Weather forecasting is a science and an art. It is the careful balance of hundreds of natural physics calculations programmed into super computer-based models that output visual/graphical predictions about weather. Meteorologists interpret these different outputs and, using their own knowledge, judgement on the different model outputs, and possibly past analogous weather/storms, deliver a forecast.
This storm was quite interesting because of how it was handled by these computer-based forecast models. When making weather predictions more than a day in advance, meteorologists often look at global numerical weather prediction models. As their name suggests, global models attempt to reflect weather conditions worldwide based on the “global” interactions between the atmosphere, land, ocean. There are over 30 different global models but the two that are most cited and often most utilized in the United States are the ECMWF Model (aka the “Euro”) and the GFS (aka the “American”). Both of these models have the ability to “predict” weather up to just over two weeks in advance but are not very accurate beyond a 5 day period. The Euro, historically, has been considered the overall most accurate model; it runs using more powerful super computers, better accounts for the interaction between the ocean and the atmosphere, and has had more funding as it is supported by 23 European nations. In order to improve its accuracy, the GFS, which is run by NOAA, went through a major upgrade in 2019 and, today, is considered to be the more accurate model when it comes to forecasting hurricanes. Regarding general forecast predictions, however, the Euro is overall considered more accurate.
This winter, the Euro has struggled. It did not do the best of jobs predicting our late January Nor’easter, which ended up being the 8th largest snowstorm on record for the Boston area, and forecast a direct hit from ocean storm a few weeks ago that ended up being a miss. This storm may be a win for the GFS and another blunder for the Euro.
The GFS predicted this Nor’easter would be a direct hit early this past week. In fact, it was alone on an island with this prediction; all of the other major global models saw this storm as a miss. This includes the Euro.
The models differed in how the jet stream was set up. The Euro saw the jet stream over the east coast as being less steep, resulting in a less powerful storm that went out to sea after exiting off the Carolina coast. The GFS foresaw a steeper, sharper jet stream, allowing for the storm to ride up the east coast and rapidly intensify in the process.
By Thursday, the Euro started to move the storm track further west and, by Friday, was almost in line with the GFS.
This storm is a classic Miller A Nor’easter, a rapidly intensifying coastal storm that originates as a low pressure system near the Gulf of Mexico. These storms hit the mid-Atlantic and southern New England the hardest. For comparison, our late January Nor’easter was a Miller B storm, which originate from low pressure systems traveling across the middle of the country and forming a coastal storm off the coast of the Carolinas. These storms often deliver heavy precipitation but generally are not as strong as Miller A storms.
This storm is predicted to intensify rapidly and undergo bombogenesis. Also known as “bomb cyclones,” the pressure center of these “amped up” Nor’easters drops 24 millibars in 24 hours. This is a defining feature of strong Nor’easters caused by the clash of warm, tropical moisture from the Gulf Stream clashing with Arctic air being drawn down from Canada. The clashing airmasses act as jet fuel for Nor’easters, deepening the storms, generating intense winds, and enhancing snowfall rates.
Another factor at play which may help make this a “historic” Nor’easter is where it moves once it reaches our latitude. The “40-70 Benchmark” is often mentioned by forecasters when talking about snowfall totals and wind speeds. A Nor’easter passing over 40 degrees North latitude 70 degrees West longitude is far enough away to prevent too much warm ocean air from being pushed towards the Massachusetts while simultaneously being close enough to deliver very heavy precipitation. This generally means the heaviest snowfall will be concentrated towards Eastern Massachusetts without the threat of a rain-snow line in play.
What does this translate to for us? It is looking like our first true blizzard since 2022 and possibly a top 10 winter storm for eastern Massachusetts. Early estimates from the mesoclimate models, short-range, very localized weather models that can be used a day in advance of storms, suggest some areas of eastern Massachusetts could be looking at over 2 feet of snow. We will see how this plays out as the storm wraps up early Tuesday morning.