Well, this update is coming much later than I had originally attended, but as I often say with weather, “better late than never.” I plan to briefly outline expected timing and precipitation amounts/timing from the storm, with of course more details throughout the day tomorrow as the storm unfolds. I’ll start with a brief summary, then break down timing, and then end with a brief description of where the models stand and what they each say in terms of total accumulations and thus total impacts, along with how school will be impacted.
For the forecast, I am sticking with my general 1-3 inches at the coast, and inland thinking something more along the line of 2-5 inches up to I-84. North of I-84 isolated amounts could be higher, but once again it is that warm nose that will result with a lot of mixing with sleet fairly on in the storm, meaning roads may be icy but total snow accumulations will really be held down. As for ice, south of the Merritt we are looking at a coating-.2 inches, and north of the Merritt I see from .15-.4 inches. Locally higher amounts are possible depending on the amount of cold air captured by the weak-but-strengthening low pressure to our south.
Now let’s get into some of the specifics. In terms of timing, models agree on precipitation generally breaking out between 4 and 7 PM across the region, with isolated snow showers possible before then. Precipitation will start out as all snow, and will begin sticking, probably down to the coast, by sundown around 6 or 7 PM. All snow accumulations are expected through around 11 PM at the coast, at which point enough sleet/freezing rain will be mixing in to really hold down additional accumulations. Inland, sleet may wait another hour or so, but by midnight I really see most of the region as sleet with snow occasionally mixing in. Between midnight and 2 PM the warm nose will widen enough aloft (the warm nose is centered between 775mb and 850mb, with the NAM having it further aloft than most other models) that all precipitation will be falling as rain. Depending on surface temperatures, it could be freezing rain or regular rain, as surface temperatures look to be either 32 or 33 degrees at this point. It really is too early to tell where that 32 degree line will be at the surface, and it will make a fairly significant difference. After 2 or 3 AM, almost all precipitation across all of SW CT will be either rain or freezing rain, so all accumulations of snow will cease and we are looking to begin icing. The further north you are, the more ice you should expect and thus the worse the roads will likely be for the Tuesday morning commute. Accordingly, the further north you are the better a chance you have for at least a delay on Tuesday, if not a snow day due to some serious icing. Precipitation thens goes over to all rain for all of SW CT at some point on Tuesday.
As for total accumulations, I went over that in the summary, but again a lot of it does depend on the progress of that warm nose. The GFS has it more around 810-815mb, the NAM is strongest between 775-800mb. In reality, it won’t make much of a difference, as I don’t think height of the layer will determine speed, but models do differ with speed. The forecast above is the general consensus that they have at this point, and this would mean that most likely, schools on the coast open on time, and schools inland end up being delayed to make sure roads are sufficiently treated from the ice. By 7 or 8 AM I do expect almost all of SW CT to be above freezing, unless the secondary low pressure strengthens much faster than expected. The 18z NAM had a solution like this, but at the surface it does have a fairly cold bias, and the 0z NAM backed off the solution, which was more of an outlier. Granted, the RGEM remains quite cold at the surface, and that even has a warm bias, making it even more confusing, but I do actually like the 0z NAM as a model for the storm, as I think it is getting ahold of the system quite nicely actually.
I will have many more details on this tomorrow, as well as continuous coverage on Twitter. While this is not a major storm, it could catch many off guard, mainly because it is in mid March and we are dealing with sleet/ice, which is not as easily seen on roads. It is a recipe for very dangerous road conditions mainly Tuesday morning, so make sure to take it easy, and depending on conditions and surface temperatures maybe consider travelling a little later if possible on Tuesday. By mid morning conditions should be much better, as it is March and even the sun angle will help melt ice faster than usual, though I don’t think the sun will come out and another batch of precipitation looks to move in later in the morning into the early afternoon. At this point it should be all rain, but you can never know for sure. Just make sure to keep it here for the latest coverage on this developing storm, and the next main blog update will come out tomorrow afternoon with the first stab at a Delay/Snow Day forecast for all of SW CT.