The 2025-26 cold season is barely underway and already two dramatic weather regimes are identified: 1.) The just-ending arctic outbreak across the East U.S. and 2.) The evolving excessive precipitation event for the West Coast lasting the remainder of December and into January.

The arctic oscillation (AO) which identifies the location of the polar vortex indicates a change to positive phase the next 1-2 weeks as the recent frigid Canadian polar vortex shifts poleward. The shift toward the North Pole allows milder Pacific maritime influence to warm the U.S. pattern. The extended-range AO forecast suggests the positive phase may continue well into January. However, there are caveats.

November and meteorological autumn (2025) were exceptionally warm, ranking 4th and 3rd warmest respectively. Oregon and the Interior West plus Texas observed record warmth during the period.

The general lack of precipitation of the past month (except Indonesia) may be a contributor to a wet bias of operational and AI 15-day forecasts for North and South America plus Europe. The ECM ENS is characteristic of all operational forecast models producing a wet forecast bias in 15-day outlooks for the past 30 days for the Americas. AI models have a similar common problem as demonstrated by AIFS ENS for Europe.