Re : Gavin

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Het is maar een visie. Die van de zonneactiviteit is ook nieuw voor mij, er was meen ik een KNMI-publicatie die de link met het winterweer ontkrachtte. Dat over de hogedruk in oktober is mij ontgaan, de man spreekt inderdaad onduidelijk. Ondanks alles vind ik zijn presentatie wel de moeite waard om te volgen, alleen al de sfeer.

Vorig jaar verwachtte hij een normale winter voor de UK, niet goed, maar zeker niet slechter dan onze vriend Judah Cohen. Van laatste dit bericht vanmorgen, spannende ontwikkelingen voor de komende maand. Stratosfeer doet goed mee.

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 positive towards neutral and then reverse towards negative to possibly strongly negative the first half of November, with uncertainty in the AO becoming large the second week of November.

The current negative AO is reflective of positive pressure/geopotential height anomalies in the Arctic especially on the Eurasian side of the Arctic initially in the Barents-Kara seas and then breaking into two pieces with one piece sliding eastward into the East Siberian Sea. The North Atlantic Oscillation (NAO) is currently positive because of negative height anomalies near Greenland. However the NAO is predicted to trend negative the next two weeks as the second piece of the positive geopotential height anomalies in the Barents-Kara seas retrogrades towards Greenland.

With the AO firmly negative for the next two weeks, this favors below normal temperatures across large portions of northern Eurasia especially Siberia. In contrast, because North America will be dominated by mostly positive pressure/geopotential height anomalies, temperatures will average above normal much of next week in eastern North America. The following week with heights predicted to build once more near Greenland forcing the NAO into negative territory, lower geopotential heights and colder temperatures are predicted first for Europe and then for eastern North America for week two.

Eurasian snow cover is above normal and is continues to advance at a steady pace mostly across eastern Eurasia. However when the NAO flips negative, I expect a more rapid advance of snow cover westward towards Europe. 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 predicted to significantly weaken into early November. All weather models now predict an unprecedented and significant early split of the stratospheric PV. I expect the circulation anomalies associated with the PV split to descend into the mid and lower troposphere later in November. When this occurs expect the cold and snow that has been mostly confined to Siberia so far, to expand into the mid-latitudes resulting in an early start to winter weather for widespread portions of northern Eurasia, including Europe and East Asia, and possibly the eastern United States (US).