Questions remain today as computer forecast models continue to call for a big storm –and perhaps 2– over the eastern United States in the coming days. It is becoming more likely than an area of low pressure will track to the U.S. east coast both on Monday/Tuesday and again on Thursday, but how the storms could evolve remain questionable.
While meteorologists have many tools at their disposal to create weather forecasts, two primary global forecast models they do use are the ECMWF from Europe and the GFS from the United States. While the models share a lot of the same initial data, they differ with how they digest that data and compute possible outcomes. One is better than the other in some scenarios, while the opposite is true in others. No model is “right” all the time.
This afternoon, these global models are in agreement that an area of low pressure will develop over the Ohio Valley on Monday and push east. Both models believe the system will slide east off the coast, with no opportunity for significant coastal re-development nor an opportunity for the system to curve up the coast. The GFS models a more robust solution than the ECMWF, which would produce a broad area of light to moderate snow over Michigan, northern Pennsylvania, northern New Jersey, and upstate New York. Because the ECMWF is less robust with this system, snow would be light at most. Both models call for marginal temperatures for snow over the southern half of Pennsylvania and New Jersey and points south, resulting in a light icy mix or simply plain rain.
Both models are now on the same page for the Thursday storm, but they too have their subtle differences there. Both forecast models suggest this storm will be far more potent than the first. But as with the first, temperature profiles will be marginal for a significant snowstorm with heavy accumulations. While there could be a wider area of snow and much more moisture to work with than the first storm, the second storm may not produce significant accumulations and could create more of a mixing scenario of snow, sleet, and plain rain. The GFS solution is colder than the ECMWF one, which suggests light to moderate snow will accumulate into Maryland, Virginia, Delaware, and points north. Because the thermal profiles aren’t as great with the ECMWF, it brings mixed precipitation up into the New York City metro area on Thursday, keeping accumulations light even on the north side of the system.
Between these systems and forecast model outputs, the best chance for significant snowfall may be confined to the higher elevations of West Virginia, western and central Maryland, and western Virginia, where the higher elevations will have more colder air to work with.
While the weather pattern is becoming more favorable for snowstorms in the Mid Atlantic and Northeast than it has been recently, it is still not ideal for blockbuster winter snowstorms. Earlier in the week, the Mount Holly, New Jersey office of the National Weather Service remarked on the weather pattern in a forecast discussion they released. “We’ll still have to watch for the potential system early next week for Monday into Tuesday. However in the big picture, there will be a strong blocking high far to our north near Baffin Island while an upper level low continues to sit and spin over Atlantic Canada. With these features as such the -AO / -NAO pattern will be continuing and this is important to note as it’s this pattern that’s helped to suppress to our south several potential storms over the past couple weeks that the models first hinted at in the longer range.” Fortunately for those eager to wrap up winter but unfortunately for fans of snow eager for a big winter storm, it doesn’t look like AO / NAO will be changing drastically anytime soon.
The -AO / -NAO pattern the National Weather Service references deals with the weather pattern over the higher latitudes. The Arctic Oscillation (AO) is a climate index of the state of the atmospheric circulation over the Arctic. It consists of a positive phase (+), featuring below average geopotential heights , which are also referred to as negative geopotential height anomalies , and a negative phase (-) in which the opposite is true. In the negative phase, the polar low pressure system, also known as the polar vortex, over the Arctic is weaker, which results in weaker upper level winds. The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south. The opposite is true when the AO is positive: the polar circulation is stronger which forces cold air and storms to remain farther north. The Arctic Oscillation often shares its phase with the North Atlantic Oscillation (NAO) and its phases directly correlate with the phases of the NAO concerning implications on weather across the U.S.. The NAO consists of two pressure centers in the North Atlantic: one is an area of low pressure typically located near Iceland, and the other an area of high pressure over the Azores. Fluctuations in the strength of these features significantly alters the alignment of the jet stream, especially over the eastern U.S., and ultimately affects temperature and precipitation patterns in this area.
More data needs to be evaluated this weekend to see how the Monday/Tuesday and Thursday storms will evolve. For now it looks like a relatively weaker early-week system will be followed by a more robust Thursday storm, but even so, between the two, odds for a heavy snowfall event appear to be low for now.