  It actually makes no accumulation difference, but we are dealing with a very strong cold front that will cool the upper layers of the atmosphere much quicker than at the surface (less friction up there so the colder air can flood in and rush through faster).  Thus, though models show temperatures in the mid to upper 30s at the surface later tonight, the warm layer will likely be shallow enough that the snow does not melt on its way down.  Instead, it falls as a very wet snow and melts on contact.  In some of the heavier bursts, it may briefly cover grassy surfaces before melting.

Finally, by 6 or 7 AM tomorrow the sun will come out, and that will quickly melt all the snow, even inland.  Temperatures remain below freezing inland through around 8 or 9 AM, but even direct sunlight with temperatures below freezing will melt snow, and then once temperatures rise above freezing and get into the 40s we will see all the snow melt.  This storm is really just a sign of what is to come in the future, swinging through overnight with maybe enough snow in places to be a nuisance, but won’t leave much a trace.

That’s it for the free update, and I plan on posting another one later tonight as the storm develops.  I will continue to update the sidebar with additional small thoughts and free content as well, and will let you know if the Premium impact analysis significantly changes.  So be sure to keep checking back here and consider upgrading to a Premium subscription (10% off with the coupon code “weather”) where the content goes more in-depth, is updated more regularly, and offers impact analysis of how exactly this storm could impact your individual life.  Stay tuned!

 

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