Wednesday, 20 November 2013

December Update

Contrary to any previous ramblings, I am all in for a below normal december based on the current look to the pattern. The NE pacific warm pool will help encourage strong ridging over the aleutians(we are seeing hints of this already with Ca air masses packing a punch from the prairies on east). We are already seeing record cold showing up across the NWT, AB and BC. The bering sea ridge will shift at times into the GOA(when tropical forcing is favourable) creating more of an el nino/la nina hybrid sometimes. Biggest risk right now is if the GOA warm pool backs further west which would have a tendency to shift the coldest anoms into the W and SW part of the continent(unlikely scenario at this point). 
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Indications are pointing towards a favourable GWO in Dec with +AAM dominating the 35-55N belt and easterly momentum dominating the subtropics. This will help encourage the MJO to move into more favourable phases. Roundy plots show this evolution just before christmas with a wave moving across the pacific in tandem with the active KW phase plot.
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In terms of the AO, it should stay predominantly on the positive side this winter with little in the way of any major SSW's unless we see a late winter final warming which could have implications on spring. An overall +NAO and +AO means that we can see some larger temp swings with more of a progressive pattern setting up on average. In terms of the +QBO, Neutral ONI and Smin induced -NAO pattern, we will need to see where the PV sets up in december to see if that theory can prove itself valid. Early indications have the upper vortex over the greenland/siberia area with most of the blocking confined to the bering sea. 

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