The 12Z GFS piles snow via 4 storms (three are pictured) across the Northeast, Midwest, and South-central U.S. The snow in the East should encourage colder weather. Consequently, the warmer East U.S. midday 12Z GFS may be too warm.

A historic warm December 2023 featuring monthly temperature departures from normal of +8F to +14F across the North-central U.S. and >4F for almost the entire northern half of the U.S. are about to fade. North Atlantic oscillation (NAO) is getting ready to shift from values >+2.0 in Mid-December to an average of about -1.5 for January 5-17, 2024. Consequently, a blocking high pressure area over Greenland forces a strong longwave trough across Central Canada to the Southwest U.S. causing a snowy/colder January regime ahead.

Based on Climate Impact Company review (so far), Graph Cast AI-generated day-10 SLP forecasts are consistently out-performing GFS and ECM. The latest important example was Graph Cast AI doubting risk of arctic air across Southern Canada and possibly into the U.S. (associated with a stratospheric warming event).

Energy markets grapple with risk of arctic air intrusion to the U.S. in 10+ days due to presence of a stratospheric warming event emerging over Eurasia over the next week or so, shifting into northwest North America in 10 days, and likely collapsing in 15 days (according to NOAA/CPC).