As has been outlined under the “Winter Storm Update” and on Twitter, we are following the potential for a winter storm to impact Southwestern Connecticut Tuesday into Wednesday morning. At this time, confidence is quite high that there will be accumulating snow across Southwestern Connecticut in that time frame. Confidence is also rising that this will be the last large snow-storm threat of the season, as we see a very clear warm-up following the storm, though as always there is no guarantee that a storm won’t come out of nowhere in April and disrupt the pattern. I just don’t see that at all yet. But to get to Spring, we have to deal with this one last storm threat, and it threatens to be a very strong one, potentially involving the strongest low pressure center of the entire winter season. This post will mainly outline the 3 possibilities with this storm for Southwestern Connecticut: a hit, a scrape, and a miss. I’ll break down which weather models support which solutions, which way I expect them to trend, and what the overall pattern appears to be dictating here. This blog post is a day later than I planned; mainly because I am on Spring Break in another time zone and it is hard to match up exactly when I want to release blogs with when it would be feasible for people to read them and it is hard to find the time to analyze the weather models and then report them (yesterday I spent quite a bit of time looking at data but at the end of the day didn’t have time to compile it into one large blog post). Either way, break ends tomorrow, and regular blog posts, site updates, and Twitter updates will ensue, so don’t worry; you’ll be as informed as anyone else on what the latest weather data is saying about the potential storm this coming week. Now let’s break down what it’s currently saying.
Right now, there are really 3 potential scenarios with the upcoming storm: a direct hit where the region sees a large snow storm to borderline blizzard (the strength of the low pressure center makes me confident that if we were directly impacted it, blizzard conditions would ensue), a scrape with southeastern New England seeing the worst and SWCT still getting some moderate snow and gusty winds, and a miss, where the low pressure skirts to the southeast and the region is left with just flurries and light snow as upper level energy swings through the area with no real low level connection. I’m going to outline the specific impacts in each of these three scenarios, the models that support it, and then end with a conclusion focusing on what I think is most likely, what the pattern supports, and what models will likely trend towards overnight tonight and into the next few days.
DIRECT HIT (35%): Under this scenario, a rapidly strengthening low pressure center would move near or directly over the 40/70 benchmark in the Atlantic Ocean that is the typical point a classic Nor’ Easter snow storm would move over, throwing back significant moisture and tightening the pressure gradient enough to create very gusty winds. In this scenario, we could be looking at the single largest snow event of the entire winter season, due mainly to the warmer Gulf of Mexico air and thus inflow of moisture available alongside the sheer strength of the expected low pressure center. Weather guidance has the low pressure center dropping over 40 mb before it moves through the area, meaning if it moves close enough we could see winds gusting into the 40/50/60mph range and snowfall in excess of 6-12 inches. This is not to hype the storm or scare anyone at this point, as stated there is only a 35% chance of this happening at this point, and actually and only one major weather model supports this outcome (the UKMET, whose accuracy has not always been great and which has little other model support); this is not the most likely. However, there is a very real chance of it, and March is typically known for some of the most historic storms, which is why I am keeping such a close eye on this. A slight jog west of the CMC weather model (literally 30-50 miles) would create this situation, and a few of its ensemble members show just that. The ECMWF is fairly close to this situation as well, as a shift of just 50-100 miles west of its current solution would result in a direct hit. So while only one weather model supports this (and it’s not one of the “big 3″ of the GFS, ECMWF, and CMC), it is a very real possibility. In this scenario, heaviest snow would occur overnight Tuesday night and continue into Wednesday morning, with school impacts Tuesday afternoon and Wednesday likely. This potential is why we ask you to stay tuned for the latest forecasts, because small track shifts could be the difference between this solution and the “scrape,” which is described next.
SCRAPE (50%): This is the most likely scenario, in which a very strong low pressure center (dropping below 960mb) moves far enough to our southeast that we miss the worst of the storm, with the worst centered by Cape Cod and Nantucket. Instead, the region sees gusty winds into the 30-40 mph range and light to moderate snow accumulating in the 2-5 inch range or so. In this scenario, snow would start Tuesday afternoon, though it would take until Tuesday evening for the snow to get heavy enough and for temperatures to drop enough for it to really stick. Snow then would wind down early Wednesday morning when winds pick up. School impacts would be possible Wednesday but significantly less likely than they would be in the previous scenario. This scenario is the one supported by most weather model guidance, the CMC scrapes the region most significantly, the ECMWF also has a pretty clear “scrape” scenario with widespread amounts of around 3-4 inches of snow, and the latest GFS weather model runs also show a scrape with just a couple or few inches of snow. Along with this, the thermal gradient in the ocean (the difference between very warm and very cold water, creating a path running from the southwest to the northeast) tracks just east of the 40/70 benchmark mentioned earlier, and often low pressure centers end up tracking along such areas of temperature difference. In this scenario there would still be impacts from accumulating snow, but it would certainly be nothing like the “direct hit” mentioned above with severe winds and actual heavy snow. Here, we would watch a very, very strong storm just scrape the region with the outer edge of its snow and wind, and as stated most major weather models and their ensembles support this scenario. A small shift in track, the type that would not be able to be determined until 24-48 hours before first impact, could be the difference between this scenario, a direct hit, and a miss, which is why we are going over all these scenarios and asking you to stay tuned as additional weather data streams in.
MISS (15%): Though the least likely of scenarios, there is still a potential that the storm basically misses the region entirely. Here, the storm gets shunted so far to the southeast, as some other storms have this winter season, that the region just sees some light flurries or snow showers Tuesday night with the associated upper level energy. Besides a few gusts close to 20 mph and maybe an inch or so of snow, there wouldn’t be much indication that a very strong storm was forming fairly far to our southeast. Only a few inaccurate weather models support this solution (DGEX, long range SREF members), but it remains a realistic possibility because of the trend this past month. Many storm threats we saw form only to trend southeast inside of 84 hours as they get suppressed more than expected. This is not expected nor forecasted for this storm due to upper level energy orientation I’ll touch upon in the conclusion, but because of this recent trend I figured it was prudent to include as a possibility, as honestly the way things have gone recently I would not be that surprised to see this storm slip fairly harmlessly out to sea.
CONCLUSION: So those are the three scenarios for Tuesday into Wednesday. As you can see, there is still quite a range of possibilities, and every 50-100 mile shift in track will make all the difference. The upper level energy associated with the storm moves onshore tonight, meaning that it will be better sampled by weather balloons and that hopefully weather models will begin to converge on a specific solution. As for why I think scenario 2 (scrape) is most likely, a lot has to do with all of the upper level energy players here. Most weather models have a ridge-axis at 500mb centered east of where I’d like it, which is right over Idaho. Instead, we see it over western or central Montana. Even the models and ensemble members most aggressive with the storm show that. This of course is no deal-breaker, but it leads me to believe that the storm will be slightly east of the ideal track for the heaviest snow and worse impacts for Southwestern Connecticut. Along with that, recent trends have not supported large snow storms across Southwestern Connecticut, and until I see surface observations and upper level observations supporting a strong model consensus for a large snow storm, it’s very hard to forecast one because of this. Thus, at this point, a lot of this is a waiting game to see what new data comes in and what the best way to interpret is. There are a lot of theories flying around of certain models having feedback errors or that when looking at them they “have” to trend west with this storm, but frankly I don’t entirely see it. Yes, there is a potential for a very large storm here, and that’s why I’m watching it so closely. But it is far from a lock that we get any significant impacts from this storm. There are just so many factors at play here, especially with a low pressure center deepening this quickly, that each new run of the weather models and each new release of a weather balloon could be crucial to the upcoming forecast. As always, I’ll do my best to keep you ahead of the storm and any of its potential impacts, so make sure to keep it here at swctweather.com for the latest storm information.