Coldest Anomalies of U.S. Meteorological Winter 2024-25 in U.S. Just Ending?
12/08/2024, 12:35 pm EST
Focus on Today’s Northeast U.S. Squall Line
12/11/2024, 8:50 am EST
Highlight: Hot forecasts; PV pattern may emerge early January.
Chart of the day: CFS V2/ECM Week-4 Forecast Skill Scores.
Discussion: Since late October, reasonable skill scores for week-4 forecasts by ECM have decelerated to near zero while choppy CFS V2 skill scores from late warm season have collapsed to below zero. Recent skill scores collapsed due to the un-forecast cold wave to start December in the East.
Week-2 Ahead Forecast valid December 15-21, 2024: Mild pattern; Renegade cold air masses southeastward from Western Canada?
Discussion: ECM projects a warm upper ridge in the West as compensation for a vigorous upstream Gulf of Alaska low pressure. Most of the U.S. is mild although a cold air source region remains over west/northwest Canada. Monitoring for renegade “sneaky cold” air masses from Western Canada toward the Northeast Corridor.
Week-3 Ahead Forecast valid December 22-28, 2024: Very warm forecast.
Discussion: ECM is prohibitively warm and warmer than the previous forecast. The stratosphere is cold across North America and causal to the anomalous warmth. Canadian warmth is likely overdone due to deep snow cover.
Week-4 Ahead Forecast valid December 29, 2024-January 4, 2025: Colder than indicated in the Northeast.
Discussion: Upper trough appears in Quebec and that zone (into New England) is likely colder than forecast by ECM.
Week-5 Ahead Forecast valid January 5-11, 2025: Possible polar vortex pattern.
Discussion: ECM indicates a polar vortex just south of James Bay. The colder forecasts for the extended range are unusual for this model. The cold is likely wider and more intense than indicated.