First, I am raising the snow day percentage to 100%. With state offices being delayed until 10 AM (and very likely closed) and heavy snow continuing until at least 12 PM or 1 PM at the immediate coast followed by heavy rain/snow and horrible road conditions, I am confident in guaranteeing conditions for snow days across the entire region. Many districts have already closed and any that do not announce tonight should tomorrow. Of course for some reasons districts can have minds of their own, but conditions will be present warranting school closures tomorrow, of that I am certain and all guidance continues to point towards it. I will focus on Friday later tonight and in multiple updates tomorrow.
With the school forecast out of the way and quite obvious, I want to focus on a few other aspects of the storm that I am focusing on. The most important one relates to the 850mb low pressure center. Most low pressure centers I focus on are at the surface, because those relate to precipitation orientation, best lift, banding etc. However, low pressure centers can extend through all layers of the atmosphere. There is going to be one at around 5,000 feet in the atmosphere at the 850mb atmospheric layer. This is typically an important layer because it is where the best snow growth can be happen, and if the 850mb temperature is below freezing it is likely that we are seeing snow, vs. it being above freezing, which will likely result in rain or maybe sleet for a period of time tomorrow. Originally, it looked like the 850mb low pressure might stack on top of the surface low pressure center, but at this point it looks like it will be a little further west and not quite as strong, hence the updated timing forecast this morning. A weaker 850mb low pressure center will not pull in as much colder air. This will allow a period of mixing for most or all of Southwestern Connecticut, though it still does not change the accumulation forecast at all.
I want to delve into the timing of the storm again using 850mb low pressure placement. Of course, it is very clear that the entire region will start as snow. It continues to look like that changeover will happen between 12 PM and 1 PM for the immediate coast, and then progress inland. However, it could wait a little longer, with a few models colder aloft. The ECMWF weather model, for example, has the mix line wait until 7 PM to reach northern Fairfield County as it very slowly moves through the county. Thus, the immediate coast may mix with rain as soon as 12 PM or 1 PM but I think snow could stay in there through at least 2 or 3 PM. Not sure how much accumulates when mixed in with rain, but I think through 2 or 3 PM most of SWCT will continue to see snow falling outside their windows. Further inland, that snow could continue through 4 or 5 PM, maybe mixing with sleet and likely mixing with rain before then. It looks like then the 850mb freezing line will move north of the region and the entire region will turn to rain. The next aspect is always difficult, as models differ on when the cold air finally floods the region back behind the storm. Right now, it looks like between 11:30 PM and 2 AM we will see the freezing line move back through the region companied by a few hour burst of moderate to heavy snow that could drop another 2-4 inches of snow. Most surface will be wet, but temperatures will rapidly drop below freezing, especially in the heavy snow, and thus there will be very serious icing issues and likely snow-covered roads come Friday morning. That’s why the Friday school delay issue remains so large. I’ll now break down the updated accumulation estimates in each one of these timing ranges.
Between 2-4 AM and the 12/1 PM mixing time frame, I expect 5-8 inches of snow now to fall across the state. Models have been a little bit slower with the onset of precipitation and the heaviest precipitation. With mixed precipitation between 1 PM and 11 PM I see an additional 1-2 inches at the coast and an additional 2-4 inches. Then, as the final burst of snow moves through past 11 PM going through 4 or maybe even 5 AM, I see another 2-4 inches of snow. The final estimates then remain 6-12 inches at the coast and 8-14 inches expected inland. The additional couple hours of snow without as much mixing inland will likely equate to around 2 inches, hence the different zones, but I do not expect a very steep gradient with this storm as the mixing line will move through the area fairly quickly.
I also want to briefly touch on winds. Winds begin to pick up by 8 AM tomorrow morning, and they will peak between 10 AM and noon tomorrow along the coast. Current wind forecasts are for sustained winds around 25 mph with gusts to 40 mph at the peak, and sustained winds at 20 mph with gusts to 35 mph inland. The coast will not see gusts to 40 mph for long enough to warrant Blizzard Warnings, but blizzard-like conditions are looking more and more likely as gusty winds blow around this very heavy, wet snow. With temperatures so marginal, this snow will be extremely dense, and that is why isolated to scattered power outages remain possible. The main power outage potential will be between 10 AM and 1 PM tomorrow, so I will continue to monitor and update you on any outages that occur over Twitter. Winds then continue throughout the day, though, at similar speeds. Gusts to 35 mph could happen throughout most of the day and part of the evening at the coast, and even inland gusts to 30 mph with sustained winds in the 20 mph range will be regular. The duration of winds could also result in some isolated outages by evening, especially depending on when the turn back over to snow happens. Though the winds will not be the headlines as I do not expect them to exceed gusts to 35-40 mph, outages are a potential when combined with the snow, and it will be something to continue watching.
That’s where we stand with the storm and with the going forecast. The storm is coming to fruition, and the original accumulation forecast is still the going forecast for the region. The largest changes have been the burst of snow now expected overnight Thursday night and the slight increase in winds that bring power outages back into play. I’ll have another update at 9 PM where I go more into detail about what short range models are showing, as by then the first ones will begin showing when to expect a changeover to rain across the region. Make sure to keep it here for the latest Southwestern Connecticut weather breaking news.