Altostratus

Yes I’m curious as to why strat forecasts at such range would be any more reliable than typical tropospheric forecasts? After all, the cause of the SSW is as a direct result of goings on within the troposphere if my understanding is correct. We all know not to trust the models beyond 120-144hrs so can’t help but be circumspect of these long range stratospheric forecasts. Question for the experts, assuming we get a SSW, what impacts length of time for effects to filter down into the troposphere? Lots of nervous people in the cold hunt thread but surely eye candy charts won’t even be shown yet as they are out of reach. I’ve read various sources that suggest it typically takes a week or two for the effects to filter down into the troposphere. Based on that, and assuming PV split around Boxing Day (as per tweet above), realistically, we should expect to see less Atlantic influence and more HL blocking being picked up by the models from around 7th Jan?

Yup, never a good trend. It looks increasingly likely to me that if we are to get any cold air, it will now be from the east rather than from the north. The current window for GL height increases is diminishing and my fear is that the forecast SSW results in a displacement to N. America.

In Dyce at the moment and some hefty showers have come through. Could be an interesting drive home later if this keeps up.

A dusting of snow at home this morning but as reported by others, nothing in the city. There were a couple of flurries earlier but the sun has now made an appearance.

Just been going through the GEFS and there are some real blinders in there. Out of the entire suite there are maybe only 2-3 runs where the brutal cold in the second wave doesn't hit the UK. It is also clear that there is a growing trend for lows to encroach from the south further enhancing the gradient.

Another excellent GFS run there and very reflective of the ensemble mean earlier. Epic blizzard being shown at the end of the reliable time frame -that would rival the greats of yesteryear.

The fabled polar low

Excellent run from the GFS and shows how important it is for that chunk of deep cold heading under the block to help carve the flow back towards the east. Hopefully this trend will be continued through today's runs.

I did say 'almost' within touching distance. There is only one way that cold pool would head though if it verified like that. Whilst the GFS isn't a bad run you can't help thinking given the synoptic background it would almost be wasteful in not achieving full potential on offer. On reflection, taking a blend of GFS, UKMO, GEM & ICON would probably be ideal for the UK as a whole. Hopefully ECM will align with this blended solution.

That is one crazy ICON run. At 180hr there is pocket of -28C 850hPa air almost within touching distance of the BI!

Yes, the easterly looking less likely this morning but still plenty to be positive about moving forward. The PV remains fragmented, the jet continues to take a southerly track and there are tentative signs the arctic high may exert an influence later down the line.

Looks like a bit of stand-off between the Atlantic and the Scandi block initially. If you look through the archives a similar occurrence occurred prior to the Feb 91 outbreak and it took a couple of attempts before the block could extend westwards. If the evolution is to be similar to Feb 91 (albeit with less cold air in situ), as already mentioned, if would be helpful if that PV chunk in NE Canada shifted N/NW'wards.

I guess it all hinges on whether or not the brief north easterly can deliver a decent layer of snow before the settled clear conditions takeover. Without the expansive snowcover -19C would certainly be off the table.

I haven’t had a chance to check how the ECM Op run fits within its suite but if the Op is well supported, given the timeframe and higher resolution of the ECM model vs the lower resolution of the GFS you’d have to favour the ECM outcome. The GFS is good at identifying major pattern changes but it has always struggled when dealing with the details i.e. small scale features such as shortwaves. Given how sensitive the weather in the UK is to these minor features and the knock-on effect during major changes, you would think the higher resolution models have a better handle on this. Access to the global MORGREPS would help but from memory the ECM is still run at a higher resolution when it comes to the medium range. As others have noted, the UKMO is also in support and historically this model is very conservative. Personally and longer term I’m looking for a ridge to extend into Greenland after the initial easterly - that would be the classical evolution. Anyway eyes down on the 06z...

Nice covering at home and in the city. Hard to tell depths as the wind is blowing it around.

Wind really picked up here in the last 30mins or so. Some impressive gusts starting to filter through.

As reported above, alpine snow, even in Town.

A dusting of snow at home but doesn't appear to be anything in town

Disappointing isn't it! We need a clean northerly flow as this slack flow is doing us no good whatsoever. I went home for lunch and one of the heavier bursts gave a dusting of snow, but nothing but rain/sleet in the city, as expected.

Yup temperatures aren't great (haven't checked dew points but presume they are sub zero) but with light winds and heavy bursts, hopefully some evaporative cooling can swing the balance in our favour.

Radar shows a large shower heading in this direction...hopefully it maintains current trajectory and doesn't fizzle out too much.

Another good run from UKMO and given the position of that low, I don't think it would topple either. I wouldn't be surprised if we are witnessing the classic GFS over-progressive bias here. A high just to the north of the UK looks likely, with hints of drawing in colder air from the East.

Similar story here. I was expecting to get some sleet but was surprised to see everything turn white so quickly, particularly given all the rain.

Heavy snow and gusty winds here. Nice covering already.

I'm not far from the city centre and it's very close to snow as I look out the window at the moment. I suspect it will be all snow further in land.