5:15 PM UPDATE: Northwest Trend Brings Snow: 30% Delay (coast) 20% Delay (inland)

A strong coastal disturbance to the south of Southwestern Connecticut will be moving offshore tonight, and you’ve likely heard a lot about it in the news the last few days as it brings heavy snow to Georgie, the Carolinas, etc.  The precipitation shield with this storm has trended slightly northwest in the last few model runs, though not quite enough to bring significant snow.  What will happen is most of Southwestern Connecticut will just get scraped by the edge of this precipitation shield.  The shield will be entering into extremely dry and cold air, meaning that some precipitation may not reach the ground as it evaporates while falling (this is called virga) and what does reach the ground will be extremely fluffy, dry, and stick to everything instantly.  You know the deal after the last few storms.  The going forecast is for widespread amounts of a coating-2 inches of snow.  It could start as early as 11 PM this evening, though the moderate snow (if there is any) will fall between 1 AM and 4 AM.  Snow showers could continue until as late as 6 or 7 AM in some areas.  To break this down more, anywhere east of Route 7 and south of the Merritt Parkway is most likely to get over an inch of snow.  Anyone west of Route 7 and north of the Merritt Parkway is likely to get an inch or less.  Anyone near or north of I-84 would be lucky to get more than a coating.  The precipitation shield is quite literally barely scraping the region with snow, and thus every few miles closer to the storm center passing to our southeast will add extra time to the snowfall.  That is why more southeast regions are likely to be impacted by the snow.

What this also means is that there could be some school delays.  Obviously I do not believe that a coating or a half of an inch of snow ending by 4 or 5 AM should warrant delays.  But there is an outside chance that the precipitation shield jogs just a few miles northwest and some areas could see as much as 2 inches of this light, fluffy snow.  Because it is so cold, snowfall ratios will be very high (20:1 or higher).  Whenever there is extreme cold snowflakes form more complex shapes and require less moisture to form and thus stack easier (I’ve gone over this many times).  This will happen again, and thus any snow that does fall will stack quickly and will be able to literally be blown off driveways, etc. by leaf blowers.  This is why up to an inch or two is possible, as it is very unlikely liquid amounts of over a tenth of an inch are realized, but even .05 inches of liquid could become an inch or more of snow with this precipitation shield.  One thing throwing a wrench in this forecast is the abundance of extremely dry air with this storm.  There is a chance that the majority of precipitation actually ends up being virga, so very little reaches the ground and even the coast only gets a coating.  That’s why I’m not specifying exact regions of snow, instead just saying a general coating-2 inches with the higher amounts likely west of Route 7 and south of the Merritt.  There are a lot of factors here because this is such a small, marginal event that all depends on exactly where this swath of precipitation goes.  It’s very possible areas near I-84 see no snow at all tonight.

So now I come to school impacts.  Obviously, areas inland that see a coating or no snow at all won’t need to delay.  Really it is only the inland towns that are one town removed from the coast that have a realistic chance of delaying unless there is more of a shift inland with the precipitation shield here.  But even then, inland areas are very unlikely to see more than a half inch or MAYBE an inch of snow, and snow should wind down by 4 or 5 AM.  Thus I have the chance of a delay at 20%.  At coastal locations, especially those further east (essentially Westport, Fairfield, Bridgeport on east) there could be a slightly longer period of precipitation that could be at a slightly higher rate.  That is why the coastal chance of a delay is 30%, because there could be up to 1-2 inches of snow and it could last until around 6 AM.  2 inches of snow ending at 6 AM is enough for a delay 9 times out of 10 in most towns.  1 inch of snow is a much harder call but a few towns could still even delay with that.  Thus, there is a realistic chance of a delay for coastal school districts now that is slightly higher than those inland.  Again, if there is another shift northwestward on the very short range guidance even inland areas could have enhanced chances of delays.  For now, I don’t expect too many changes in these percentages, but I will continue to keep an eye on the storm throughout the evening.  The next update will likely come between 7 and 8 PM so make sure to check back for that and keep it here to see if your school district is more likely to delay!

2 responses to “5:15 PM UPDATE: Northwest Trend Brings Snow: 30% Delay (coast) 20% Delay (inland)

  1. As always Jacob, thorough, fact filled and much appreciated .

  2. As always Jacob: thorough and fact based! Thank you

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