Kasim Awan

Now all we need is a 350 mile southward adjustment and we're on the money.. The 12z suite so far has shown a good improvement on the initial tilting around Greenland at 120-144h for a clean south easterly low progression & more effective later amplification. See if the ecm/ukmo continues the trend.

I think a good part of the east could would up to a crunchy floor on Xmas morning, and not of the frost variety..

North is the only way.. ❄ #keepthehope..

The icon/gfs has slightly lower heights over the North Sea during Xmas eve. Soundings are conducive for a wintry mix, with snow the main ppn type above 100m inland & in heavier bursts. The UKMO is quite different. This macrodetail will not be fully resolved until T72.

Icon has finally dropped it's unsupported Xmas evolution.

Now we have a trend of good Day 10 charts, rather than just the isolated one, which is what we have been dealing with all winter. Plus, the current northerly (23rd) albeit weak has been modelled well out and verified rather well. No reason why a secondary emerging trend can't either.

In the possible event that low pressure parks up across the UK w/o a surface easterly flow, large snow totals could still develop. Heights here are extremely low, winds light, perfect recipie for prolonged shortwave snow. Take for example March 2016 which saw 12" here at 300m and 4" at 100m. Uppers of -4 (first two images) Compare this to the potential scenario ahead, which in dynamics is almost a carbon copy, uppers a bit cooler and nights longer, great recipie going on here. It's worth noting that the gfs / ecm ens have a mean pressure over the UK of ~ 1015mb at 216h, so this solution is becoming marginalized. EC op is the most realistic solution so far, imho, and seems to fairly reflect all factors at the synoptic level.

P.S. the ECM set an easterly trend following the initial northerly, GFS is now opening up the door to the beast zone... could be onto something.

The "problem" here is a slight build in heights north of Scandinavia which prevents coupling of the main low with the Arctic low, preventing movement of more serious cold. Nontheless, I'd be fine in Buxton.

The 18z gfs has come into line with the ecm quite a bit.

I'm not doubting that the outlook is interesting & potentially cold. I'm just illustrating the potential evolution options around the D6-8 range, for which the ECM progression seems a strong candidate. The expansion of the low is currently a more *favoured* outcome at this range, i.e. a wintry vs brutal northerly at D8-9. Beyond this, one would only speculate what could happen given the likely initial, extremely amplified pattern... ❄

You're missing the point. The ECM 12Z was due to fail the northerly from 144h Low is too big > longer atlantic sea run > uppers get moderated. This is why I remain on the fence regarding the gfs doomsday output

I'm not saying it's terrible; just saying it isn't as fugitive as the gfs for intense cold. As it happens the less amplified solution the ecm is showing us now is slightly more strongly supported in the ens.

ECM again making too much of the low south Greenland / Iceland area. Result is a milder northerly.

ECM looks to be in a good position to make a bit more of the Xmas eve northerly than the gfs.

ECM holding strong out to 48 hours. Some relief...

In theory the ECM should get a better grip on the flow dynamics between Iceland and Svalbard D6-8, icon, gfs and gem all favour dynamics here more conducive of slower development than the local cyclogenesis shown on the ECM 00z. This (should) give us a fantastic ecm run. I'm betting on it anyway.

There may be some sleet mixing on the coast / low levels in the centre of any shortwaves where uppers moderate, apart from this all snow / hail ~95% of all ppn for the 28th there. 525 at 500/1000z, etc etc edit, don't forget the heavy showers would drag down the polar air above. so soundings would change

The GEM is drastically better in it's southwards progression of the low falling a close match to the gfs12z op.. Helped by WAA out of Newfounfland which is key here. However, the speed I feel is another vital factor ECM needs to play ball and decrease the cyclogenesis rates of the low associated with northerly #2. A strong cyclogenesis would whip the low through w/o producing a healthier development of the northern low flank & cold air injection as per gfs & gem (somewhat). All to play for re ecm giving us a SLOWER low attack..

Have you had some of what the gfs is on

12z would likely yield a satellite image like this..

This study analyses performance to 72h and not 96-180h which is the time period I am discussing *potential* weaknesses in the icon.

I never said I was ignoring the icon output. As Mucka said, we are dealing with probabilities here, which are swayed away from the icon solution for reasons discussed .

Seems to always be somewhat isolated in it's output. That's why a gfs/ecm type evolution is somewhat favoured in here etc.

Yes, amplify the high like icon and loose the space for the low waving and secondary northerly. It would be possible to get both the initial amplification / northerly and the secondary hit under a moderately amplified ridge, and I feel the UKMO is a good example of this..