The recent arctic air regime affecting the U.S. and producing, on average, 1-in-50 year extreme cold was initiated by a stratospheric warming event over northern Canada Dec. 21-25. The pattern finally changes and the stratosphere is contributing. In 10 days the operational European model indicates WILDY cold temperature anomalies over eastern North America with even more impressive warming across northern Europe.
Keep in mind, these temperature anomaly forecasts are in the STRATOSPHERE which is the layer of the atmosphere above the troposphere where weather occurs. When the stratosphere cools and contracts the troposphere below expands and warms. When the stratosphere warms and expands, the troposphere below cools and contracts. Classic examples of the two phenomenon are evident in 10 days as indicated by ECMWF (Fig. 1).
The cooling stratosphere over eastern North America causes robust warming at ground level. The ECMWF forecasts temperature anomalies of +20 to +40 across the Northeast U.S. to Quebec in 10 days (Fig. 2). Conversely, the stratospheric warming over northern Europe causes Russia to tumble to 20-40 degrees below normal, an air mass even colder than what the U.S. observed recently.
So…the cause of the U.S. super cold in late December/early January returns after mid-month this time affecting Russia. The new big chill spreads through Siberia which can be a source region for arctic air to the U.S. if cross polar flow develops. We’ll need to watch February closely for the potential return of more arctic air in the U.S.
Fig. 1: The ECMWF (model) day 10 forecast of temperature anomalies in the stratosphere at 10 MB identifies an intense warming event over northern Europe and cold event across the eastern U.S.
Fig. 2: The ECMWF (model) forecasts surface temperature anomalies caused by the stratospheric regime above including 20-40 degrees F above normal in the eastern U.S. to Quebec and 20-40 degrees F below normal across Russia as the next super arctic air mass evolves.
