From October to early December, cold has favoured Eurasia while it left North America out. From particularly November, a steep temperature gradient over Asia led to a stronger than normal Pacific jet and this in turn deepened the Aleutian trough which drove warm oceanic air across North America.
However, a shift in the 50mb stratospheric temperature profile over the last 10 days with warm core centring over the Canadian Archipelago and cold core centred over Scandinavia, this has translated to a cold cross-polar flow pattern and feed of arctic/Siberia air into North America but in turn drives an Icelandic trough.
Current stratospheric temperature profile at 50mb.
The GFS hemispheric 2m temp anomaly snapshots below show the dump of brutally cold air into North America and warm Western Europe in a downstream response.
Credit: Tropical Tidbits
Credit: Tropical Tidbits
Credit: Tropical Tidbits
Credit: Tropical Tidbits
This steeper E NAMER thermal gradient has significantly strengthened the Atlantic jet and thus driving Atlantic air into Europe.
Credit: Tropical Tidbits
Credit: Tropical Tidbits
Credit: Tropical Tidbits
When looking at the above, many will quickly come to the conclusion that winter is already over and we got our limited snow and cold during November and the beginning of December. We’re going back to the same disappointment as recent years. However, I don’t see the weak PV maintaining the current profile that it’s currently in, supplying North America with cold and that’s it. The fluid nature of this years PV I think suggests that it could easily go back to the same setup as before and the GFS is indeed hinting at that.
Note in the below 168 hour 50mb temp chart how the warm core shifts to east Siberia while cold core repositions within the western Arctic north of Alaska and another area of warmth positions over southern Greenland. This to me would correlate to a building of heights stretching from Hudson Bay across Greenland to Scandinavia.
The CFSv2 from days 11-15 begins to reflect the 50mb with 500mb pattern by pulling heights north and the building cold over Eurasia could drift west beneath a Scandinavia blocking high.
Credit: Tropical Tidbits
Credit: Tropical Tidbits
When looking at the GFS 50mb temp profile out to 240 hours, there’s two distinct warm cores on our side of the pole. One over Greenland and the other over Scandinavia which is favourable for cold returning to Europe as indeed the UK with easterly flow.
Keep in mind that the current and projected temp forecast both up at 50mb and down to 500mb supports BUILDING cold over Eurasia and so IF we managed to shut off the Atlantic again and trigger an easterly flow, our source would be nicely charged up with cold. Another thing, it would be late December/early January by the time this would take place. Right in the heart of winter!!!
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