2025-2026 Winter Outlook

Winter Seasonal Forecast by Kyle Elliott

* La Niña, Negative PDO and weak polar vortex Lead to "mixed bag" Winter *

Wednesday, November 5, 2025:

The 2024-2025 winter season was chillier than the last 3 before it but still ended up as the fourth consecutive winter with below-normal snowfall at Millersville University with a seasonal total of 16.5". This winter, snow-lovers may be more satisfied by the outcome, especially during the first half of the season, but even an average amount of snow will feel like a lot after our 4-year "snow drought." One of the main factors that influence both the weather and climate in the winter are ocean sea-surface temperature (SST) anomalies, or how much above- or below-normal the surface water temperature is, in the Pacific Ocean. When SST anomalies in the equatorial Pacific are below normal, we are in a state of La Niña. When they are above normal, an El Niño is present. Last winter, La Niña conditions were declared in December, but the La Niña remained weak through the winter and faded in Spring 2025. A return of La Niña was declared in October 2025, but this winter's La Niña is also expected to be of the weak variety. In fact, La Niña may even fade during the second half of the winter with a transition back to "ENSO-neutral" conditions by February or March. As a result, you might not expect this winter to be too different from last winter, and there may indeed be some similarities during the first half of the season. However, other factors support a much snowier and colder first half of the season but transition to milder and less wintry conditions after mid-January. The atmospheric "background state" is already mirroring La Niña conditions and will likely do so for much of the upcoming winter, but the Stratospheric Polar Vortex (SPV) could throw a wrench into things from December into January. The SPV can play a major role in preventing or unleashing Arctic outbreaks across the central and eastern United States. When the SPV is strong and centered near the North Pole (2022-2023 winter season), cold air tends to remain bottled up in Arctic regions. When the SPV weakens or splits into multiple pieces, bitter cold may plunge into the eastern U.S. and/or Europe just a few weeks later. One such split occurred in February 2018 and was at least partially responsible for the cold and snowy March to follow. In fact, there were 4 significant winter storms that impacted the northeastern United States in March 2018, and Millersville received nearly 18" of snow from the March 20-21 Nor'easter. A major, Arctic outbreak also began across the Eastern States at the end of December 2017 and lasted through the first week of January 2018. This winter, odds favor a weaker SPV and one whose strength could be similar to 2017-2018 (see below). Thus, there will surely be "wild temperatures swings" this winter and, very likely, a period of severe cold in December and/or January due to high-latitude blocking and cross-polar flow (see below). How much, if any, cold and snow occurs in March is, of course, a wildcard at this distance..

The phase of the Pacific Decadal Oscillation (PDO) is yet another primary winter climate influencer. When SSTs are above normal in the interior North Pacific and below normal along the North American coast, the PDO has a negative value. The opposite is true for a positive PDO. Since 2020, the PDO has been in a highly negative, or "cool," phase and reached a record-low value in July 2025. The PDO will undoubtedly remain strongly negative through February and mirror last winter (see below). In negative PDO winters, the coldest weather (relative to normal) often occurs in the Pacific Northwest, northern Rockies, and northern Plains. By contrast, the warmest conditions are usually found in the Deep South, Southeast, and mid-Atlantic States. There may be an exception to that rule from December into early January, but I don't expect it to last during the second half of the upcoming winter. In aggregate, the coldest conditions (relative to normal) of the 2025-2026 winter season will still likely be found in the western Great Lakes region, Upper Midwest, and northern Plains.

The last factor that I'll highlight is the Madden-Julian Oscillation (MJO). The MJO, which can be thought of as an eastward-moving area of convection between the Indian and central Pacific Oceans, can be active in 8 different phases. Each phase corresponds to a specific location of this tropical convection. Which phase the MJO is active in at any given time can alter weather patterns across North America on a week-to-week basis. Based on the location of highest SST anomalies between the Indian Ocean and west-central Pacific, a meteorologist can make a reasonable guess as to which phases the MJO should be most active in during a particular winter season. This year, SSTs are highest from the Bay of Bengal to areas north/east of Australia. Meteorologists refer to these regions as the "Maritime Continent" and "Western Pacific," and high SST anomalies in these regions promote MJO activity in phases 3-7. These are generally considered "warm phases" for the eastern U.S. during a La Niña winter, but phases 6-7, in particular, can actually produce the opposite effect (i.e. colder and more wintry periods) across the eastern U.S. in December and January. Given current MJO activity in Phase 5 and slow progression toward phases 6-7, I expect the convection to finally reach those colder phases by early-to-mid December. Thus, the progression and intensity of MJO activity will likely play a significant role in our weather during this year's holiday season and increase the odds of a "White Christmas" and colder-than-normal December.

The recipe I use to create a winter seasonal forecast is actually quite simple. I look at the distribution of temperature and precipitation patterns across the U.S. in past winters with similar conditions to those I expect in the upcoming winter. These are called "analog years," and they're a vital part of seasonal forecasting. In weak La Niña winters with a highly-negative PDO and weak Polar Vortex (what I'm expecting this year), there tends to be an active, Pacific storm track and lack of big, East Coast snowstorms, or Nor'easters. Most storm systems should follow, or "come out of," the Jet Stream's northern branch this winter, so they'll often track to our north and west and be unable to tap into rich, Gulf of Mexico moisture. As a result, I expect frequent light precipitation events this winter with "moisture-starved systems" being the norm. We will likely experience many "all-rain events" and a few "changeover storms" where precipitation starts as snow but quickly turns over to ice or rain. The exception to this could be from mid-December through early-January. Despite overall drier-than-normal conditions during this time, a persistent, 2-4-week period of "sustained cold" should support a few "all-snow events" and at least one moderate snowfall of 6-10" across northern MD and southeastern PA. Along these lines, I can't rule out a significant ice storm, as well, between Dec. 15 and Jan. 15. However, any "big storms" will tend to cut into the Great Lakes region or up the spine of the Appalachians, placing the Lower Susquehanna Valley on the "warm side" of these systems. There should be a predominance of mild air across the eastern half of the nation from mid-January into late-February, so the "worst of winter" in terms of cold and snow should occur early on and be centered around the holidays (see below). Thus, temperatures in December should be at least 1-3°F below normal, but the early-season cold should be offset by a mild February with temperatures at least 2-4°F above average. Aggregate temperatures in January may end up "near normal" due to the contrast between the first and second halves of the month.

In aggregate, I am expecting 20-30" of snow this season in Lancaster County and most of the Lower Susquehanna Valley with a below-normal chance of a major, 12"+ snowstorm. Total precipitation (rain, sleet, ice, and snow) will likely be near- to slightly below-normal with aggregate temperatures around average (0 to +2°F) from December-February. Get ready for a wild ride this winter, especially in terms of temperatures.. -- Elliott