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As many know I have been rather negative towards any chance of a cold spell into Xmas and even extending into the New year. However despite the ECM continuing to be poor, im not as confident as I was yesterday. What has raised my interest is the fact that the GFS Op is continually being an outlier and when that happens I take note. However im not confident of the GFS being right either. When you have such a big difference between the models it raises doubt in my mind that any models are correct for the period in question. I do think though that Tamara, GP may think the GFS is a little too early in bringing in the E,ly. So in summary I haven't a clue what is going to happen for Xmas!

thats good news SS. i'm glad you told us that....

Folks, since we've had one instance of it this afternoon, just a warning. One of the biggest bug bears on this forum from moderators and other members alike is those who post off topic posts in here with a disclaimer of "Sorry mods, off topic but...". There are no buts about it, just don't post it.

Thinking aloud somewhat here.. The Alaskan ridge development has sound backing. What looks most likely is that this will shift poleward in the Christmas period. Towards the end of the year, GFS again develops a ridge over Scandinavia (was there on the 00z GEFS). I think fair chance of this occurring although timing is open to question. The two features occurring at the same time - natural evolution would be for some sort of Arctic ridge to develop. That way lies cold Nirvana. Either way, GFS continuing to bang the drum for a colder take on the New Year.

Operation Save Christmas hangs on the GFS trend being correct! The ECM hits the buffers early with a poor upstream pattern. However NOAA have not sided with the ECM and have highlighted huge uncertainty . More about that later after my coffee!

21st to 22nd of December remains an absolute moving feast of anything and everything as far as modelling is concerned. Sorry for plugging in strat charts on NWP thread but entirely relevant and imprints on model volatility imo. Dr Butler showing interest in flux events 'if verified' that's good enough for me given the body of work delivered. In 48 hours things go from one extreme to another.. And a helluva bunched up vortex Neat cold pool building out east... And just for fun the wacky analogs go for a prime year as top analog two days in a row...one for the history lovers / statisticians.. am sure many of the other cited years were horrendous!, nevertheless - adds to the really enjoyable viewing this season..

One thing GEFS and EPS are agreed on: the sub-tropical ridge in the Atlantic is pulled well to the SW over Bermuda during the longer term. That either leaves Europe with a Scandinavian or Euro ridge as a final destination for this phase.

Um, no. Unless you are off on holiday next week? "A tropical climate in the Köppen climate classification is a non-arid climate in which all twelve months have mean temperatures of at least 18 °C (64 °F)." Edit: Ah, unless you mean comparable to half way up Kilimanjaro?

no way the clusters at day 15 would lead you to think that 30 dayer was coming. I have seen this before on the extended and I suspect that either glosea is firming up on a SSW or they are happy to take the MJO into 7 and 8 as being strongly likely. perhaps both !!

Have posted plenty Loch an eilein pics on here before so you'll be sick of that sodding loch ?? but it was just glorious there with the dog today, took him a few miles up the Lairig ghru hill pass looking upon the Cairngorms. Crisp cold, everything frozen solid and some blue skies adding to the scene Drain pipes hanging in there at the house but starting burst off in parts, sign of a potent cold spell Squirrel pondering life (mainly nuts) -1.8c with occasional showers

At T192hrs what we need to see is a shortwave forming at the base of the upstream trough heading se and cutting off the high, this will force the high centre to shift west and bring lower heights to the south. We need a more amplified upstream shortwave circled red to downstream sharpen up the flow, this will also help to pull the PV further to the nw as it phases with that. If that happens we could develop a cut off high to the nw and bingo a cold Christmas!

Dissecting every single frame of every single run... this way madness lies. We went through all this 10-12 days ago. The blowtorch didn't turn up and plenty of places had a snow event. Compare like with like, (ie the JH method) and just let the trend evolve. Honestly you'll lose fingernails otherwise.

Operation Save Christmas moves to 5/10. If we can squeeze more amplitude upstream then we could see some interest develop around that time. Perhaps we might be talking about another slider drama!

Good news NOAA have criticized this mornings ECM op run. GEFS HAS TRENDED TOWARD THE REMAINING CONSENSUS. NOTE THAT 00Z ECMWF SHORTWAVE DETAILS WITHIN AND UPSTREAM FROM THE TROUGH BECOME OUT OF SYNC WITH THE MAJORITY CLUSTER BY DAY 7 THU That's part of the problem in terms of it delivering that crud downstream!

paddy power is already paying out ...........

Just looking at some US state forecasts theres hope that the ECM isn't correct upstream. New York state forecast: Thereafter, the forecast is much more uncertain. Downstream shortwave begins to make eastward progresses as ridge flattens. Weak PVA noted in fast zonal flow approaching area Sunday night, which could trigger some light precip. Then, operational ECMWF remains a fast and stronger outlier as this mid west shortwave moves east. This would result in higher precip chances Monday when compared to GFS and Canadian NH. Maine State forecast: For now, have favored a solution similar to the 13/12Z GEFS with a coastal low on Wednesday bringing potentially significant snow. The 13/12Z operational ECMWF shows a coastal low on Monday night, but this solution involves kicking a Four Corners low out of the SW US too quickly and it is not supported by the majority of ECMWF ensemble members. There is though still the complication regarding whether shortwaves in the mid Atlantic phase with the upstream trough as happened on last nights GFS 18hrs run which stopped better WAA up to Greenland. This mornings GFS run avoided that at the key timeframe so even if its correct versus the ECM there are still hurdles to overcome.

Oh dear whats happened to the ECM and UKMO. Both have performed poorly for several days and are now having to climbdown, very unusual to see this given its normally the GFS which has a flat bias. Looks like NOAA were right to berate recent ECM op runs. The once star of the model stage turning into Norma Desmond!

A re writing of history in favour of gfs ...... if this day 7/8 amplification verifies then it is the first time the ecm has been consistently wrong thus far gfs has been less bad than previous years but to say its wiped the floor with the ecm really isn’t correct Most of the ops post day 7/8 haven’t been good The gefs suite splits the vortex Asia across to Alaska at the end. The height rise to our north/northeast gathering pace for the new year

the 06z is less amplified earlier on, seemingly struggling to get ridging up towards scandi yet we end up with this beauty- this recurring theme can't be ignored now. the GFS seems determined to give us that scandi high by whatever means. as it stands, i think the only uncertainty is the timing. its 'when', not 'if' it happens...

Short one from me - as won't be in the thread again until later Monday - the watch word - amplification, ECM trending towards a more amplified flow as we approach christmas, GFS is holding firm. I expect come 4 days time, both will be resolute with this theme for the last week of the month, azores high forced NW with a trough swinging down NW-SE through UK just 23/24 Dec weekend, possible snow in the north, heights building to the NE, then the azores high sucked back NE elongating and ever stretching towards scandi, setting up a cold frosty high. Could be wrong but that's what I'm expecting to see. So a few mild quite lacklustre days from 18-22 Dec then a change.

Pretty big swing to cold on the 12z GEFS ens...23rd-25th cold members gathering momentum...

GEFS mslp anomalies for days 1-5, 6-10 and 11-15 over Siberia: Add that to already observed: Strong +ve anomaly over Siberia. Comparable with December 2005, but interestingly the Aleutian Low not so classical this time round. January 2006 featured a major mid winter warming.. The Aleutian Low conduit working to effect on wave 1 there. This time round, maybe not so much Wave 1 likely to impact the vortex into January, but perhaps more Wave 2 a possible driver for a strat warming event (QBO was stronger in 2005/6).

I want to believe

Trouble is there are a lot of us thickies watching this thread trying our best to understand the terms used, and what they mean. I know you don't have too but sometimes an explanation for us idiots would really help

A cold xmas gathering pace. A milder blip is well on the cards.. But as thought short/very short lived. Another frame or two on the ec 12z... I would think have some dribbling!!! @xmas-cold

Finally! Barely a wet 1cm but I'm taking it I just walked home through Glenrothes, which was by far the iciest walk I have done in years. More so than in the hills! A & E will be busy today I imagine.

Good to see the ensemble mean pull cold air down across eastern Europe and NW Russia in the medium to extended range, there is a lack of deep cold to the east right now, so to develop a cold pool to our E and NE will set up nicely if an easterly does transpire to end the year or early New Year. In the meantime, we are likely to be stuck with a protracted spell of flow off the Atlantic from the W or SW, perhaps lasting through Xmas, given the colder operationals from GFS (yesterday's 06z & 12z and this morning 00z) were at the cold end or cold outliers of the ensemble spread. But the strong signal for the -EPO ridging to the pole with help of MJO, should in theory, eventually shift the tropospheric PV over Canada and Baffin S and SE, as per extended EPS H500 mean, which may mean a more southerly jet and storm track after Xmas, but perhaps encouraging height rises to the NE which could be aided by cross polar +heights / developing -AO. But a lot of water to flow under the bridge before we may see concrete evidence from the model guidance for a pattern change to bring cold back after it turns milder from the west from Sunday. GFS operationals maybe too eager to change the pattern around Xmas, we could be looking at the period between then and New Year. A fairly reliable indicator of the braodscale 500mb pattern into the extended period is the CPC prognostic H500 charts - which suggest little indication of amplification over the Atlantic:

Great detail from New Hampshire state forecast talking about the overall NH pattern into late December: Overview... Interpreting through late December. Considerable forecast warming in the stratosphere, polar low / night-time jet displaced to the other side of the N hemisphere subsequent of noteworthy anomalous ridging across Northern N America. Beneath which warm air continues to surge into the Arctic from the NW Pacific (with perhaps MJO contributions) and the NW Atlantic displacing colder air S where it becomes bowled up across NE Asia / NE N America. Ensemble means continue to signal an active weather pattern with an amplified H5 ridge-trof pattern over the CONUS, anomalous H85 T warming over the N Pacific with cold anomalies continually reloaded over Central/E N America, however a trend towards higher heights / surface mean sea level pressure with stratospheric cross-polar flow shifting into NW Europe.

Not a huge amount of ENS support but a few with interest and definitely some attempts at Scandy hights and split PVs. A live image of Wanlockhead just to get us in the mood, just to show that there's still plenty of snow still falling out there this week.

just a shame the england cricket team didn't take nick's advice...

Interesting discussions earlier about which model has been performing best at the moment in our neck of the woods. It does seem that GFS has been doing well lately. So while it's quiet, here's some NWP model comparisons. For some reason the European plots wouldn't work, but here's the latest (Aug 2017) RMS error rates (lower is better) for the 500hPa NH forecasts up to 240 hours. ECM clearly performing best throughout; with barely a hair's breadth between the other models at 120 hours; but at 240 hours GFS moving into 2nd place. http://apps.ecmwf.int/wmolcdnv/scores/mean/500_z Next, courtesy of the Canadian Met, the RMS error rates for the 500hPa forecasts at 120 hours each month since Nov 2011 to Oct 2017. I'm assuming this covers forecasts for the USA and Canada. Looking just at 2017, ECM again clearly ahead, although 2nd place switching back and forth between UKMet and GFS. https://weather.gc.ca/verification/monthly_ts_e.html

Just home: All getting a bit wet already but the first lying snow this winter!

don’t think aloud Stewart ........ too many people are listening !! the split vortex and cross polar flow is just waiting to happen but the chances of it actually verifying (and at an axis which hits nw Europe with the cold) remains low. but at least we have a ticket to the January raffle !!

Ecm mean and anomoly finally showing what part of gfs ops has been on the right page and not surprisingly it’s a bit more amplification around day 8 to our west that makes the trough to our east that bit sharper which helps make e Europe colder (spread also has that colder air making a glancing blow to e side uk) Also takes our ridge that bit further north

Snow last night!

If you compare last nights UKMO with todays you can see its starting to resolve shortwaves upstream, note the clean flow today compared to yesterday: So last nights 12hrs to T144hrs: Then compare it to tonights to 120hrs.

The UKMO is out, not as good as the GFS but moving in the right direction. Just need the ECM to drop the misery and remember we're getting close to Christmas!

I like the look of this (aye, it's another Friday!): -8 to -10C uppers right down the east coast...Thundersnow! PS: It's a Saturday!

Happy Christmas from the GFS 12hrs run! Much better than this morning. We do get some phasing with that shortwave but have a better tilt to the upstream troughing.

Just catching up, that is one of the best (for coldies) METO update I've read I think - if it's not an SSW I'm guessing what the GFS is showing in FI has support using their models . I'd sacrifice a cold Xmas for a very cold Jan any day !!

UK Outlook for Friday 29 Dec 2017 to Friday 12 Jan 2018: Through the last days of December it is likely to be unsettled and often windy across much of the UK. Temperatures will be near to or below average and snow is likely, at times, especially across northern parts of the country. Through the first half of January a gradual reduction in the frequency of Atlantic westerlies seems most likely, this will be coupled with an increase in the frequency of colder and drier periods, although confidence is low at this stage. Milder, wetter, and windier spells should become more short-lived during this period with the colder and drier spells of weather bringing an increased likelihood of overnight frost and fog, as well as some snow, wintry showers, and below-average temperatures. https://www.metoffice.gov.uk/public/weather/forecast/gcpvj0v07#?date=2017-11-14

1947 freeze started from a 'displaced Bartlett' whatever the term is supposed to mean???

None at all, MS...That's the point - if a Bartlett is 'displaced' it's not a Bartlett, is it?

High pressure with milder temperatures looks to be the story of next week so there could be some decent spells of weak winter sun around for the run up to Christmas, much better than heavy rain, gales, floods etc anyway IMO

The eps clusters could be very revealing shortly the op not nearly amplified enough at day 9 through the uk and out ne Looking more closely at the spreads there looks to be a cluster which follows the gfs op at day 9 and the eps lose their resolution post day 10 so solutions less reliable after that. Again, expect to see a more amplified cluster percentage than yesterday’s the mean seems keen on a broad Atlantic trough as week two progresses with developing mean sceuro ridge anomoly Putting the two themes together and potentially an extended cluster showing the Atlantic undercutting a developing ridge to our northeast ??? Wonder what percentage that would be ??

well if the update is on the ball then i would expect the 15% cluster discussed with Blue (from ext eps) to start gaining momentum over the next few days. Could be some dreamy synoptics coming into view across the NWP- Yes i know i'm a cold ramper but i genuinely believe things are about to get interesting!!

An Interesting and very marked departure around the Christmas period from the gfs op runs compared to the ens suite A repeating FI pattern from the American model wrt the Azores high building into Scandinavia.So far the majority of both ens suites are having nothing to do with it for now.The one constant though is the Alaskan ridging which shows quite strongly right out to week 2.Just signs that those ht anomalies are building to our east at the end which keeps open the possibility of a cross polar link up of heights splitting the vortex beyond Christmas. Will need to continue to monitor the ens in the coming days to see if this becomes a trend.

I'm starting to worry that we might heading towards a dreaded 'displaced Bartlett'.

Sliding monster.

OK - let's do one of these long posts. Best pacific data very slow to update this week but there is enough out there to put forward a teleconnective update. Not about to contradict anything GP or Tamara have said already today - so forgive a slightly cracked LP feel to things... Much keeps being said about pacific forcing via vertical wave effect of the MJO. With a NH vortex still decidedly unimpressive such forcing perhaps becomes a more significant factor. Current MJO image here as GP already posted: Notice this is a strong signal for significant convective activity. To add to GP's earlier post for those with beginner knowledge the negative blue anomaly just to the NNE of Australia is the specific zone for a 7/8 orbit of energy that pulses north into high latitudes. If anyone wants to see an image of this sort of thing occurring then search for Antony Masiello on Twitter and look at the images he has up on his feed showing wave breaking on the back of the recent Asian MT event and consequent extension of jet energy through the pacific - you see very clearly wave eddies firing north and helping create the Alaskan ridge. Anyway to add a bit more flesh to this... the SOI has flipped negative over the last 3 days following a month of moderate Nina style positive values, indicative of pressure patterns shifting towards a more Nino-esque style, tying into the MJO 7/8 orbit which is also more of a Nino signal. Once again, as Tamara has already described, evidence of the very east based nature of our Nina and how in the western pacific we are actually experiencing higher than expected AAM input than in a "standard" Nina year. This graphic from last week shows the above average surface SSTs in precisely the MJO 7/8 sector with colder water further to the east - and recent running graphics show this colder anomaly perhaps to be fading further to the east Consequent MJO forecast looks like this - and it seems to me that after a long spell of misreading the pacific signal the ECM ensemble has latched onto this 7/8 phase. Note what I said the other day too - latest CPC MJO update is expecting the progression from 7 through 8 to be slow. If you want cold this is good news. The longer it sticks in a 7/8 orbit the better.... All of this would lead to reasonable speculation that reamplification is imminent. I use a fairly blunt JMA tool for MJO composites, but phase 7 broadly speaking pushes high pressure towards our N and NE: and once into phase 8, perhaps around Xmas, the forcing is trying to bend the pattern like this: = a cold signal. Once we transition to January then this lovely forcing appears: What else can we glean? Look upwards we have a vortex profile very much in sync with these tropospheric forcings. Vortex below 50hpa has nothing at all impacting to our west in terms of encouraging a strong westerly pattern: taking the day 5 forecast at the outer edge of reliability the vortex is clearly off centre towards Asia and run forward to the 10d forecast and this is enhanced further: and meanwhile closer to the surface patterns we experience the 10d forecast is demonstrating that the vortex remains a very poor player this year in terms of driving westerlies at us: Notice the ongoing strong signal for wave 1 warming... most certainly going to be reinforced by the alaskan ridge set perhaps to retrogress, allowing opportunities for a bit of aleutian low "kick the vortex where it hurts" action as we approach New Year. I believe the Met have gently indicated their models are seeing some warming impact - it will be this north pacific situation creating it. Is there anything left to throw a spanner in the works? Only really that the best pacific data we have on torques and the angular momentum budget globally has not updated now for 7 days. That is a frustration... but looking at all this other evidence I am not expecting an update suggesting a swift return to anything suggesting a flat response. I sincerely hope I'm not deluding myself... but regardless of flip flopping model runs trying to get a mathematical hold on these signals I am as confident as I can be that amplification impacts are coming, and that climatological and statistical evidence points to blocking to our N and NE with the atlantic cutting in underneath. The vortex profile to my eye makes this even more likely. Timescales still a bit murky... but model divergence in the days before Xmas now suggesting it may appear prior to New Year and then extend through into January. These teleconnective signals can change.... but as far as my amateur eye feels confident to read them I see no return to sustained westerly mildness. Next week is merely a reset - and once we get blocks in place then microscale analysis comes into its own. Happy watching at the moment. Anyone like to guess what might happen were the wave 1 warming over the north pacific to make a significant... and perhaps mortal blow to the vortex? I'm getting ahead of myself here - but factor this in on top of a trop pattern with blocking in place and cold air established over Europe and..... well..... you get it I expect. I'm going to say nothing more. There arent too many analogues for a weak Nina profile working alongside a weak vortex that is hit by a major warming in January on the back of a favourable trop pattern. Go find some... :-)