The strongest late-spring stratospheric warming of the polar vortex on record really made a mess of signal-based long-range estimations this month. Only as we head into June does the resulting high-latitude blocking pattern look to relax sufficiently for the UK to start seeing some appreciably warm temps. Though mainly the blocking just focuses on the Pacific side and so 'leaves room' for ridges across the UK with LP systems moving slowly by to the north.
The patterns therefore look to remain very stagnant, with little sign of the typical resurgence of westerlies in response to the rapidly increasing thermal gradient between the low-mid latitudes and the high latitudes.
This raises some very interesting possibilities for June.
For example, the stagnated plume of the GFS 00z is not at all unrealistic, and gives me a rough CET estimate for the opening 9 days of June that's in the low 17s. As far as I'm aware, while that would not be exceptional for July or August, it's near record territory for June - which really shows how much the 'thermal lag' plus typical return of westerlies tends to peg back the temps in the UK.
As the Arctic latitudes warm faster than the lower latitudes, with increasingly early onset of spring heating via snow cover loss, I can see this thermal lag becoming increasingly weak in the decades to come, and as such June could be the summer month that sees the greatest warming trend in the UK and N. Europe generally.
Given that the days are at their longest, the potential is there for June to become seriously toasty. I'd not be surprised to see (at least) one June CET in the 18s within the next two decades.
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