With the start of Meteorological Winter days away on December 1, global forecast models are indicating for the first time this season a potential winter storm threat for portions of the Northeast during the first full week of the new month. But don’t stock-up on milk, bread, and toilet paper just yet; the models may not be projecting things accurately yet.
December 1 marks the arrival of the 2025-2026 Meteorological Winter Season. Meteorological winter is a three month period that runs through to the end of February. In the Northern Hemisphere, it is the coldest three month period of the year. Meteorological Winter is different from Astronomical Winter, which is based on when the sun reaches the most southern point on the globe, the Tropic of Capricorn. If you are right on the Tropic of Capricorn at 12 noon on the first day of Astronomical Winter, the sun will be directly overhead. This year, that date is Friday, December 21. While winter is starting in the Northern Hemisphere, summer begins in the Southern Hemisphere. The word “winter” comes from the Germanic “wintar” which in turn is derived from the root wed meaning ‘wet’ or water’, and so signifying a wet season. In Anglo-Saxon cultures, years were counted by the winters, so a person could be said to be “2 winters old”.
The GFS and ECMWF are among many computer models meteorologists use to assist in weather forecasting. 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. Beyond the ECMWF and GFS models, there are numerous other models from other countries, other academic institutions, and private industry that are also considered when making a forecast.
For the last several runs, forecast models like the GFS and ECWM have indicated that a winter storm will take shape in the northeast in early December. Specifically, they’re suggesting the most wintry impacts to the Northeast on December 2-3. Of the global models, the GFS is the most robust with its solution, depicting a developing low pressure system off the DelMarVa coastline that helps bring accumulating snow to portions of the northern Mid Atlantic and southeastern New England. Yesterday the ECWMF also had a robust solution but it brought the system far into the northeast which would translate into rain for places like Stamford, New York, and Philadelphia. But today, the ECMWF has shifted the storm far south and east, keeping those same cities cold but dry. Other global forecast models offering differing projections too, with some bringing a significant snowfall to the I-95 corridor, others produce just rain, and some even suggest it’ll be mainly dry.
Weather forecast models become unreliable many days in the future because the atmosphere is a chaotic system. Minute differences in the initial data used to start a forecast get amplified over time, a principle known as the “butterfly effect,” leading to vastly different outcomes. A forecast for a 10-day period or longer is only correct about half the time, compared to a five-day forecast, which is about 90% accurate. Because this potential storm system is just outside of a 5-day forecast window, there isn’t a high degree of confidence in how the storm will evolve.
As the Thanksgiving holiday weekend wraps up and more data is digested by computer forecast models and reviewed by trained meteorologists, more clarity will come to focus with the forecast to see how exactly this storm system will evolve. For now, people in the northeast should be aware that some forecast guidance is calling for the possibility of a winter storm, but it’s too soon to say with a high degree of certainty where it’ll be and how impactful it will be.
