7 PM UPDATE: Snow Storm Round Two: 55% Snow Day Chance Inland, 45% Coast

Here we go.  Round two starts tomorrow morning, and it will be all snow.  And it will be a quick hitter.  Tonight I actually mean it when I say that this is the first of many updates because this is such a low confidence forecast that it will actually need multiple updates.  What is happening is a weak wave of low pressure will move along the stationary front to the south and with that will enhance dynamics across the region causing a strong band of snow to move through, likely between 9 AM and 3 PM.  Strong forcing will cause the snow to be moderate to heavy at times, but it is unlikely that the snow will go for more than 6 hours.  At the same time, the timing makes it just right to potentially close schools as it will be happening right in the middle of the day, with the worst from 10 AM to 1 PM.  Hence the heightened snow day chances for a storm that will not last long and not drop huge amounts of snow.

I want to start with a very important message for anyone involved in decision-making for schools tomorrow: do not issue Early Dismissals.  If you decide to open schools, which is not necessarily a bad decision given some recent trends I am following, do not be persuaded by the heavy snow that will begin around 9 or 10 AM to let schools out early.  Students will be let out into the worst of the conditions.  By 2 or 3 PM the snow will end and conditions will likely begin to improve fairly rapidly, especially if roads are being treated throughout the storm and they had been properly salted.  If anything else, I encourage you not to fall to pressure and call an Early Dismissal that would likely be worse than letting schools out early.  This timing difference is why there is not really an Early Dismissal chance yet with the storm, while the snow day chance is fairly high. 

Now for the details of the storm: Snow will begin to break out across the area likely between 8 and 9 AM from west to east, with the snow really picking up just past 9 AM.  Snowfall rates will start around half an inch per hour and peak around an inch per hour.  It is interesting to note some pretty large model differences in precipitation amounts.  They all seem to agree on timing, hence why I am so confident including almost exact timings of snow to begin and end, but the amounts I haven’t mentioned yet because it is much more tricky.  Model disagreement is in two camps here, we have the NAM/GFS camp on one end, the SREF/GGEM camp in the middle, and the ECMWF/UKMET/NMM/ARW camp on the other end.  The NAM/GFS have the most precipitation, bringing up to 5-6 inches into the region tomorrow in strong banding.  I don’t buy that.  The ECMWF/UKMET/NMM/ARW camp brings as little snow as an inch or two, which I also think is a little low but is also certainly possible.  So in the middle we get the SREF/GGEM camp, which is the one I trust the most.  If the NAM doesn’t have the most QPF for the storm, which it does not, I tend not to trust models that have more, so the GFS has been discarded.  I like this average because there is a battle between great forcing and dynamics from this wave, something we didn’t have with the last storm, but there is also again a lot of very cold, dry air that could keep the bulk of the precipitation just to the southeast of the region, like some of these models show.  Experience tells me that this time of storm COULD over-perform but more times than not the dry air will at least play some role.  There will be a single band of heaviest snow, and if that sets up over the area then we could see amounts widespread of up to 4-5 inches, but right now I think a base of 3 inches is best for the storm.  This snow will be slightly more powdery than normal because it will be cold dry air that the precipitation will be forcing itself over, and ratios may be slightly higher than 10:1 for most of the storm, maybe 12:1 to 15:1, which also could help increase amounts to close to 3 or 4 inches even without the larger amounts of moisture that the NAM and the GFS show.  Still, I am going with a general 2-4 inches with locally up to 5 inches where the best mesoscale banding sets up tomorrow, which I do think could be somewhere either over or near Southwestern Connecticut.

What this means for schools is tricky.  Obviously, there won’t be any problems getting to school.  Leaving school is the problem.  With the predicted worst snow from 10 AM – 1 PM and snow ending up 2 or 3 PM from west to east, early dismissals should be off the table.  The question really is whether the district is confident enough in its ability to remove a quick falling 2-4 inches of snow from the roadways during the day to lead to safer roads in the evening.  The reason I distinguish between inland and coastal areas actually has nothing to do with weather; it is mainly because inland communities tend to 1) be colder and thus have icier roads but mainly 2) tend to be hillier, making roads more treacherous in snow, which leads to them having an easier time closing.  That is why I am currently forecasting for snow days in inland Southwestern Connecticut, while I am not at the coast.  However, this is far from a blanket call.  This storm is marginal enough that it really is a case-by-case call for each town.  Towns with records of not closing easily and having strong Public Works departments, like Greenwich and Westport, are not as likely to close as towns that tend to close slightly more easily, like Fairfield or Norwalk.  Inland towns are no different, though closures are likely to be slightly more widespread there, even if they don’t get quite as much snow as the coast.  If anyone gets 5 inches of snow, it is likely to be south of Interstate 84, and more likely just north or close to the Merritt Parkway.  Anyway, at this time the storm seems marginal enough for me to forecast the snow day percentage right around the 50% line both at the coast and inland, and over the next few hours I likely will continue to refine it.  A lot can change in the 9 hours before the decisions to stay open or close are made, so definitely be sure to keep it here for the latest on these changes.  Also be sure to do your homework tonight, as there are not going to be any guaranteed snow days in Southwestern Connecticut, even though there is of course a very real chance of schools closing.  This is just the latest I am seeing from the data coming in, and there is also a very real chance that these percentages will rise in the next update, which can be expected between 8 and 9 PM.  Keep it tuned in here for the latest on this snow storm!

One response to “7 PM UPDATE: Snow Storm Round Two: 55% Snow Day Chance Inland, 45% Coast

  1. Hi. Add this to your model. Greenwich already has a early release in place for elementary schools for parent/teacher conferences, possibly forcing them to call the day for the district. Thanks for your great work!!

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