La Niña and Potential Stratospheric Warming Signal Potential for Extreme 2025-2026 Winter Weather

Forecasters are projecting a potentially significant winter season across the United States for the 2025-2026 period, driven by the anticipated persistence of the La Niña climate pattern alongside the possibility of a Sudden Stratospheric Warming (SSW) event influencing the polar vortex.

The National Weather Service indicates that La Niña conditions are favored to continue from December 2025 through February 2026, a phase that typically directs the polar jet stream southward, channeling frigid Arctic air into lower latitudes. NOAA’s Climate Prediction Center confirmed a 71% probability that a weak La Niña will develop between October and December 2025, with a transition back to ENSO-neutral conditions projected by March 2026. While a weak La Niña often correlates with near-to-slightly-above-normal temperatures and precipitation for areas like Washington, D.C., and Baltimore historically, the concurrent risk of an SSW event introduces considerable uncertainty.

A Sudden Stratospheric Warming is a rapid thermal event in the stratosphere, sometimes involving a temperature increase of 30 to 50°C over a few days, triggered by the upward propagation of atmospheric waves, such as Rossby waves. When these waves disrupt the stratospheric polar vortex—a region of high-speed winds high above the surface—they can weaken its westerly winds, potentially causing the vortex to split or shift entirely off the pole. This displacement allows frigid air to spill southward into the mid-latitudes, a mechanism that can unleash intense cold and substantial snowfall.

The historical precedent of December 2000 illustrates the potential severity of such a disruption; that month was the second coldest December in 106 years for the Midwest, with Illinois recording its coldest December on record. That period featured an active storm track and a significant nor'easter that dropped up to 30 inches of snow in areas west of New York City between December 27 and 31, 2000. The main uncertainty with any SSW event remains the exact trajectory of the displaced cold air across the Northern Hemisphere.

Current outlooks suggest colder conditions for the Central and Eastern United States, with the Great Lakes and Northern States facing higher chances for heavy snow, while the South is generally expected to remain warmer and drier under the weak La Niña pattern. The convergence of these atmospheric factors—a persistent, albeit weak, La Niña and the potential for stratospheric disruption—requires close monitoring as the season progresses, as these interactions fundamentally govern winter climate variability in the mid-latitudes.