There is growing confidence that a possible snowstorm will affect the Northeast U.S. during the middle of next week, as the ingredients needed for one to occur are beginning to consistently show up on the models. It seems this winter has been relentless with the constant cold and frequent snowfalls. This type of pattern just does not want to let go — not yet, at least.
Plenty of clouds have been the rule for today, which have helped to keep temperatures in the 30s. A storm system to our south is slowly moving northward, but will not interact with the jet stream to the north. This will keep the storm system out to sea. The lower pressures from the jet stream to the north, as well as the lower pressures out to sea, will help to create a relative wedge of higher pressures between them, which is another reason why the storm will ultimately miss us, as higher pressures create sinking air, thus a lack of lift. There is the outside chance of a few very light sleet pellets or drizzle in coastal sections, but we’re definitely leaning against that, and even if that were to occur, it would not disrupt any travel.
As the storm pulls away throughout the night, clouds will gradually diminish, as winds turn to the north. The initial cloud cover will prevent temperatures from dropping much below freezing, however.
Moving to tomorrow, a cold front will be developing in the Great Lakes via the northern jet stream, and moving eastward throughout tomorrow. This will help to the winds to turn more westerly as opposed to due northerly. This, combined with the previous subsidence left from the departing storm system will lead to sunny skies for tomorrow and a potentially warm day.
Today’s high-resolution NAM run shows 850mb temperatures around +3C at 1:00pm tomorrow afternoon, which support high temperatures in the 50s, given enough sunshine and mixing. (PSU E-Wall)
Temperatures aloft have slowly warmed due to more ridging building in between the low pressure offshore, and the low pressure in the northern stream. As sunshine comes out in full-force tomorrow, the relatively strong sun angle, combined with the fact that winds will be turning more to the west should lead to temperatures warmer than forecast by most other outlets. 850mb temperatures will be around +3C at 1:00pm and the flow will be pretty strong out of the west, as shown in the map above. This leads to downsloping off the Appalachian Mountains, which warms and compresses the air. The only thing that would prevent temperatures from exceeding 50 degrees is if the atmosphere takes a bit too long to become truly mixed, because of the previous higher pressures preventing much atmospheric turbulence. However, due to the winds and strong sun angles, we believe the atmosphere will become mixed by around noon or 1:00pm. This would help to translate the warm temperatures aloft to the surface. With a strong sun angle, you can often add 10 to 12C to the 850mb temperatures to the surface.
Interestingly enough, BUFKIT soundings show the atmosphere becoming fully mixed at 3:00pm, but temperatures aloft have cooled a bit by then, due to the approaching cold front — when a cold front approaches, the temperatures aloft fall faster than they do at the surface, due to stronger winds aloft. This is why most high temperature forecasts are only in the 40s for tomorrow. But just move the mixing up a couple of hours, and we are easily in the 50s for tomorrow, which seems to make sense given the strong sunshine. Thus, we feel that temperatures should reach the low 50s tomorrow, which will feel quite pleasant due to how cold it had been previously. Average temperatures this time of year are actually in the mid to upper 40s, so tomorrow’s warmth will not be unseasonable.
The cold front moves through on Saturday night, which will lead to Sunday having trouble getting out of the 30s, as well as some scattered snow showers on late Saturday night/early Sunday morning. Then, attention shifts towards Wednesday, as another potential storm begins to form.
After getting bombarded by storm after storm this winter, it appears that the pattern for the next several days will finally relax, as no major storm systems will be on the horizon. There is a storm system developing in the Southeast states, but it will be become disconnected with the jet stream. This means that there will be no northern stream piece of energy to phase with it and bring it up the coast, thus the storm will stay to our south for Thursday and Friday.
Another inconvenience we have to deal with, however, is the cold temperatures for tonight and tomorrow. Today saw decent moderation, as the previously cold high pressure system slid out to sea, and allowed our flow to become more maritime in nature. But as this high pressure system moves out, another strong one will be moving in tonight and tomorrow. A 1040mb high pressure system will pass overhead, and allow for our winds to turn due northerly tonight, which is the most efficient way to generate cold into our area, since that wind direction allows for no downsloping, nor moderation.
While this run may be slightly overdone in cold, the 4KM NAM shows bitterly cold temperatures being advected into the region tonight. (PSU E Wall)
The wind direction coming purely from the north via a 1040mb high (strong cold air source) leads to forecast very cold temperatures tonight — dropping into the mid teens in the City, and perhaps upper single digits to around 10 in northern and northwestern suburbs. There won’t be any true radiational cooling, however, due to the strong winds, so temperatures may tend to run a bit more uniform tonight.
Some data indicates the initial slight chance for a snow shower tonight as temperatures aloft drop more than they do at the surface initially, creating some instability. However, we feel that the strong high pressure system will create enough subsidence to limit any snow shower activity, except for areas further north and west with a bit more elevation/orographic lifting.
Although our forecasts were lower in snow totals for the NYC area than some other outlets at the time they were issued, we still feel like we could have done a better job. Apologies go out for a missed forecast. But, as scientists, we always try to do our best to analyze what went wrong, and how this could help improve forecasting down the road. We did have lots of ideas and gave some warning about the uncertainties with the storm and the beginnings of the south trend in this article, as well as giving a brief explanation of why the storm was trending south in this article, but we did not reflect these thoughts strongly enough in our forecast maps. We will begin dissecting the several aspects that went into the forecasts and how everything changed.
1) Previous computer model forecasts not only consistently showed a major snowstorm, but they made sense given the general pattern they were forecasting.
Sometimes when computer models forecast a snowstorm, they may come up with what we call a “pulling a rabbit out of a hat” solution, where lots of features luckily and coincidentally fall into place, in a general pattern that does not necessarily support these features falling into place. That does not mean snowstorms are impossible in those scenarios, but they are less likely.
This time around, however, there were many favorable features, at least initially. A relatively potent southern stream shortwave ejecting into an Arctic airmass, and pieces of energy from the northern stream of the jet stream were diving down and interacting with the southern stream, helping to pull more moisture northward.
The 00z Friday (2/28) European Model run showed quite the favorable pattern for a major snowfall for New York City. But small changes with the handling of the Polar Vortex and associated energy led to exponential shifts in the eventual track. Image credit goes to the WSI Model Lab.