Why the frigid 11-15-day forecast won’t happen. Snowstorm update.
Fig. 1-2: The 12Z mega-cluster ensemble “most likely” (left) and second-most likely 11-15-day temperature anomaly forecast for North America.
Discussion: See any difference? The 11-15-day temperature anomaly forecast is warm into the North-central U.S. according to the “most likely” scenario for forecast days 11-15 (Fig. 1). Forecast confidence is 64% which is exceptional for days 11-15. The forecast that lifted natural gas prices at midday was a very cold arctic outbreak into the Central U.S. according to GFS. However, the mega-cluster ensemble indicates that forecast is a distant second choice at a paltry 36% confidence (Fig. 2). Why?
All models, including the GFS, indicate a strong cooling episode across Canada in the stratosphere developing in the 11-15-day period (Fig. 3). Consequently, given the contracting/cooling stratosphere, the weather atmosphere beneath (troposphere) expands and warms. The “most likely” mega-cluster ensemble forecast indicates lack of arctic air generation and increased mild influence from the Pacific which (correctly) defeats the cold.
Fig. 3: The 12Z GFS ENS cooling stratosphere across Canada in 324 hours.
Expect less cold 11-15-day forecasts tomorrow.