The image below is from the latest Global Ensemble Forecast System (GEFS) model showing a major upper-level pattern change developing across the northern hemisphere. You’ve heard me refer to the “North Atlantic Oscillation” (NAO), and the “Arctic Oscillation” (AO), both of which dictate the behavior of the upper level westerlies (the jet stream) across the middle and northern latitudes.
In the image above, note the upper-level ridging (bright red shades) fade across the northeastern United States before building in across the North Atlantic (Greenland and northeastern Canada). This pattern shift is indicative of the “North Atlantic Oscillation” shifting from its positive to negative phase. When the NAO tanks (drops rapidly), look out on the east coast for Nor’easters! When the AO dips, arctic air will likely be making its way southward out of Canada into the United States.