Vandaag heeft Stewart een nieuwe update gegeven.
Big, big spike in tendency of relative angular momentum showing up...
http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltend.sig.90day.gif
and there's a big + Asian Mountain Torque in there which will: extend the Asian Jet into the Pacific setting up the conditions for the Aleutian ridge; and, bring about further wave breaking into the polar stratosphere for the next 10-15 days. It was a similar spike in angular momentum which preceded our cold outbreaks of the last two winters.
The ensemble means have, if anything, begun to lock onto a negative Arctic Oscillation with the 'switch over' centred around 11th January. GEFS control going through the floor. Most of the +ve anomalies centred on the Pacific and Siberian sectors.
http://policlimate.com/weather/oscillation.html
Long range tools indicate temperatures for our neck of the woods trending average or slightly below given night time frosts although there is something of a change in the pace of change during mid month as the possible double whammy of tropospheric changes and stratospheric warming (this one a plausible major mid winter warming) coincide around this time.
Northerly attacks along a trough dropping into Europe look the most likely pattern from mid month, potentially going more unsettled as the trough expands into the Atlantic - cold zonality anyone, followed by a genuine cold source Scandinavian ridge ?
Uitleg over Mountain Torque
The MT events deflect the Rossby waves as they pass over the mountain ranges. This can be to latitudes further south and dispersion occurs, or into the stratosphere. If the wave has sufficient amplitude then it can break into the stratosphere rather like a wave over rocks into a settled rock pool. The stratospheric polar vortex, of course, is not a settled rock pool, but a strong circular rotating vortex with a barrier at its edge of higher velocity winds, but this barrier (known as the surf zone) can be broken into, if the wave is strong enough. Hence mountain torques affect the polar vortex by allowing collections of warmer air just outside the surf zone, to be introduced into the vortex, weakening it and displacing it from its central position.
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