The Climate Impact Company month 1-4 outlook valid DEC-25 through MAR-26 is updated. The forecast is trending colder. The North-central U.S. cold anomalies expand, and the Northeast/Mid-Atlantic are adjusted cooler to near normal. Cold outbreaks cover the suddenly snowbound Northern U.S. in December, a January cold surge into the East U.S., and Western Canada to North-central U.S. cold (possibly reaching Texas) in February.

The North America snow cover lagged below normal during mid-autumn thanks to a warm Canadian climate while advection snows across the open water north of Eurasia during October allowed snow cover to build above normal during mid-autumn for the 15th straight year.

Generally, sudden stratospheric warming (SSW) events capable of producing arctic outbreaks are considered more likely during easterly phase of the quasi-biennial oscillation (-QBO). Past winter seasons when -QBO was developing in November, similar with 2025, and peaking during the winter season, similar with winter 2025-26 expectation, are identified (since 1979).

STRIKING is the weakening of anomalous cool waters in the equatorial East Pacific during October. Note that the cool anomalies present in the subsurface equatorial Pacific are about 30% of the strength present this past January which supported a moderate strength La Nina episode. Unless upper ocean heat across the equatorial Pacific to the east of the Dateline cools dramatically over the next few weeks, the current La Nina will end.