The negative phase North Atlantic oscillation forecast continues and inevitably drives colder changes in the East U.S. Helping to increase East U.S. cold risk is a southern and sustained shift of snow cover across the Northeast States.

The Climate Impact Company month 1-4 climate outlook for South America valid for January through April is updated. The constructed analog forecast is based primarily on lingering La Nina climate through Q1/2026 coupled with unusually warm SSTA off the West Coast. A trend toward El Nino could initiate as early as April.

As a precursor to the developing “atmospheric river” pattern, widespread high wind covers the Northwest U.S. to North-central States for WED/THU. Highest wind is downslope the Northern Continental Divide into the northwest Great Plains and across mountain areas of the Northwest States. Mountain areas will observe blizzard conditions already in effect for the Washington Cascades.

An important climate diagnostic, missing since last April, has returned this month: Multivariate ENSO index (MEI). The MEI identifies the response of the atmosphere (30S to 30N) to the Pacific equatorial sea surface temperature anomaly (SSTA) regime. Note that the conventional climate diagnostic to identify ENSO phase, the Nino34 SSTA, only recently shifted to La Nina. A La Nina regime is indicated by MEI all but APR and MAY of the past 12 months.