Despite taking yesterday off, there’s no change in the medium and long range idea. The Arctic Oscillation is ready to go back negative as heights build north. A ‘bridging ridge’ between Alaska and Greenland towards the end of the month could lead to a major cold outbreak for the Lower 48 and not just a cold blast which hits and leaves but hits and holds given that the NAO is going to get involved, sealing off that eastern exit point for troughs which up till now have escaped from.

Firstly, take a look at the similarity between the 500mb geopotential height anomaly analog over the Northern Hemisphere based on the next 30 day atmospheric ENSO index and the GFS ensemble day 7-14 and 9-16 day.

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GFS 7-day mean 500mb height anomaly

The models have a storm next week which could quickly rebuild the US snow pack which has dropped to low levels for the time of year.

At 27.6%, it’s the lowest coverage in the past decade for the time of year according to Michael Ventrice.

With the pullback of arctic air and the much more dominant zonal-pacific pattern becoming the driver, record warmth has spread west to east.

Before 5am this morning, a tongue of warm, moist air flooding north from Texas to Minnesota ahead of a frontal boundary, boosted the Twin Cities temp to a record 51 degrees this morning.

Yesterday’s highs.

There is colder air pushing in behind the front and sure, the warmth is erased and we’re looking at a potential snow storm this weekend.

Latest ECMWF snow forecast at 168h.

The polar vortex has been strengthening since the start of December hence the pullback of the AO to positive but notice the warming at various levels within the stratosphere over the next 10 days which supports the split and rerelease of reinvigorated Arctic/Siberian air back south into the United States.

30mb

Initial

168h

240h

50mb

Initial

168h

240h

70mb

Initial

168h

240h

The above warming from Asia into North America at 30, 50 and 70mb fits well with the building of heights northward over the continent towards the Christmas-New Year week onward.

See video for more.

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Tags: arctic oscillation, cold blast, north atlantic oscillation, stratospheric warming, US Arctic Outbreak