A messege to all you cold weather fans across the US. Do not start crying about the frying that starts December. Yes, it’s going to get mild, how mild? 1, 2 even 3 day departures of 10-20F ABOVE normal, ouch! The good news is however that there is a ton of frigid air over a large chunk of Canada and we have a pattern which favours this coming south eventually. This will not stay there throughout December and in fact the models show this coming south. While mild over the majority of the next 10 days, there is fun and games to be had however along the Northern Tier with a frontal boundary which is kinda stalling out with warm air trying to build north and east from the west, southwest, while the building cold over Canada tries to get south.

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The overall jet flow is zonal through the weekend and into next week but there is of course systems slamming the West Coast and these bare watching as they move inland. The firehose of moisture will bring potentially historic rains to parts of California over the next 5 days but this energy transfers across the country in the form of very mild air. This air should heat considerably as it races over and down the Front Range, so 70s is back on the table for the western High Plains while 60s should dominate the eastern Plains and Ohio Valley, 50s for Minneapolis, maybe another couple of 60s for Chicago?? Certainly mid to upper 50s I think.

Here’s the ECMWF for this weekend.

Saturday.

Note the tightening of the zonal isobars coming into N Calif. Also notice the stronger upper heights to the east of the Rockies, this shows the work of an upper ridge and downslope warming which is heating the air. Also notice it stays cool in the Northeast.

There’s no change except the warming intensifies across the Plains. But below shows Monday and you can see the trough digging some over the PNW, this starts the process of suttle changes for the Northern Tier.

By Tuesday a storm intensifies over the Dakotas and Minnesota, to the south it’s mild, the the east it warms further as mild air gets driven north ahead of the cold front but on the backside, arctic air which is never far away from the barbed wire fence, gets pulled south, so perhaps a snowstorm, even a blizzard over eastern Montana and the Dakotas Tuesday into Wednesday next week?

By Wednesday, ridging advancing north up the spine of the US/Canadian Rockies is helping tip some of this arctic air into the Great Lakes.

The pattern this year is strikingly different to last year where we had a persistently negative PNA and positive NAO/AO.

The growing Canadian snowpack heralds a sign of growing cold which can be seen clearly in the Dec 12 GFS ensemble. Once that PNA flips positive and we get the ridge building north up the west side of North America and that dam will be broken and the motherlode will come south. The later stages of week two may see the process commence piece by piece, before a major cold surge comes down. The thing is, it’s there to be seen, it’s just a question of when.

Below is the 6-10 day off the SPC. Rather warm looking eh?

Now check this GFS ensemble for mid December and pay attention to it. This should excite!

 

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