Thursday, 3 January 2013

Major Stratospheric Warming Event

MJO in phases 4,5 and 6 will cause a very warm pattern until the 15th of january with a ridge in the eastern part of north america and a +NAO/AO combination. The wave will be fairly strong but will propagate eastward quickly, limiting the warm pattern to a fairly short period of time.
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After the 15th the wave will weaken and move towards the COD and could move into phases 7 and 8 later in late january or february but that is still uncertain right now. Phase 7 looks like this in january, notice the east based -nao, +PNA and -EPO pattern with a trough in the bering sea.
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A less amplified MJO wave means after the 15th we need to look for other factors that will influence our weather pattern across north america. An active pattern will likely return mid and late month as an active SE ridge is present with a trough digging into the west/eastern rockies. A large thermal gradient will set up a BZ across the eastern GL, ohio valley and interior northeast. Look for several snowfall opportunities past the 15th as more cold air gets established into the pattern with pieces of arctic air moving down from western canada. Also a very active west pacific LP wave train has set up with poleward movement of frictional torque. This lines up with a weak phase two of the GWO(more of a la nina pattern) and means that we can expect a stormier pattern mid to late month.

Further down the road the effects of the current SSW will take hold on the east as the trough in the west eventually progresses eastwards. An initial warming has already weakened the vortex with warming near the pole but another warming event will take hold across northern canada with rossby waves and a +EAMT reinforcing the warming. This should be enough to cause a complete collapse of the PV. A wave 2 pattern will set up, splitting the vortex with one piece moving onto our side of the globe and another towards eurasia. With a two week lag, expect very cold temperatures to move into the east past the 20th of january. With a strong trough in the west large pressure rises should occur across NW canada which will press against the ridge before the cold wins out by the 20-25th. The GFS is probably too fast with bringing the cold air eastwards which is in line with its MJO forecasts. The ECMENS and euro weeklies are beginning to catch on to the colder pattern and a -NAO/AO pattern caused by the SSW event.
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