I wanted to pass along a brief update on what I’m seeing with the storm, why it is trending south, and why I think that the southern trend is done and the models are picking what may be close to a final scenario. This won’t be as comprehensive as the most detailed updates, but it will be fairly detailed as there are many updates to cover. As always, an abbreviated version can be found under “Winter Storm Update” on the right hand side of the website. I’ll break this down briefly into timing/precipitation type, accumulations, and school impacts, with some more technical bits woven in between them all. Here we go.
TIMING/PTYPE: So, overnight most weather models trended towards the suppression that the GFS showed yesterday. While not entirely expected, this is not a huge surprise. However, the going forecast still believes the GFS run the forecast yesterday tried to discredit was overdone. Accumulating snow is still coming to the region. First things first, it no longer looks like rain/sleet will be an issue. There is a chance some freezing rain briefly mixes in at precipitation onset or Sunday evening when there is a single push of warm air aloft but even that looks very unlikely. I expect the entire storm to be all snow for Southwestern Connecticut. In terms of timing, tomorrow morning or early afternoon a quick round of snow moves through accumulating maybe a half inch to an inch. Most short range models have picked up on this, and then we get a break. After that, things begin to get more complicated still. Most models have steady snow moving through by tomorrow evening into the overnight hours. There is general agreement in steady snow between 9 PM and 1 AM across all of Southwestern Connecticut, and the majority of accumulations will happen then most likely. Now is where models diverge: some, such as the SREFs and the GGEM/RGEM to some degree (and even the GFS now!) keep at least light snow going until 7 AM and a few even as late as 11AM/12PM on Monday. Other models, such as the NAM, show snow ending by 9 or 10 PM on Monday, but has the burst of snow being heavier before then to even out accumulations. My tendency is to believe that snow lasts longer than the NAM shows, the frontal boundary won’t press THAT far south, and I think light snow lingers into Monday morning. However, by Monday afternoon snow has entirely moved out of the area; all models agree on that. Any impacts to schools and businesses will thus be early on Monday, as snow will already likely be winding down by Monday morning.
ACCUMULATIONS: The going forecast has been updated, now calling for 2-4 inches of snow inland 3-6 inches of snow at the coast. Model QPF varies from .2-.5 inches or so inland and .25-.7+ at the coast. Most weather models are clustered in the lower range of moisture though, thus the slightly lower ranges. My totals are in line currently with the National Weather Service, and I think we are seeing eye-to-eye on this storm regarding accumulations. It’s a very tricky forecast because if most modeling is correct, SWCT just gets scraped by snow into early Monday morning, hence why the coast has higher totals than inland. Any variation thus could bring the coast either into heavier snow for a longer period or into lighter snow for a shorter period of time, and every couple miles will determine the exact snowfall gradient. Thus models have to be watched closely, but I actually am fairly confident in the ranges I am calling for right now, and there is about a 25% chance they will need to be raised, and a 20% chance they will need to be lowered. Another potential wrench in the forecast is snowfall ratios, which as I have stated before will start very low but will rise throughout the storm. By the end, snow will be fluffier and will accumulate quickly, but the big unknown is how much if any moisture there is over SWCT at that time. If none, we end up being in the lower end of forecasted snow that will fall through midnight Monday. To get into the higher ranges of the forecast, we need light, high ratio, fluffy snow to continue falling into Monday morning. The longer it lasts, the higher accumulations, which is why I think 6 inches isn’t unrealistic for someone in SWCT, though it is fairly unlikely. My best guess is that inland areas center around 2.5-3 inches of snow, and the coast centers around 4 inches, but again there is high variability here, as evident in a NWS location forecast calling for anywhere from 3-7 inches of snow. I hope over the next 36 hours to be able to really hone in the forecast.
SCHOOL IMPACTS: This makes for a very hard school impact forecast. If the higher ends of the forecast range are realized, then schools will likely have to close Monday as snow will continue into the morning. If the lower ranges are realized, or the snow ends very early Monday night, schools may be able to open on time. Any scenario in between would result in school delays. All three of these options are on the table, though I think coastal districts have slightly higher chances of school impacts on Monday because the snow is expected to last longer in those areas. Percentages will be up tomorrow, and this will be a very close call so make sure to keep checking back on here and on Twitter for updates regarding Monday school impacts as very small tweaks in the forecast will likely make the entire difference between school districts being able to open, delay, or close. It’s just too early for me to make any definite calls here without knowing the exact details, but I do think that there is a significant chance that numerous districts will be impacted in some way by this storm.
CONCLUSION: Overall, we are looking at 2-4 inches of snow inland and 3-6 inches at the coast (dividing line of the Merritt Parkway) that will fall between Sunday late morning and Monday morning. A brief burst of snow late tomorrow morning will be followed by a lull and then steadier snow tomorrow late afternoon and evening into the overnight hours, with the heaviest snow likely in the late evening or early overnight hours. Snow may then linger, staying light, into Monday morning, potentially delaying or closing schools depending on exact timing and accumulations. As I have said, this is a very difficult forecast, both in terms of accumulations and school impacts (this seems to be a common trend this winter) so I’ll be updating on Twitter throughout the day and we will have continuous coverage tomorrow into Monday. Make sure to stay tuned for the latest potential winter weather impacts across Southwestern Connecticut.