Some computer forecast models that meteorologists use to aid with their forecasting suggest that a winter storm will form on the east coast next week. While the overall weather pattern may become somewhat more favorable for the creation of winter storms in a month that hasn’t seen any, there is still some doubt that the storm will form as modeled on Monday.
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.
Today, the models appear to be in better agreement than they were yesterday, with both the GFS and ECMWF showing a storm system moving from the Ohio River Valley east to the Mid Atlantic coast. If such a scenario were to unfold, an area of light to moderate snow would fall across central Ohio, much of Pennsylvania, and New Jersey; north of there, only flurries would fly, while south of there would see an icy mix or just plain rain.
It is still too early to say with certainty how the system will develop and evolve, but it is worthy of watching. With both the American and European forecast models in somewhat agreement, there is more confidence in this storm system’s path than there was yesterday.
The National Weather Service office in Mount Holly, New Jersey, continues to track the potential storm. This particular office is responsible for official forecasts and winter weather watches and warnings for the area that could be impacted should a storm form: Delaware, northeastern Maryland, much of New Jersey, and eastern Pennsylvania. In a forecast discussion yesterday, they shares, “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.” They added, “It needs to be stressed that forecast confidence for this time period is still low and given how similar systems have played out recently we keep (probabilities of precipitation) at only chance. ”
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.
Snow lovers would ideally want to see a + AO / + NAO pattern develop while those anxious to get through winter fast would want to see the opposite. While winter storms can develop in either pattern, they are favored in one over the other.