https://www.aer.com/science-research/climate-weather/arctic-oscillation
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De summary:
Summary
The Arctic Oscillation (AO) is currently negative and is predicted to remain negative over the next two weeks. The AO is predicted to first trend negative next week towards strongly negative and then reverse towards neutral while remaining negative through mid-November. I expect large model volatility due to challenges predicting downward propagation of circulation anomalies due to ongoing weak polar vortex (PV) event.
The current negative AO is reflective of positive pressure/geopotential height anomalies in the Arctic especially near Greenland and the Laptev Sea. With strong positive heights over Greenland, the North Atlantic Oscillation (NAO) is currently also negative and is predicted o remain negative over the next two weeks.
With the AO firmly negative for the next two weeks, this favors below normal temperatures across large portions of northern Eurasia especially Siberia. With the NAO also negative, this also favors relatively cold for Europe.
In contrast, because North America will be dominated by strong southwesterly flow and mostly positive pressure/geopotential height anomalies, temperatures will average above normal much of next week in eastern North America. However for next week a pattern transition is suggested by the models. Geopotential heights are predicted to build across Western North America that coupled with high heights near Greenland will force lower geopotential heights and colder temperatures for the Eastern United States (US) week two.
Eurasian snow cover was observed to be well above normal across Eurasia for the month of October. Also Arctic sea ice growth has been tepid. High Eurasian snow cover and low Arctic sea ice in the Barents-Kara seas favor first, a strengthening Siberian high and then a weakened polar vortex (PV) in winter.
The stratospheric PV is currently very weak due to an early split of the stratospheric PV with no meaningful recovery predicted. I still expect the circulation anomalies associated with the PV split to descend into the mid and lower troposphere later in November. The PV split is already resulting in the cold that has been mostly confined to Siberia in the month of October to become more expansive. One cold air outbreak is already occurring across East Asia and a second should take place across parts of Europe over the weekend and into next week.
The AER preliminary US winter forecast has been posted to the NSF website: https://www.nsf.gov/news/special_reports/autumnwinter/predicts.jsp. I share my current thinking below.
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