Highlight: Stratospheric warming appears in 15 days.
Fig. 1-2: ECM ENS and GFS 10 MB temperature anomaly forecasts in 15 days indicate stratospheric warming.
Discussion: At the surface, forecast models are very warm across the U.S. HOWEVER, trouble may be brewing in the upper atmosphere. The ECM ENS indicates a stratospheric warming event taking place over northwestern North America (Fig. 1) while GFS has this event with higher amplitude centered over Canada (Fig. 2). The GFS forecast is most concerning. If the stratospheric warming is consistent and lasts a sufficient amount of time, northern latitude arctic air may generate. The U.S. gas population weight HDD forecast indicates a warmer trend for Dec. 1-7 as U.S. HDD dips below normal (Fig. 3). A careful eye for possible colder changes in early December if the stratospheric warming becomes established.
Fig. 3: U.S. gas population weight HDD forecast by all models, their consensus, and compared with 24 hours ago and the 10-year/30-year normal.