6:00 PM UPDATE: 60% Snow Day, 40% Delay

Snow days are now forecasted for Wednesday, January 22nd across Southwestern Connecticut, mainly because of the enhanced mesoscale banding that is sitting across the region.  This blog post is going to go a little in depth as to what it means that this band is sitting over us with very heavy snow and how that is likely to impact snowfall amounts.  I’ll also go a little more in depth into the school decisions here as well.

First, I want to start by reminding you of that 20% chance I’ve had all along that my forecast busts high because the mesoscale banding sets up over Southwestern Connecticut.  Most of the guidance I was buying into, the guidance that has been most accurate and is best trained to pick up on mesoscale banding, showed the best forcing and vertical velocities over Long Island with decent forcing over the SWCT coastline.  That led me to believe that the heaviest snow bands would set up over Long Island and just graze Southwestern Connecticut, meaning a sharp gradient would set up with more snow at the coast than inland.  As late as the 12z RGEM run this morning had this setup.  Instead, that 20% chance looks to be coming true with some of the best banding setting up across Southwestern Connecticut.  This is resulting in snowfall rates of 1-2 inches per hour continuing for 4-6 hours, meaning that many areas could easily see 4-8+ inches of snow just in that small time frame.  The only weather models showing such a scenario were the SREFs from last night, with the GFS also showing something similar.  Ironically, both models lost the signature today, but that is exactly what happened.  Even short range guidance like the RAP and HRRR had the feature but then lost it; the banding decide to just come back even more intensely than any of the weather models had predicted.  The result is a longer period of truly heavy snow than I was forecasting, and so this doesn’t change the timing of the storm or extend it in any way, it means that snowfall accumulation forecasts will be adjusted due to the intensity of the band.

The going forecast was 5-10 inches of snow at the coast and 4-8 inches inland.  The 5-10 inches is going to be bumped up inland, though it only applies to anywhere south of Interstate 84.  The coastline we still believe will see slightly enhanced totals due to the orientation of the storm, so we are bumping that up to 6-12 inches of snow.  Not a major change, but this is just to reflect the additional 1-3 inches that the extremely heavy snow in the unexpected band have brought to Southwestern Connecticut.  Inland, localized areas of up 12 inches are not out of the question, and at the coast we could see snowfall amounts peaking in the 13 inch range, just over a foot, so that will be included in the forecast as well.  It is still expected that most areas along the coast will end up in the 8-10 inch range, solidly in the original forecast of 5-10 inches and also within the new forecast of 6-12 inches, but because of the band we wanted to show the potential for areas of slightly more snow and bump up the range just slightly.  Inland it is similar, as the banding did not drastically change the forecast but just bring a few more inches than were originally expected this early with the storm.  At first it seemed the storm would occur mainly in the overnight hours from 7 PM until 4 AM but now it appears it was an afternoon and evening storm, with the worst from 2 PM until 10 PM.  It was a similar amount of time, but more snow earlier just meant it was necessary to raise amounts slightly to compensate for the fact that mesoscale banding (which is almost impossible to predict more than 12 hours in advance if you can even do that) set up across our region.  In the end, Southwestern Connecticut may have some of the highest snowfall totals with this storm because of the prolonged period of very heavy snow we are currently experiencing.

Schools are now forecasted to close specifically because of this band as well.  Towns will be able to clear 4-6 inches ending around 1 or 2 AM in time for delayed openings, but clearing up to 10 or maybe 12 inches in areas in such a short amount of time will prove much harder.  Not only that, but with gusty winds tomorrow morning blowing that snow around and wind chills below 0 to as low as -10 degrees, it is hard to see why schools would open at all.  There remains a slight chance, especially in the northernmost areas by I-84 that don’t see as much snowfall, that schools are able to get away with just delays, and again this forecast does not mean that EVERY district is expected to close, as the percentage chance would need to be closer to 100% for that.  Instead, it means I believe a majority of the school districts will need to close because of the combined threat of the wind, the arctic air, and especially the large volume of snow and blowing snow that will make driving on roads treacherous through the morning tomorrow.

So that’s what I am looking at here.  In terms of timing I am confident that steady snow will continue until a least 1 or 2 AM, albeit light after midnight, and there could be another period of moderate snow from a secondary, shifting precipitation shield from the bombing low pressure center that moves through between 1 and 3 AM.  Snow winds down from west to east between 3 and 6 AM, likely too late for crews to clean it up in time for schools.  Eastern areas of my forecast zone may actually see flurries lingering until 7 AM, and when the snow ends you won’t even realize it right away because the powdery snow will be blowing in gusts to 25-30 mph.  I compared this storm often to January 2/3 in its formation because they did form very similarly, but with that storm most of the banding was offshore or over Long Island instead of over Southwestern Connecticut, and with this storm the banding is here instead of there.  Along with that, the winds come later with this storm allowing the higher ratio snow to be recognized, and temperatures are also even colder aloft.  Essentially, the bust that I had on January 2/3 when I forecasted too much snow, especially for inland areas, is being modeled here, because this storm is playing out similar to how I expected January 2/3 to play about 48-60 hours before the event.

So it is the enhanced banding we are seeing now over the region (which was a surprise) and the ratios of 15:1 or 20:1 (and in some cases even a little higher) which are allowing this storm to slightly over perform.  I will continue monitoring this banding and the progression and formation of the low pressure center to our south as it deepens and report back on what other forecast changes could result, but overall the storm is performing similarly to how I expected it to, just with the enhanced banding region ending up across Southwestern Connecticut instead of Long Island.  Weather is never easy to forecast because of things like this, and when this storm is said and done and we are comparing totals you will likely be able to see the difference that a thin band of 15-20 miles was able to make in accumulations just across our little stretch of Connecticut.  Keep it here as I continue to update the snow day chance and follow this storm closely, the next update can be expected between 8 and 8:30 PM.

2 responses to “6:00 PM UPDATE: 60% Snow Day, 40% Delay

  1. I live at the beach in Westport. How safe will driving be tomorrow or should I cancel my 3pm appointment in Weston tomorrow?

    Think your knowledge is tremendous. May I make a suggestion? You might think about changing your format so it is more helpful to your readers. Often, we want to know how the weather will effect us NOW or the NEXT DAY, and we only have the time for a quick viewing. Putting a concise 2 to 4 bullet points intro to each report would be very helpful..I understand you cannot be 100% definite, but if you told me, for instance:

    *Midnight to 6AM prediction: 6-10 inches in FF county * AM diving tricky; stay off the roads if you can * 50% likelihood your kids with start school 2 hours late * Driving improves after 2pm tomorrow.

    Or in better weatherese. Thanks for your work.

    • I think by 3 PM roads will be clear enough that it would be reasonable safe for travel to Weston. I think most road issues come before noon tomorrow. And thank you for the advice! On the right hand side I have the “Winter Storm Update” box that is supposed to act as just that; a concise place to check for what the next storm will bring. I could definitely be more specific labeling at what times traffic will be impacted the most, etc. If you have any additional advice as to what I could add to that box please let me know!

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