World Climate Serviceさんのイラストまとめ

Coast-to-coast U.S. cold leading up to Christmas: an extremely impressive ECMWF ensemble-mean signal at day 14. Big shift towards prolonged -AO blocking in the 12Z run today. Wow!

Relief will arrive eventually for N India and Pakistan: the seasonal models point to an unusually cool, wet, and cloudy #monsoon season ahead. (Last year's forecast was similar, but the signals are much stronger this year). Monsoon rains still some weeks off, however.

The latest 35-day GEFS shows a very strong warm signal over N Europe for week 3: 80-90% chance of significantly above-normal temps for most of Scandinavia. It's rare to see such a strong signal in these calibrated (reliable) probabilities at week 3 -> higher confidence than usual

@weather_king Remarkable! Interestingly the temperature forecast was really quite good, but for the wrong reason, as the MSLP pattern was profoundly different near the British Isles

ERA5 reanalysis shows the impressive North Atlantic wind field associated with #StormDennis earlier this month. But despite the stormy pattern, this winter's peak winds in UK & Ireland have generally not reached the highest levels of past decades (per @CopernicusECMWF ERA5 data)

1/2 Looking at ERA5 wind from last weekend's #StormCiara, Sunday saw a swath of 30 m/s gusts (67mph, 108km/h) from Greenland to NW Europe. The area affected by 30 m/s was up to 1.3 million sq-km mid-afternoon on Sunday; the ERA5 North Atlantic record is 2.3 million (Dec 15, 1986)

Let the strongly positive AO phase commence... for context, top historical Jan 1-15 +AO values are +4.3 in 1993 and +4.1 in 1989.

There's a long way to go this winter, but chalk this up as a big win for the seasonal dynamical models, which have been steadfast with +AO/NAO.

NASA's latest seasonal forecast for January-March looks remarkably similar to last February's pattern from the US to Europe - and that was a month to remember (record cold in the western US, 20°C in the UK)

In recent days the CFSv2 bias-corrected 10mb forecast (50-80N westerly wind) for late December has shifted from a weak stratospheric vortex to stronger than normal. Seems to coincide with a potential reversal back to high pressure over NW Eurasia (+SCAND index)

As of yesterday, northeast Pacific area-average SSTs are more than 2°C above normal, according to @NOAANCEIclimate OISSTv2 daily data. This is well above the peak warmth of the "warm blob" years (2013-2016). It's been a remarkable run up since May.