As we wind down the warmest December on record (by a large and impressive margin) our computer models are now showing an exceptional pattern change that should have cold and snow lovers jumping with joy.
It appears that one of the catalysts for this change is a giant and anomalous block that forms over the Kara Sea. This area north of Siberia in the Arctic Ocean will be ground zero for a pretty big change in the atmospheric circulation.
This super-block effectively disrupts the tropospheric Polar Vortex over the North Pole resulting in a rapid warming and a switch in the all important Arctic oscillation from positive to negative. You can see that dramatic switch in this Arctic Oscillation plot from Ryan Maue at WeatherBell.
This is a very impressive signal on an ensemble mean in the 10-15 day range! The flip in the Arctic Oscillation will allow cold to come south and should really kickstart winter. The 500mb anomalies forecast by the GEFS (the Euro Ensembles agree to a large extent) are very tasty with a classic looking northeast cold/snow pattern developing later in January – especially near or after 1/10.
So how long will the pattern remain “good” for snow? Who knows – but at least there’s a nice looking window for some fun!