Winter May Finally Be Ready To Move In

After a seemingly never ending stretch of mild and snowless weather there are signs of a major change to the hemispheric weather pattern by next weekend.

The Arctic Oscillation has been strongly positive with a very powerful polar vortex over the North Pole. This has effectively kept cold weather bottled up in northern Canada. The ice cold stratosphere north of the Arctic Circle is beginning to warm and that warming is going to dislodge the polar vortex from the North Pole and bring winter to the United States by 1/16 or so.

Here’s the 500mb height anomalies on the European computer model for next weekend (day 8-10 ending on 1/16).

This is a total change from the pattern we’ve been dealing with since Thanksgiving. The +EPO Alaskan vortex is gone and replaced by a strong ridge over the Bering Strait which is helping to dislodge the PV over the North Pole. In addition a brief +PNA spike with ridging on the west coast helps send cold south.

Besides changes in the troposphere the changes in the stratosphere are impressive with a notable warming over the North Pole and disruption of the polar vortex. Here is the 10 day 30mb Euro temperature forecast. Between D0 and D10 there is a nearly +25C warming at 30mb at the North Pole. Definitely a change.

Beyond Day 10 the pattern remains chilly for the northeast with the +EPO nowhere to be seen and a -AO. The presence of a -AO has a big impact on temperatures across the U.S.

For people who want snow I don’t think this will be a prolific snow pattern with little upstream blocking (i.e. +NAO) but I do see seasonable to at time below normal temperatures for the second half of January. No question this is a major pattern change across the northern hemisphere. The question I have is how long does this change last – will it stick around through February? I don’t know.

If I had to guess I could see two wintry threats one around 1/16 with a clipper-type system and another around 1/21.

No Festivus Miracle – No Sign of Winter

What a dull stretch it’s been! The weather pattern across the northern Hemisphere has returned to where it was in the beginning of December. Low pressure over Alaska and Greenland means an exceptionally warm +EPO/+NAO signal for the northeast.

December so far has been near 6 degrees above normal in greater Hartford and though we’ll shave a bit off that over the next week there’s no question the month has been an unmitigated torch.

Here’s the GFS ensemble mean anomalies for 1/1/12 (the Euro ensemble means are fairly close).

The substantial negative height anomalies over Alaska and Greenland show this pattern isn’t going to get much better for snow lovers. Transient ridging in the +PNA regions (western NOAM) may deliver brief cold shots and keep New England a bit cooler but nothing too cold. I fully expect the next 15 days to average above normal and likely most of January.

To show you how bad the +EPO/+NAO (negative heights over Alaska and Greenland, respectively) here are the sfc T correlations.

Put them both together and that’s a pretty lethal combination for cold. At the same time there doesn’t appear to be a mechanism to dislodge the current pattern. For example the MJO has entered a dormant phase and does not look like tropical forcing will be able to dislodge the Alaskan death vortex.

Torch on!