IDO

The 12z ECM is more closely matched to GEM/ECM/GEFS means, so is not a wild card. If the 0z was a hero, the 12z is a zero, so something in between. But the bigger picture the means that have been pushing for days, is a ridge, and slow-sinking high towards the UK, then drifting south. This is how the ECM played out but a bit progressive IMHO, so maybe at the milder end of the ens. As for the 12z 10-day ECM -v- GFS, the GFS is preferred with a colder short spell: ECM> GFS>

GFS consistent with its previous runs and the means, in the toppling ridge and the high sinking over the UK. The difference was that on this run, the pattern shifted west so the UK was under the trough and the colder uppers whilst this was happening. So, a few days of cold and snow potential was better than previous runs that were cool/drier. But let's be honest there is no confidence still post D7-8; none of the models may have a fix ATM. The ECM 0z was an unusual chart that we see a few times every winter in the models but rarely they will countdown from D8. So, I envisage no omega block on the 12z, but a shift towards GFS as they meet somewhere on the middle ground. A cold few days look the call, with post D11 still deep in FI. Hopefully we have seen the back of the Atlantic onslaught and things will be more interesting from mid-Jan... London short ens show the slow fall in temps later mid-week:

If we look at the GEM mean post-D8, it is a replica of the GFS op 0z/06z with the Atlantic ridge unable to sustain and the high sinking across the UK: Without the rare omega block of the ECM, there is nothing to sustain high, even mid-lat heights. GEFS 0z also concur: The ECM mean is the same. So looking at the means for higher verification then we are hoping the ECM wonderkid 0z omega block comes off.

The GFS 06z is very similar to the 0Z so we shall see how post D8 goes compared to the poor FI on the 0z: 06z: 0z:

Looking at the GEM, GFS and ECM at D8, the differences are stark, so a lot of uncertainty: ECM gets two lows to undercut the wedge/heights Greenland/Atlantic. It gives a slower sinking high around Iceland creating an omega block with continued undercutting and cold air in situ and with a cold flow. The perfect setup for a mid-lat high, with the lack of forcing for a sustained HLB. ECM 850s:

Bearing in mind the propensity of ECM to overhype heights at D10, I am not sure I would put much weight in that D10 chart. Anyway it is not a cold run; though that is expected. Anomalous 850s: What follows has always been the "potential" and ECM coming into that period over the weekend, so we should see if it can bring in snow and cold rather than a cool high/ridge?

Assuming the mid-lat high is the outcome, and indications are strong, we just need the pattern to shift west. The 06z has mainland Europe getting most of the snow: On this run, cold and mainly dry IMBY. Not really my thing, but better than the current wind and rain.

The GFS is a variation on the mid-lat-UK HP but this time, like ECM and GEM, gets some cold air in as it moves west to east: Ties in with the means.

We can see the standard deviation from D8-D10 on the ECM ens, highlighting the lack of confidence post-D7-8, which was also apparent on the GEFS. Z500 on ECM ens 0z D8-10: Looking at the individual members, quite a few with very cold uppers seem to skew the mean 850s, so I would be wary of taking the mean 850s as a metric of note. From D10-D15, the ECM mean is UK-HP-centric, much like GEM and GFS. e.g. GEM: So, is it looking fine for a drying-out period from D10-15 as all the models' means are concurring ATM?

The ECM mean looks very similar to the GFS op and GEFS mean, also hinting at a variation on the theme of mid-lat heights near the UK: 1. 2. 3. 1. GFS op at D10. 2. GEFS at D10 3. ECM mean at D10 Also, as usual, the D10 chart is an outlier on pressure & Z500:

There are no apparent changes from yesterday from a mean POV, with the GEFS showing no forcing in the whole NH, meaning the slowdown in the westerly flow cannot be aided by a wave attack (showing currently), so we rely on wedges of temporary heights meandering in the flow: D8-16 mean: Again, the Arctic high is prominent until the end of the run but of nominal value for the moment. After D8, when the westerly trains slow, it looks like the UK high (or close by) is still the fav; but the nature of wedges is that if you get lucky we could get a cold snap/spell. The GEFS still suggest variance after D7-8: 850/2m temps: So, no confidence in surface conditions, cold from a high, a brief northerly, or a slower zonal pattern? The GEM and ECM are looking better at D10, but I would not trust these two at that range for all the money in the world. Though undoubtedly possible scenarios. But we want a blocked cold and snowy outlook that is at least 16+ days away based on the GFS 0z mean/op (usual caveats). Though a cool down from above average currently to closer to Jan averages.

As expected, the ECM op at D10 is moot as the op run is an outlier early on in the run via at least two metrics: One for the bin highlighting the uncertainty with taking op runs seriously beyond D7-8. The De Bilt shows that the mini-wave in the Atlantic on the D10 mean will have more significant colder benefits to the east of the UK: Let us see where the 12z takes us. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4985714

Looking at the GEM mean, which moves on from one D10 frame that can be taken out of context, we see a UK high as a distinct possibility: D8-16 GEM mean: The temporary shift away from UK zonal is because the flow is to our north. A variation on that theme would be the call, as there is no upstream amplification, and the Arctic high is not receptive to a link-up with wedges around Greenland due to its polarity.

As expected, the ECM op at D10 is moot as the op run is an outlier early on in the run via at least two metrics: One for the bin highlighting the uncertainty with taking op runs seriously beyond D7-8. The De Bilt shows that the mini-wave in the Atlantic on the D10 mean will have more significant colder benefits to the east of the UK: Let us see where the 12z takes us.

There is no confidence in the tPV shenanigans past D8, so my thoughts are JFF viz details, but I see little sign of any convincing northern blocking right up to D16 on the GEFS—no signs of wave amplification. Relying on wedges and an Arctic high invariably is less helpful than it is. So cold zonal relaxing to a slower zonal sine wave regime as we pass the next two weeks. The GEFS mean is moot for details but can give us some clues as to NH patterns (D8-16): The Arctic High looks like a nuisance by boxing in a pattern unhelpful for sustained high-lat heights, wedgy at best. We are on the colder side, so average temperatures to cooler. Later in the run, the possibility of N/S split as around D10, we see the westerly flow lighten up. The real story of the last month and into the New Year is rain and storms, likely signs of the times. This winter looks to be suffering an extended version of that. As ever, I feel an impactful strat warming is the best shot of a period of cold and snow. As for the MJO signal, that hasn't impressed me in the last two years, dampened by other background signals. I have been burnt 99% of the time with GFS over-amplification of heights in FI, so its recent output is strictly for fun. And D10 ECM, do not get me started! Fingers-crossed those with expert knowledge of an impeding amplified pattern are correct as the models are now close to mid-Jan, the mid-term.

Looking at the ensembles, the scatter is as early as D5-6, highlighting the uncertainty for the next ten days. We will see greater model volatility because there is no forcing, just wedges, their strength, polarity and positions. Look at the wedges 0z v 06z v ECM v UKMO (D6): Subtle differences have a more significant knock-on effect

A few days ago, the FI mean was picking up the Canadian high/ridge and the return of the Arctic high, and now this is showing a good level of confidence: 1. 1.D8-16 GEFS mean 0z I commented then that I was unsure what this meant for the UK other than a pattern change. But this was the pre-cursor of our previous cold spell, so maybe height will rise in the Atlantic sector from week 3. Sadly, that does mean more winter is eaten up with the expected zonal flow in the meantime. Very average, even if the jet does slide further south, as per the GEFS: 2. 3. 2. GEFS mean for London 850s on 0z run. 3. EC mean for London 850s on 0z run. Both show classic zonal, with the GEFS slightly colder, and there is a lot of scatter in FI. However, that is likely the timing of the zonal sine waves. Wet after this remaining dry spell is brushed aside. 4. 4. GEFS 0z 10-day accumulated rainfall shows the west suffering as expected in this zonal onslaught after D3. Other factors will hopefully enter the play as we move through January...

Looking at the GEFS and a strong signal for the Canadian heights and Arctic high to re-establish, putting a hold on the customary westerly flow (jet): D8-16: It looks like a split tPV, but I'm unsure what that means for the UK. Unfortunately, we cannot trust the models in FI about height rises as the last two efforts by the ops have failed as they have entered the reliable. So, a watching brief for early January. As for the short-medium term, the GEFS spread increases around D5-6 (London): 1. 2. 3. 1. Short ENS 2m temps GFS London, spread D5-6 // 2. 16-day GEFS London 850s // 3. ECM 10-day ens London pressure; spread increasing; op outlier territory. Some cold zonality remains the likely outcome for the rest of December, but the timing and the pace of the sine wave zonal pattern are causing the spread.

After all, the models made a meal out of it; the initial thoughts that the end of December would move to a cold zonal pattern seem to be where the models now indicate. Looking at the London pressure mean (red line), that is classic zonality: 1. 2. 3. 1. GEFS mean pressure - 2. GEM mean for comparison 3. Temp-wise, average fare. GEFS London Looking at the D8-16 mean NH, nothing is showing for any amplification apart from the Canadian high. The above-average Euro heights dissipate after D12, which may help for a better UK trough into Jan (e.g. the OP retrogresses to the Azores).

Looking at the D5-D6 differences between how GFS and ECM handle the Azores high, we see the knock-on effect for the difference past that point: The GFS has a cut-off low splitting the Azores High, and that causes a larger block against the Scandi trough, pushing it west to east rather than the ECM, pushing SE. Neither is helpful, though the GFS may fetch some colder uppers around Christmas as the colder air flirts with the UK. That is assuming both are correct regards the modelling of that ESB LP cell. For example, the GEM keeps it in the west Atlantic longer and enables the secondary higher-lat Canadian ridge to sustain longer: Looks like model chaos from D4-5, so until that period is clarified, we are looking at various possibilities.

Nascent heights developing in the Arctic regions from D10 that arrive at this by D16: Another Arctic high. That could explain the slowdown in the Atlantic push and could help with wedges of heights going to higher lat. This Arctic high was not apparent on the 06z run, so it is something worth monitoring.

Much better GFS, slowing down the Atlantic sector. Problem is it is post-D8 again and GFS has had no consistency of late. But here is hoping...

Another variation on a theme from the GFS 12z, with a similar outcome for around Christmas of a bride spell of colder uppers. 06z and 12z: Christmas eve on the 12z:

The GFS 06z returns to the Azores cut-off low again, which props up the HP cell for a more angular ridge and a bit colder run, though likely to be just the ebb and flow of a zonal pattern: But we take what we can get so that the 06z may be the best case and 0z the worst.

There is no way to spin it; the direction of travel is away from anything other than a passing ridge/trough dropping some cold air, for barely 24 hours in the south (850s/2m London 0z): There is lots of scatter afterwards, so it looks zonal with the position of the jet to be determined. The GEFS mean at D16 offers little right through to year's end: No sign of forcing from MJO waves. Just the tPV smooching about freely above the mid-latitude HP systems. From my reading, this is much like how December would play out, and we can only hope the rest of the winter offers something more promising.