Snow Prolonged Into Saturday

The Premium forecast, made available to clients, has been summarized and now freely posted below for the storm.  Premium clients will receive one final update around 10 PM diving in deeper again with the forecast, but the general idea should remain the same to the one posted below.  To subscribe to receive Premium email updates with for this and all futures storms, you can sign up here.  Otherwise, the forecast is attached below:

I’ll start with what the updated accumulation forecast is for the entire region.  Due to the heavier front end snowfall, amounts have been raised across the board to 3-6 inches of snow.  I don’t think there will be much of an inland/coast distinction in snowfall amounts because snow starts a little earlier at the coast but takes a little longer to turn over inland.  Thus, I will make the distinction that some areas far inland (primarily around/north of I-84) could see snow totals approaching 7 inches if everything comes together just right.  That will primarily be in New Haven County, and again that is not likely to be widespread.  Instead, a general 3-6 inches of snow looks likely.  It’s worth noting that the GFS model really only shows around 2-3 inches while the latest ECMWF tries to give the entire region 6-8 inches, so of course there is still quite a difference in what exactly occurs and the snowfall forecast remains quite volatile.  But what I see occurring is a general 3-5 inches of snow falling before 7 or 8 AM across the entire region with the first batch of snow.  Recent indications are that amounts will be closer to the 5 inch range than the 3 inch range, but that fits in well with the forecast.  By 8 AM the entire coast is turning over to that rain/freezing rain mix, which will be quite heavy at times.  Even the freezing rain will work to compact some of the snow, especially as temperatures look to rise above freezing.  The rain/freezing rain combination continues through at least 2 PM and surface temperatures remain above freezing through at least 4 PM, allowing some of the snow that has fallen to melt and compact.  I am estimating around 1-2 inches of snow that falls in the morning will be lost either to melting or to compaction (as the rain makes the snow heavier and denser it shrinks in volume), so that there will only be around 3 inches of a heavy wet snow on the ground come the changeover back to snow.  In the changeover back to snow, anywhere from another 1-3 inches of snow looks possible to accumulate, and although surface temperatures look to be above freezing I have a feeling that snow in this backside band will be heavy enough to overcome that.  Thus, by the time the storm is all said and done, we are looking to have around 3-6 inches across the region, likely a little less at the coast because temperatures will be higher and thus there will be more melting/compaction, with maybe isolated higher amounts far inland in New Haven County.  It will be a rocky road to get there, but we enter Saturday night with a snowpack to lower temperatures back below freezing and ice everything up.

As for ice accumulations, this part of the forecast is much harder.  Right now, I am looking for .05-.1 inches of ice at the coast and .1-.2 inches of ice inland.  In either scenario, this is fairly significant icing.  However, I think the icing and associated impacts are much more severe across inland regions.  There, surface temperatures look to remain below freezing longer and start colder.  For example, overnight tonight the coast only gets down to around 30 degrees or so.  That is below freezing, but it will not put so many surfaces in such a deep freeze that they remain below freezing as air temperatures slowly rise tomorrow.  So that by 9 AM, as seen here, the entire coastal plain should be turning to a cold, plain rain.  Air temperatures across the coastal plain remain above freezing it looks like through 4 or 5 PM, allowing road problems there to ease.  Again, it is important to note that for a majority of the timeframe, we are talking about the coast being anywhere south of the Merritt Parkway and temperatures generally look to range from 33 to 35 degrees.  This means that a slight last-minute colder trend could raise the coastal ice threat, and that even with air temperatures slightly above freezing icy patches could exist on roadway into the late morning.  So road conditions at the coast do look to start easing around 10 AM as temperatures rise above freezing, but they still remain potentially slippery through the day, and then between 3 and 6 PM they begin to ice back up with the final burst of snow and temperatures beginning to drop back below freezing.  Either way, if driving tomorrow, be sure to use caution, especially in the morning where back ice will be the biggest threat.  With surface temperatures and air temperatures right around freezing, treated roads will be significantly safer and should not see nearly as many problems as last week, as the salt/sand should be able to make up the necessary temperature differential.  Still, there is no guarantee that all roads are treated or that some isolated pockets are not icy, so definitely take it slow even if it just seems wet.

Inland areas are even more challenging.  By 1 or 2 PM there is consensus all inland areas will be above freezing.  But until then, things will get interesting.  Take a look at the ARW/NMM here.  On the left you can see the NMM for 11 AM tomorrow, where temperatures are generally 33-34 degrees across the entire region, but there is a small pocket of below freezing temperatures in the Newtown region.  That shows just how scattered/isolated icing issues could be late tomorrow morning into the early afternoon.  On the right, you see the much colder ARW.  It has the entire inland area below freezing still at 11 AM, indicating a very significant icing event is ongoing.  I think the ARW is overdone with its cold, and the HD NAM is certainly warmer, as seen by 10 AM here.  But you can see how real the inland icing threat is.  My current thinking is that inland areas go over from their snow around 8/9 AM, and all inland areas immediately begin as freezing rain.  This ices up all surfaces which remain below freezing, and so travel, which is already bad by 4 or 5 AM, goes significantly downhill by 8/9 AM.  Poor travel looks to continue at least until 10 or 11 AM, when the first regions start to rise above freezing and the ice begins to melt.  Some treated roads should be drivable then.  Any cold pockets continue to warm through 1 PM as freezing rain in areas turns over to plain rain.  However, anywhere after noon there are indications that far inland areas around or north of I-84 may actually mix in with snow through the eventual end around 6 PM.  This snow, with temperatures around or slightly above freezing, does not look to accumulate as much, as it will be mixed in with rain, but this explains why I am worried about isolated amounts up to 7 inches in far inland areas.  Road conditions will probably be best in that 1-4 PM timeframe across inland areas where there is the highest probability of surface and air temperatures being above freezing, so treated roads should be drivable as long as you use extra caution.  After that in the evening temperatures drop back below freezing and we will deal with additional icing issues.

CONCLUSION: Overall, a widespread 3-6 inches of snow is expected across the area, starting late tonight between midnight and 3 AM, turning over to freezing rain/rain between 7 and 9 AM and going to plain rain at the coast by 9/10 AM or so but taking until maybe 11 AM to turn to plain rain inland.  Sleet could mix in at any time as well.  We then go back over to snow by 3 or 4 PM and could get one very heavy burst of snow (talking around 1 inch per hour snow) through 6 PM, and by 6 PM it looks like all precipitation will swing on out of the region.  Ice accumulations at the coast look fairly minimal, maybe around .05-.1 inch before beginning to melt, and this will mainly be off treated roads.  Inland, icing could be more significant in the .1-.2 range, but could be less if inland areas stay snow longer or warm quicker at the surface.  There will likely be a period where very heavy snow falls across the region in the afternoon with surface temperatures above freezing, allowing road conditions to not be quite as bad and slightly limiting accumulations.  Premium subscribers will receive one more update in the coming hours, and I’ll then be back early tomorrow to track the progress and liveblog on Twitter, so be sure to stay tuned!

2 responses to “Snow Prolonged Into Saturday

  1. What are your thoughts on flooding at compo beach basin? and other coastal areas…perhaps as compared to Irene and Sandy.

    • Flooding does does not to be as bad as in Irene or Sandy, mainly as the storm is not tracking to our west which would pressure the water further north. Minor coastal flooding is likely. As of now the NWS has them as Coastal Flood Watches for tides 2-3 feet above normal. Possibility of 4 feet above normal could cause more issues, as that is close to the threshold I significantly worry about, but this should not compare to Sandy or Irene in terms of amount of coastal flooding.

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