Climate signals forecasts identify provide clues as to where the weather pattern is heading after mid-December. The West Pacific oscillation (WPO) and Pacific North America (PNA) index is negative after mid-December supporting a shift and expansion of the cold pattern over western North America. Negative East Pacific oscillation (-EPO) spikes in one week as another “polar vortex” cold outbreak strikes the U.S. The North Atlantic oscillation (NAO) aggressively shifts to positive phase during the medium range supporting an eastern North America warm-up and validating the -WPO/-PNA colder support in the West. The question is whether -NAO warmth can eat away at the snow cover validating very warm 11-15-day forecasts by ECM.

Snow cover extends across much of the northern half of the U.S. east of the Continental Divide today retreating slightly in the East during the next 2 weeks while building dramatically over Western Canada to the North-central U.S. where arctic air generation is likely.

Last week, the NINO SSTA regions warmed including the Nino 4 (near the Dateline) and Nino12 (northwest coast of South America) where sea surface temperature anomalies (SSTA) shifted to neutral phase. The Nino34 SSTA barely remains within the La Nina threshold. The warming is likely due to weakening trade winds slowing the upwelling of cool water process.

An exceptionally cold start to meteorological winter 2025-26 in the East with a frigid 15-day forecast for New England/New York including 2 cold spikes (Dec. 5 and Dec. 8-9) and a long stretch of cold for the PJM Sector although some moderation in the extended range.