Glacier Point

It's all automated stuff I know, but gives an insight into their fine mesh raw model outputs

Hello, Met Office app now showing 80% chance heavy snow 21.00 here. Northward correction there '*if* this is to be believed...

Still look to have potential. I have the SSW maxing in impacts end of month.

What ! Man the barricades. Send scouts to somewhere near Halesowen. Oh, and watch out for these sneaky Wolveramptonites trying to pass themselves as Black Country. 06z runs not great viewing with PPN struggling to get above Bristol. All eyes on the radar for an upset if there is to be one. Key area looks like that push in the band towards Pembrokeshire.

EC 06z rolling out, more elongated with Thursday's low and ppn further south. Midlands on pivot point

EC 06z (yes that’ s not It a typo) taking the low through Brest south-east track). PPN to the north, but not much

Day 9 sees GEFS mean Griceland ridge. We continue like this, and the pressure will be on for the Canadian lobe to de-camp and shift into the Atlantic. That's with a likely well entrenched cold pool across NW Europe. Go figure !

Key thing to watch over the coming days is whether that mean T850 can get to -10 or below around the 27th/28th. Parallel 06z sort of painting a picture of what is the most likely trend towards early Feb.

Actually more like 06z control, and imagine that being undercut. Repeat: Euro trough going nowhere (and I;m taking more February here).

Extended ensemble means starting to reduce the Western US ridge in favour of Alaskan / Arctic ridges. Will be interesting to watch this trend as it opens the door for more westerly flow through the southern arm of the jet and undercutting . The Canadian lobe of the vortex should have no restraint and will bleed eastwards. The high expectation for February is for low pressure in the North Atlantic currently where we have a programmed anomalous ridge. That looks a reasonable bet given the cold air in situ currently Hudson Bay. The blanks to be filled in ... _____ pressure over Greenland .. ______ pressure over Scandinavia. Clue: one will be the inverse of the other.

Once again, Euro trough omnipresent. Once we get cold, the permutations are all loaded towards the cold variants.

Touchdown. GEFS mean AO values for 25th onwards around -2SD. CGEM +1 for the same time scale off 00z. Not sure what's going on there, but fair chance model is not picking up this downwell signal.

Beyond all the model noise right now, one constant. That Euro trough is omnipresent, and an unusual feature in its persistence and depth. Once that becomes cold next week, the permutations become inherently wintry, and to a large degree self perpetuating. Whether that's mid Atlantic ridging pronounced enough to force an early Greenland ridge, jet dropping to our west on a NW-SE axis, cold Scandinavian ridges.

GEFS undergoing major correction towards EPS in the day 8 / 9 range in the NE Atlantic, and that substantively opening the door for Greenland height rises days 12+

Wowsers, GEFS and EPS couldn't be more different in the North Atlantic through day 10. Some crunching of gears coming up for one or both of them soon. Tempting to identify downwelling -U wind anomaly signal as the culprit here.

So here's where it feels like we're playing meteorological Russian roulette, only the bullet is a marked step change in the hemispheric circulation towards a -AO / -NAO regime. Control run 06z GEFS goes from this .. To this ... In the space of 6 days. The Control has the same data as the operational, so it's not a question of data differences, rather resolution although at that range resulting in differences between ops and control. High resolution on a broad scale change isn't necessarily a good thing. GFS Northern Annular Mode projection, in line with AO forecasts, suggesting strat downwelling now coming into view. MJO also arriving in phase 7 at the same time, which would be conducive to blocking formation.

Thing is, they effectively are showing that. We have full house. GEFS, EPS & CGEM means all now showing glowing +ve height anomalies in the day 12-14 zone over Greenland. Notable all three back the Pacific trough west with the EC most aggressive with the consequent pull west of the Pacific ridge. This signal becoming big stronger as runs proceed, against normal climatology drift. This allows for the Canadian lobe to be pulled south and west in the gyre of the North American trough, in turn allowing space for the Greenland ridge. Suspect this is tropical forcing week 2 acting in concert with the signal high aloft

GFS warming a likely reaction to tropical wave / +EAMT in the extended period. Not sure how receptive the stratosphere will be to this given what's happening right now. QBO west unlikely to have much impact I think, particularly as it will be weakening in the next 2-3 weeks as the band of equatorial westerlies is pulled poleward in response to the SSW. I posted similarity with 1986 event to illustrate likely timescales but this one occurring a month earlier, so not a total match up. 1984/5 also running close to a top analogue.. Going to be a long old road to spring proper, and this event, as last year, going to provide a solid basis for sub-seasonal and inter-seasonal forecasting.

Reasonable to conclude two things at the moment: 1: There will be a transition to colder than average conditions day 5/6. 2: The upstream flow across the southern tier of the US prevents any toppling of the ridge to our west and allows a second incursion of Pm air day 10, which entrenches cold into the European trough (more appropriately heads the jet NW-SE into the base of the trough advecting cold westwards). Days 10 - 15 see further loaded potential to what has been advertised by the GFS op.

Putting some index figures to the EC weeklies, AO mean is forecast to tank negative by early Feb late Jan for the week 3 - 4 period (mean -2.5SD) with the NAO also moving to around -1SD. Both remain negative for the entirity of the run. For that week 2 to 3 evolution, which must see a developing Arctic ridge most likely in combination with enhanced sub-tropical flow across North America to displace the lobe of the polar vortex further south and west from its current modelled position. Week 3 could still be a bit wobbly on that, given what we know about the stubbornness of the vortex in this location. On the plus side, good reasoning to think tropical wave development will swing back rapidly to a positive forcing forcing for -NAO during this period. I also think there is a good case for suggesting the downwelling of -U wind signal from the SSW will finally be realised during this period.

New EC weeks 3 and 4 as you were. High pressure in all the right places.

Not sure what all that business days 6-10 was all about on the 12z GFS, but UKM and GEM advertising well the early stage development of the cold pattern. GFS does show loaded potential days 8 onwards with shallow long wave troughs running through the southern tier of the US off the Eastern Pacific. Their interaction with the polar trough once again bringing about significant downstream (cold) ramifications for NW Europe in the extended, as per ensemble broad ensemble guidance. FWIW and purely for fun, days 16-20 on the GFS op would be a redux of 1987.

Hmmm, I remember watching the snow shower at school very well....

Based on where we're at... Impacts look to be sustained and long duration - February into March

Yes, remember this trend in ensembles (all major modelling has this) is against what the models will be inclined to do the further one ventures. FWIW, I'm seeing opportunity for +AAM tendency week 3, which would suggest impending further hemispheric amplification transposed onto a pattern that's already pretty amplified (Wave number 4).