This will be the first of many updates this afternoon for the upcoming snow storm. They all will likely have different focuses, some focusing specifically on school impacts, other on snow accumulations, and even others on short range model/surface trends that could drastically affect the forecast. I’m going to start this blog with a brief disclaimer basically stating that while confidence is growing in the storm, the extreme cold present in the second half and behind this storm makes forecasting accumulations very difficult, which is why ranges will remain so big across such small areas. I’m doing my best to narrow it all down, but small variations in microclimates of just a few miles could make differences in just how fluffy the snow is. With that, I’ll outline the blog; I’m going to start breaking down a small adjustment in accumulations downward that I’m making and I’m going to explain it. I’ll then tie in timing and accumulations to explain why I am forecasting schools to close on Friday. I’ll end with what I think could go wrong with the forecast at this time, and again reference the extreme cold coming in behind the storm.
To begin, I’m slightly adjusting accumulations for the region. Coastal areas are being dropped two inches, and inland areas are being dropped an inch. This results in a range of 6-12 inches of snow expected for anyone south of the Merritt Parkway and 7-13 inches north of the Merritt Parkway. As I’ve explained before, I do not like to adjust snowfall forecasts unless I am fairly certain that it is inaccurate, but recent trends show to me that especially coastal areas may not hit the 8 inch amount that I had expected them to before. This does NOT mean that they won’t, in fact I still think it is likely that the entire region ends up somewhere in the 8-10 inch range of snow. But because of the complexity of the storm I’ve extended the range on each side of that to 6-12 inches for the area. Inland, surface temperatures will be slightly colder meaning there could be even better ratios from the start of the more moderate precipitation this evening, thus I bumped up amounts an inch. Some short range guidance also shows isentropic lift could be enhanced at the onset of precipitation by additional elevation, possibly enough to boost accumulations inland by an inch or so. Recent model guidance, while not perfectly supported by surface observations, is close enough that I feel confident in forecast a general half inch to .65 inches of liquid across the area. I’ve been calling for snowfall ratios of around 13:1 or 14:1 at the coast and around 15:1 or maybe up to 16:1 inland. Again, when the air is colder snow forms with more air and is fluffier, thus it stacks quicker and it takes less moisture to reach the same accumulation of snow on the ground. When taking these liquid amounts and applying the ratios, the coast sees anywhere from 6.5 inches to around 9 inches and inland areas see anywhere from 7.5 to 10 or so inches. Again, the ranges are more broad because ratios are certainly not definite, and there is still a chance that the 500mb trough of low pressure dictating this pattern turns neutral a little sooner, strengthening the low pressure at the surface closest to us quicker and enhancing precipitation. The most recent Rapid Update Cycle short range model showed more of this and has been trending in that direction, which is what I continue to keep an eye on.
Some models also try and apply ratios themselves, like the GFS for example, which has .6 inches of liquid for the area but around 10 inches of snow on the latest run. I left this section to go in depth about short range models, but I don’t feel the need, especially as this forecast is based off of as much surface observations as it is models. With surface temperatures in the low 20s to teens in many areas and temperatures already beginning to drop into the evening, it makes sense that ratios will be very high, hence snowfall totals that are much higher than the liquid equivalents. Even a little more enhanced snowfall could give someone in Southwestern Connecticut a foot of fluffy snow. And the RUC model mentioned earlier shows that in areas snowfall rates could approach an inch per hour. The craziest part that doesn’t even include ratios! Meaning snowfall rates of over an inch per hour are quite possible, and in many cases could be likely this evening. I’ll be tracking bands on radar and reporting both on here and on Twitter.
SCHOOL and TIMING: So now I want to go in again and break down both my school forecast and the timing forecasts, which really go hand in hand. As expected, I am not seeing any reports across SWCT of more than half an inch of snow from this morning, and radar shows it will be at least a couple more hours before even light snow showers may enter the region. This is why I was so critical of numerous districts across Southwestern Connecticut closing early today; there just was no reason to as the main precipitation shield won’t even get close until around 6 PM and I don’t see road conditions getting dangerous and snow getting really steady until 7 PM or maybe even 8 PM across eastern zones. However, by 8 PM I expect road conditions will be going downhill very rapidly as all snow sticks instantly due to very low surface temperatures, even on most treated roads. Heaviest snow bands look to occur between 11 PM and 3 or 4 AM. Snow looks to continue through 5, 6, and 7 AM before it eventually winds down between 8 and 10 AM. What does this mean for schools? Well, for one thing it means that I see almost no scenario in which schools open on time. You would be hard pressed to find a solution where snow ends before 7 AM and roads are safe to drive on. That leaves two options, either a delay or a closure, for superintendents to pick between. As I’ve shown, some models have up to another half inch to inch of snow falling after 7 AM, and a few have snow lasting all the way until 10 AM. After anywhere from 6-13 inches of snow with winds still gusting into the 20 mph range blowing a fine, powdery snow all around and temperatures in the single digits through at least 8 or 9 AM, I find it unlikely for schools to open on Friday. In fact, conditions are going to be so severe with winds, cold, and blowing snow, along with the accumulating forecast to fall tonight, that many districts may simply kill the suspense and announce this evening that they are closing for the day tomorrow. With Winter Storm Warnings up and severe cold coming, it could very well be the right call. Other districts may decide to wait it out until tomorrow morning and see what conditions are. Due to numerous snow days, a few districts may try and clear roads in time for a delay. The only reason I have that as high as I do at 35% is because there is a chance snow ends by around 8 AM and a few districts may be able to sneak by with just delays IF and ONLY IF the extreme low range of forecasted snow is met. In any other scenario I see schools needing to close as roads will just be too dangerous tomorrow morning. Because I do not expect the extreme low range of my forecast to verify, throughout the day I expect the chance of snow days to rise and those of delays to fall. Regardless, snow days are forecasted for ALL SCHOOLS in Southwestern Connecticut, and this is a forecast that I believe I will be sticking with all day today and all night tonight. The percentage chance is only going to go up with future updates unless something major changes.
I briefly touched upon the cold and wind, but I’d like to go into a little bit more detail. Temperatures will be in the teens within a few hours if they are not already wherever you are in Southwestern Connecticut. Temperatures are colder than forecasted, and that could boost ratios even further. Far northern Fairfield County could be approaching the single digits before 11 AM or midnight, when the heaviest snow is moving into the region. Then by 1 AM almost all of inland Southwestern Connecticut will be in the single digits with low teens at the coast, and then by 3 or 4 AM all of Southwestern Connecticut will be in the single digits except maybe extreme coastal areas south of Interstate 95. Temperatures will be very slow to rise Friday morning due to the fresh snow cover, brisk north winds, and cloud cover. By 10 AM most of the region is STILL likely to be in the single digits with wind chills either around or below 0. Schools may be delaying simply due to cold weather if there wasn’t 6-13 inches of snow having fallen the night before. Throw in wind gusts to 35 mph between 1 and 4 AM and you will see some wicked cold wind chills approaching maybe 10 or more below 0. Even between 7 AM and 10 AM sustained winds will be around 10-15 mph with gusts into the 20 mph range keeping wind chills subzero throughout most of the day tomorrow, especially before noon. So expect severe conditions even after the snow stops.
CONCLUSION: Between the heavy snow tonight, the extreme cold continuing into tomorrow, and the gusty winds blowing snow around tomorrow morning, I am forecast a SNOW DAY for all of Southwestern Connecticut. There remains an outside chance of delays if conditions are not as severe, but I’m quite confident in calling a snow day and percentages are likely to go up. Snowfall amounts have been slightly dropped as models came into agreement on the amount of liquid that will be available in this storm, but it was only a small adjustment, and it is quite possible that most totals end up in the forecasted range I had earlier as well. For the sake of information, I wanted the most accurate range that is supported both by my thoughts and by surface observations and weather models, and so we have 6-12 inches of snow forecasted at the coast and 7-13 inches forecasted inland. Make sure to keep it here as the storm develops and moves closer throughout the day. I’ll be having continuous blog posts and tweets to keep you ahead of the storm.