Model output discussion - heading into 2018

[MP-R]

Can't post charts easily as on phone but nothing screams organised Atlantic after next week. The GFS 18Z for example shows another low crossing the country next Saturday with cold quickly following. Not your straightforward zonal spell coming up.

In the short term, however, I think flooding may become an issue in some places, the saving grace being quickly passing weather systems.

[Man With Beard]

Gone under the radar that the first two weeks of the EC46 are comfortably below average for upper air temperature! (as weekly means) Quite contrary to expectations of many not a week or two back.

[Allseasons-Si]

On 27/12/2017 at 23:11, bluearmy said:

The only concern on the cold snap end next week being that the op was the warmest run at day 10. Want to see that change on the 00z run.

The ec is in line now BA and ens are still showing a marked drop in temps from the 5th/6th

Edited December 29, 2017 by Allseasons-si

[comet]

Would not want to put any confidence into any forecast 3 weeks out whether it is showing deepfreeze or torch no matter  where its source came from.  The downwelling and warming I spoke of in a earlier post today is again probably the reason for seeing the synoptics  that are showing in the 18z run but being the 18z run without good support from the ECM tomorrow and consistency from further gfs runs then will consign to the bin. We shall see.

[Allseasons-Si]

whats' not to like on the 18z as was with the 12z control with the sliders and runners from early FL,the 18z gfs shows a similar evolution with a runner(low pressure) heading east into the southern BI from 186 then a poss slider from  240 with heights building to our NE forcing the jet SE

2017/2018 winter season hasn't been bad so far with two snow events this Dec and another one tomorrow,and i feel that we may see more of this continued nw-se track of systems going into 2018.

 

Edited December 29, 2017 by Allseasons-si

[joggs]

1 hour ago, Snowy Hibbo said:

EC46 500mb

Week 1 (2-8 Jan)

Week 2 (9-15 Jan)

Week 3 (16-22 Jan)

Week 4 (23-29 Jan)

If you like a mostly neutral AO profile, and a positive NAO profile from Week 2-4... then you are all set.

Absolutely awful for coldie.

[OfficialKevWX]

My thoughts -> Into New Years: After a milder interlude this weekend a continuation of cold zonality is expected, with potential sliders giving snowfall like earlier this month. Not the best way to get snow as it’s marginal but any sustained cold looks to be wk2 jan onwards

[Matthew Gill]

Sorry for my ignorance but I'm only just learning to read the models. On this image does it show high pressure building over to our NE. At the same time frame we have uppers of -4 over most of us. If the low coming across the Atlantic from the USA was to track to our south would this allow a cold shot from the north west?

[Guest]

TRYING TO COME TO TERMS WITH THE MANY CURRENT UNCERTAINTIES

Firstly, I hope that you all had a really enjoyable Christmas in whichever way you chose to celebrate it.

In this post, I want to take a broad look at some of the conflicting background signals, what “appears” to be some pretty inconsistent input data, various other issues and to what extent are the models coping with all this. I will raise more questions than answers and I hope that this will provoke further discussion. Then I will take a closer look at the outlook with one of my cross-model analyses.

The many excellent contributions to this model discussion thread cover such a wide spectrum of material. As each model run is churned out there are those that choose to provide a short running commentary on what they see and often make comparisons to other models and/or recent runs as well as drawing attention to any changes that they detect. There are those that focus on what seems to be driving this output and what might be causing any changes and what we might expect down the line. We see quite a few posters dissecting the model output and assessing the likely impacts both on a micro and a macro level. Then we have those who react to all the opinion. This is normally done in a respectful and constructive way and this becomes one of the great strengths of this thread and what it’s really all about – the “discussion” element. Sometimes emotions run far too high and the moderators might need to step in.

I often like to take a step back and provide a longer report either looking at the overall broader patterns or focus on specific matters coming from a slightly different angle. As I always say, I am definitely not an expert and I have a few weaknesses in some of the more complex parts of the subject (which I do try to point out as I cover any of these aspects). I am a “coldie” often looking for changes to colder patterns but I do try to inject a reasonable degree of balance in what I have to say.

SOME CONFLICTING SIGNALS:

1. The El Nino Southern Oscillation (ENSO)

During the run up to this winter we were told by a good number of the more experienced analysists and/or forecasters that we might expect a “winter on a knife-edge”. In the simplest terms (for my sake as much as anyone else’s!) it looked like we would have a weak to moderate La Nina winter. Together with an east-based QBO this would be likely to favour a front-loaded winter with a colder and drier first third, a milder and wetter middle part and (perhaps) a colder end. As we moved into late November/early December, there were signs that the La Nina was somewhat weaker with the colder currents in the east Pacific and not in the usual more central position. There were some “suggestions” that this might extend the early period of colder conditions, perhaps through December and into January. To counter this, almost all these (let’s say) “well informed” posters mentioned that there were considerable downside risks to the colder evolution. Not least due to the strong seasonal tendency for the PV to be close to its strongest and most well organised from around the December solstice through to early/mid-January, with the jet stream usually around its strongest and most direct too.

Just before Christmas, further changes were indicated in the ENSO state. Firstly, there were indications that the La Nina was starting to strengthen and take up its more central Pacific position and this would once again favour the milder mid-winter scenario. Then there have been even more recent posts from several of our highly respected regular posters, that rather than strengthening, that the La Nina ENSO state was not only weakening  but it was actually exhibiting some rather more El Nino characteristics, albeit very weak (this seems to be in relation to conditions nearer to Australia and may only prove to be a more local and perhaps a temporary conflicting signal).

I believe that these two conflicting prediction signals have come from two different data sources. If so, how long can this apparent disagreement continue? Is it possible that both predictions are partly right? Perhaps with a stronger Nina signal from the central Pacific and a more neutral one from the east? Is it even “possible” for the upwelling and downwelling colder/warmer currents to produce a mixed state in closely adjacent parts of the ocean surface layers? Can some of the measurements be subject to correction? If there is a change in the ENSO state, I imagine that there is quite a time lag for any impacts to be felt and a question over how this interplays with other teleconnections and background signals and which one is the more dominant, both in the shorter and medium term (say one to six weeks).

Given that the ENSO state is often one of the key influences on Northern Hemisphere winter patterns and rarely subject to rapid and unexpected swings, I can understand the current dilemma this presents and I strongly sympathise with all those experts (as a well as experienced amateurs with a good grasp of this part of the subject) who rely on this data.  

Please note that I realise that key predictions in angular momentum (AAM and GLAM) are done in harness with other signals (like the GWO) but I do not have anywhere near a sufficient understanding of these processes (that is interpreting the AAM charts, assessing the impacts and enabling some very useful predictions to be made) to make any meaningful comments here.

2. The Tropospheric Polar Vortex

The tropospheric PV has been weak in the run up to winter. As I said above, it normally starts strengthening (sometimes very rapidly) throughout December, typically reaching around its seasonal strongest at this time of the year. There can be occasional big exceptions. We have seen the PV come under attack from WAA into the Arctic, mostly but not entirely from the Pacific/Alaskan/northern Canadian side. The models produced a whole variety of pretty unusual Arctic profiles during the last few weeks. Most of these initially appeared in distant FI but then came into the more reliable period and are present right now (I focus on this again in my cross-model analysis towards the end of this post). Some charts showed completely split PVs from various alignments (so far, these never verified). Other models/runs showed major disruption to the PV, many with substantially displaced PVs and most (at times) with very weak PVs. A few models showed the PV coming under successive attacks at intervals during the course of a particular run. The WAA attacks usually lead to HP building into and across the Arctic. Many charts actually showed a cut-off Arctic HP close to or over the North Pole and a few charts got very close to a cut-off Greenland HP (the latter charts have, so far, not verified).

When the tropospheric PV remains relatively weak this has (with examples from quite a few past winters) had substantial impacts up to several weeks later on. The cold is released from the Arctic towards the middle latitudes in much the same way as it can be from a Sudden Stratospheric Warming (SSW) event. Typically, as in several recent winters, North America is favoured but sometimes Eurasia is (instead of or as well as) and this can include Western Europe and the UK.

If only it was as simple as that! Unfortunately (for coldies), there are many factors and forces which can change the state of the tropospheric PV. 

3. Impacts from the Stratosphere

Other than the strong seasonal tendency for the tropospheric PV to strengthen, there is very often a strong link with the stratospheric PV. My understanding of the profile of the stratospheric layers and interpreting the various charts is rather more limited. So, in simple terms, from what I’ve seen reported, I believe that there has been uncertainty in respect of the quite near term (1 to 3 weeks or so) temperature forecasts for the stratosphere with some layers warming and others cooling, some recent upticks and even more recent reversals. In particular there was a stratosphere/troposphere disconnect. In a typical winter there is usually (but not always) a strong link between the two. The stratospheric PV can imprint onto the tropospheric PV and this is what I think was forecast. A strengthening stratospheric PV taking up a position close to over the Pole. Then the signal descending through the lower layers towards the surface and aligning with the tropospeheric PV (or rather encouraging the tropospheric PV to both strengthen and move into a closer alignment).

If what I say in this part is “broadly” correct, then I have some questions for the “strat guys” - I would appreciate some answers. Can we be certain that the connection or link will fully engage? With the tropospheric PV having undergone at least some disruption over a period of at least several weeks, is this likely to interfere with the normal “coupling” process?  What is the time lag for any impact? If, as possibly indicated, any uptick above proves to be very temporary and is reversed, can the link be broken again just as quickly or is it more a case of a longer lasting legacy once the process initiated?

I have also noted that there has been considerable uncertainty with the extent of some of the brief early/mid-winter warmings which have occurred and those which have been inconsistently modelled. There has been talk of a possible fully blown SSW event. I know that the latter are actually rather rarer than some might believe and are often confused with the final winter warming event. Furthermore, quite often the downwelling is interrupted or does not propagate fully to the surface. On other occasions it occurs in several stages. The impacts can be very unpredictable too. HLB patterns will be established but the displaced deeper cold from the Arctic does not always get into Western Europe, let alone the UK. The very nature of HLBs is that they usually establish “meridional” patterns and one can just as easily be on the milder (southerly) side as the colder (northerly side).  I believe that there is rather too much hype regarding SSW events and, perhaps, too many coldies’ hopes are placed on them occurring at all and in being the right place. As I have said in several recent posts, far more colder patterns have been established with very little or no assistance at all from the stratosphere. SSWs can occur when a colder pattern has already been in place and then interfere with that pattern. This could either enhance or remove the cold from any particular location.

I take the view right now, that we should be patient and wait to see how the current uncertainties are resolved and whether we might still achieve a cold(er) set–up. If we do end up with a rather mobile, zonal pattern producing a more prolonged period of unsettled mild(er) weather, then we can still look forward to another bite at the cherry with a “possible” SSW impacting later on. In any event, as some have already said, even this more zonal spell, may well be punctuated with some colder interludes and I will be painting a more positive picture for coldies towards the end of this post!

4. The MJO

There has been a lot of confusion and uncertainty regarding the MJO. There have been conflicting reports concerning the exact phase that the MJO has been in as well as the level of amplitude. There has been some suggestion that the MJO signals have been masked by other signals like those associated with the ENSO impacts. Much the same uncertainties continue with the current predictions for the next week or two. Some say that there are occasions when the MJO is not a particularly relevant factor but at other times it has a far greater influence. I noted one of @nick sussex’s recent posts with comments regarding a NOAA statement where they felt that the next cycle of the MJO should see it becoming far more active and influential.

The MJO (if the latest predictive charts are correct) has been emerging from the Circle of Death and moving into phase 2 which I believe can assist with MLB (not HLB) – more on that shortly. It should continue to grow in amplitude as it moves onto phase 3. It might then reach the key phases of 7, 8 and 1 towards the latter part of January which favour or assist with achieving greater HLB patterns.

There is a time lag of a week or two between phases and changes in the MJO and when they start to impact. That would be around early to mid-January for greater MLB patterns and around late January or early February for greater HLB patterns. Given the existing uncertainties, we cannot be sure what we have just seen while the MJO should have recently been in phases 8 and 1. I’ve seen several comments that it was not entirely lifeless whilst in those phases. In fact, it might explain why we have been seeing rather more amplitude in some of the recent model output for the next couple of weeks compared to what was shown just prior to that (when the change to a longer milder/zonal spell was first indicated) just a few days ago.

In a recent post I also suggested (as several others did) that there might still be an embedded amplitude signature remaining in the lower layers of the atmosphere following the disruption to the tropospheric PV. This combined with any residual MJO impacts might be at least one reason why the models have tended to move away from a really flat pattern.

5. Other Impacts

There are various other factors which may well be adding to the current uncertainties. I’ll list a few but will not go into any detail now. The recent solar bursts as well as moving towards the low point of the sun spot cycle – I think it’ll be at its lowest in 18 months to 2 years’ time and this may have even greater impacts in the 2019/20 winter, if not before then. The “Maunder Minimum” – a 300 to 350 year cycle with an extended period of little or no sun spot activity for around 30 to 60 years is also expected to impact from around 2020 onwards. This cycle has been associated with much more frequent severe winters (like those in what became known as “The Little Ice Age” from 1650 to 1715). Whether we might see similar impacts this time around is still far from certain, especially when linked to other changes, like those associated with global warming. Whether there might be some earlier impacts (this winter) just ahead of these cycles reaching their minimum positions is very uncertain.

Another impact might well be linked to almost record low Arctic sea ice build-up for this time of the year as well as the quite exceptional anomalously high sea surface temperatures there. This and the very high Asian snow cover has been associated with very weak and disrupted tropospheric PVs and we have just seen those to some extent (see above and below).

Now, let’s keep in mind some of these considerations and uncertainties when I look at some of the current model output.

CROSS-MODEL ANALYSIS:

This time I want to focus on three time periods. These are day 5, day 10 and day 16 charts. As I always say, although the more distant FI charts are highly unlikely to verify, we can examine the various evolutions and look for any possible trends and changes and see how the models handle these.

I shall use today’s 12z (where available) and 18z output (with times adjusted for greater consistency).

I start with the current chart for 1300 December 28th:

          ECM 12z T+0

 

The current chart shows that the WAA into the Arctic from the Pacific/Alaskan side, that had been shown on all the models but (mostly) only for the last few days, verifies with HP building across the far side of the Arctic. This has disrupted the PV but it has also strengthened to some degree. I still see some posters referring to a really strong PV but they only show a "Europe view" chart. Looking at the whole of the Arctic profile tells rather a different story.

Day 5 charts for 1300 January 2nd:

       UKMO 12z T+120                    ECM 12z T+120                     GFS 18z T+114                      GEM 12z T+120  

                

 

      NAVGEM 12z T+120               JMA 12z T+120               GEFS Control 18z T+114        GEFS mean 18z T+114

                

There are already some minor differences between the models at day 5. They all show that the PV has strengthened to some extent and is a little more organised. They still show it under some degree of attack. There is HP extending from the Alaskan side, ridging through the far side of the Arctic and linking to strong HP over central Russia and northern Asia.  Unlike on a number of recent runs, GEM has now joined the party and is fractionally more amplified with slightly stronger HPs. The GEFS mean can be misleading as it averages out all 20 of the ensembles, plus the control run and the GFS operational run and needs to be examined with caution. At this shorter range it's very similar to the control run. 

Here is the GEFS 18z T+114 Panel with the ensemble suite:      

This shows only modest variations at day 5. Some have a slightly stronger and more organised PV but others show it remaining under attack, more so from the Russian side.

Day 10 charts for 1300 January 7th (note that UKMO does not go beyond day 7 and NAVGEM does not go beyond day 7/8):

       ECM 12z T+240                      GFS 18z T+234                       GEM 12z T+240

           

 

 JMA 27.12.17 12z T+264     GEFS Control 18z T+240         GEFS mean 18z T+240

           

Some interesting changes by day 10 with all the models showing at least some greater disruption to the PV. The ECM shows another push of WAA from the Alaskan side with HP rebuilding across the Arctic, with further HP building in from the Russian side. There is a col over the Pole. It shows a slack LP trough extending over the UK.  GFS on the one hand shows slightly more extensive LP in the Arctic but the PV is under renewed attack and there is greater amplification. HP is starting to build over Scandinavia and LP further south to the east of the UK . The GEM is similar but with the PV under even greater attack. JMA has rather less WAA and slightly more extensive LP over the Arctic but this is fairly weak. The GEFS control run shows a slightly stronger PV but it's very disrupted and closer to splitting again. Even the mean shows some quite high pressure ridging in from Alaskan towards the Pole.

Here is the GEFS 18z T+240 Panel with the ensemble suite:      

Just about all the members show the PV under considerable attack from various angles with several getting close to split again. The PV  has varying degrees of strength.

Day 16 charts for 1900 January 13th (note that only GFS and GEFS go beyond day 11):

         GFS 18z T+384             GEFS Control 18z T+384         GEFS mean 18z T+384

           

The GFS operational run shows a strong lobe of the PV extending down to Greenland and Iceland. There is now a trace of amplification in the Atlantic and a strong rise in heights to the north-east. The control run has a less strong PV with a belt of HP extending from the Russian, through the Pole and down across and beyond Svalbard.  

Here is the GEFS 18z T+384 Panel with the ensemble suite:     

Many more of the ensemble members are showing the PV under intense pressure again with several close to splitting and one fully split. One has a strong HP ridging north from the UK towards the Arctic and Greenland. This is a classic evolution to a warm Greenland cut-off HP. Many more members (about half) have a strong rise of pressure to our north-east with at least a couple of Scandinavian HPs evolving.

Overall, there are strong signs that the models (up to the mid-term) and the GFS (into FI) are starting to drop the idea of a progressively strengthening PV. In fact the reverse applies with the PV coming under considerable further attacks from all sides. Another developing theme is the steady rise in heights to our north-east indicating a possible evolution to a Scandinavian HP and eventually an easterly. Now, is the GFS correctly sniffing out this evolution or is it going down the wrong path and we'll see a strong swing away before to long? There is definitely some interest for coldies. Even the zonal patterns generally have some colder polar maritime air continuing to push in behind each LP as it passes through. One way or another it doesn't look like we are going to see any prolonged mild weather. For the time being brief colder interludes with some frost and snow (in favoured spots) looks to be on the cards. If the PV continues to be disrupted there remains at least a possibility of a change to a more prolonged cold spell later in January. i shall keep this situation carefully monitored and provide a comprehensive update by early next week                                                                                    

Finally, one of the few absolute certainties, regarding the shorter term outlook, is that the New Year begins at midnight on Monday morning! I’m not sure if I’ll have time to make another post before then, so let me take this opportunity to wish everyone a very happy, healthy and prosperous 2018.

Edited December 29, 2017 by Guest
Correct typos and check charts

[Weather-history]

2 hours ago, joggs said:

Absolutely awful for coldie.

If you are expecting sub zero and -20c frosts but actually that suggests to me a lot of polar maritime outbreaks, so wintry opportunities, the more so further north and west you go.

 

[Ali1977]

A very good 00z run for coldies, day 7- 12 take a northerly into an easterly and although uppers are around -6c to -8c this would be close to ice days - especially day 10 in a slackish easterly flow, with severe frosts.

Edit - some support in the ENS for this including sliders and Easterlies - although in varying forms - I imagine a pretty cold suite around the 7-12 day mark as mentioned regards the Op.

Day 10 on the GEM also supporting the above, if the ECM also jumps on board I'll be starting to think the 2nd week of Jan is game on for a "decent " cold spell.

Edited December 29, 2017 by Ali1977

[feb1991blizzard]

Plenty of undercutting / sliders going on in the GEFS suite - big upgrade - an absolute stonker.

[Ali1977]

4 minutes ago, feb1991blizzard said:

Plenty of undercutting / sliders going on in the GEFS suite - big upgrade - an absolute stonker.

P20 looks pretty nice ?

[knocker]

Today some heavy rain with strong winds across England and Wales , particularly in the north and southern Scotland, where the rain is liable to fall as snow, particularly on the high ground. Clearer ib the south later but some wintry showers perhaps thundery. Overnight another frontal system tracks quickly through England and Wales bringing more rain and quite windy for a time whilst further north it remains clearer with frost as temps dip.

After some brief ridging on Saturday another intense little low which formed off the eastern seaboard has 'bombed' quickly north east on the jet and is 966mb over N. Ireland by Sunday 00. This will bring heavy rain to the north, and a fair whack of snow on the higher ground in Scotland as it quickly tracks into the North Sea.

But with the upper trough now centred to the NE/E other perturbations slip south east in the circulation after the passage of this low into Scandinavia and one such perhaps brings more snow to the Scottish mountains on Monday whilst at the same time another wave has tracked south east around a transient ridge en route to France which may just impact Cornwall.

Mean while another low that originated off the south east seaboard 48 hours earlier has tracked north east and deepened in mid Atlantic and by 12 Tuesday is 964mb SSW of Iceland with it's associated front is lying across western parts of the UK accompanied by more rain and strong gales force winds as it quickly traverses the UK. But to complicate matters another wave has formed on the front that impacts Scotland bringing more snow the Highlands.

By midday Wednesday the UK finds itself at the coal face of a quite complex pattern to the west. Essentially a cold trough down the eastern half of N. America with colder air in the west and north west Atlantic with a strong thermal gradient dividing it from the warmer air to the south west with the jet indicating this running smack bang over the UK. Ergo as can readily be seen on the surface analysis for that time the UK is at the sharp end of two 'feeds', and never the twain shall meet, so to speak. Thus there is a low to the NW of Scotland introducing more snow and an active front west of southern Ireland about to bring rain to the south west.

Who will win the battle of the airmasses.? Well there is a lot of energy being pumped north east and that low 999mb that can be seen on the front on the above chart tracks rapidly north east and deepens to be 972mb close to the Western Isles by 1800 on Thursday bringing more rain to England and Wales and gales and snow in the north, But as it tracks into the North Sea matters are further complicated by a tempory surge of the Azores HP to the west which forces the low south veering the wind northerly  over the UK, Best left here.

 

[northwestsnow]

39 minutes ago, feb1991blizzard said:

Plenty of undercutting / sliders going on in the GEFS suite - big upgrade - an absolute stonker.

Yes its a cold suite longer term!!

Goes against all the background signals/telecommunications tho so im suspicious..

[Spah1]

17 minutes ago, knocker said:

Today some heavy rain with strong winds across England and Wales , particularly in the north and southern Scotland, where the rain is liable to fall as snow, particularly on the high ground. Clearer ib the south later but some wintry showers perhaps thundery. Overnight another frontal system tracks quickly through England and Wales bringing more rain and quite windy for a time whilst further north it remains clearer with frost as temps dip.

After some brief ridging on Saturday another intense little low which formed off the eastern seaboard has 'bombed' quickly north east on the jet and is 966mb over N. Ireland by Sunday 00. This will bring heavy rain to the north, and a fair whack of snow on the higher ground in Scotland as it quickly tracks into the North Sea.

But with the upper trough now centred to the NE/E other perturbations slip south east in the circulation after the passage of this low into Scandinavia and one such perhaps brings more snow to the Scottish mountains on Monday whilst at the same time another wave has tracked south east around a transient ridge en route to France which may just impact Cornwall.

Mean while another low that originated off the south east seaboard 48 hours earlier has tracked north east and deepened in mid Atlantic and by 12 Tuesday is 964mb SSW of Iceland with it's associated front is lying across western parts of the UK accompanied by more rain and strong gales force winds as it quickly traverses the UK. But to complicate matters another wave has formed on the front that impacts Scotland bringing more snow the Highlands.

By midday Wednesday the UK finds itself at the coal face of a quite complex pattern to the west. Essentially a cold trough down the eastern half of N. America with colder air in the west and north west Atlantic with a strong thermal gradient dividing it from the warmer air to the south west with the jet indicating this running smack bang over the UK. Ergo as can readily be seen on the surface analysis for that time the UK is at the sharp end of two 'feeds', and never the twain shall meet, so to speak. Thus there is a low to the NW of Scotland introducing more snow and an active front west of southern Ireland about to bring rain to the south west.

Who will win the battle of the airmasses.? Well there is a lot of energy being pumped north east and that low 999mb that can be seen on the front on the above chart tracks rapidly north east and deepens to be 972mb close to the Western Isles by 1800 on Thursday bringing more rain to England and Wales and gales and snow in the north, But as it tracks into the North Sea matters are further complicated by a tempory surge of the Azores HP to the west which forces the low south veering the wind northerly  over the UK, Best left here.

 

Knocker you’re a machine. 

Do you never sleep? 

Great post as always. 

[Duane S.]

38 minutes ago, northwestsnow said:

Yes its a cold suite longer term!!

Goes against all the background signals/telecommunications tho so im suspicious..

No surprise, it's been trending this way for days.

I'm not saying, at this stage, it's necessarily going to end up being more correct than the more progressive OPs of late though.

Just that last night's 18z missed delivering by smidgen and only needed a small tweak upstream mid term to do so. Which is what we've essentially got on the 00z here.

[Iceberg]

3 minutes ago, s4lancia said:

No surprise, it's been trending this way for days.

I'm not saying, at this stage, it's necessarily going to end up being more correct than the more progressive OPs of late though.

Just that last night's 18z missed delivering by smidgen and only needed a small tweak upstream mid term to do so. Which is what we've essentially got on the 00z here.

Completely agree. The models particularly the ens and eps have been hinting at the this. The trend has been the angle of energy thru the uk into France and then the med by t240. With such an angle a cold spell is always possible. 

Gfs has the waa to create a high pressure to our ne. Ec first quite fry there. 

There is also a stalling of the energy over the nw Atlantic. Which is consistent. 

[knocker]

The ecm haws been pushing the nor'easter storm for a couple of runs now which helps promulgate the mid Atlantic ridge late on otherwise no great surprises in the run, remaining unsettled with temps varying around the average but dipping below towards the end. The key factors are wind and rain.

Edited December 29, 2017 by knocker

[mulzy]

The 7-10 day period is definitely beginning to show more interest.

Day 10 GFS - a little of higher heights to our north (akin to Jan 2013 perhaps?)

Day 10 GEM - a shallow northerly flow - very much slider territory going forward.

Day 10 ECM - slider - probably wrong side of marginal for most.

Day 10 ECM eps mean - much better than the op - shows a wedge of heights to our north / north-east.  Fairly sure we will have a significant cluster showing a Scandi high at this juncture.

Health warning - these are day 10 charts but the trend is our friend here!

 

[Nick F]

Yep, the GFS op not without credibly large enough support from ens members for the ridge to build NE near the north and west of the UK and eventually leading to a Scandi high

Is the ECM high res too progressive in breaking down the Atlantic ridge? Could be, but we'll need to see where the det. sits with the ensemble spread.

[Man With Beard]

ECM mean chart has a weak Scandi High and Italian low at T240. Well be interesting to see how this is broken down in the clusters later. 

Interesting to see how the period 6-8 Jan is working out on the op runs. The GFS sets up a minor easterly, the GEM keeps a northerly and the ECM op throws in more southerly tracking lows. All with wintry potential, especially further north. In fact, for Scotland, there could be several snow events in the next 10 days in addition to the one today, given the negative tilt on so many lows.

Until then, as Knocker states, lots of wind everywhere and rain for areas south of the M62, with flooding potential particularly in the SW. 

[carinthian]

22 hours ago, carinthian said:

Yes, not without interest this chart at t240 from ECM. For some reason the UK has been on the right side of the Polar Trough for much of the early winter season. Maybe if the dig south of the Polar Trough shown above can be maintained and the upper heights strengthen over Scandinavia as NF mentioned there is hope of a more prolonged colder period for NW Europe rather than the transient cold into the British Isles.  GEM model sort supports this set up and looking at the extended UKMO at 168t , that maybe going along these lines. If we can get this set up holding for a few days , maybe we can hopefully stop the Atlantic zonal flow renewal during the Mid Winter period.  Certainly no cold for SE Europe / SW Russia so far this winter looking at this chart.

C

The American Models pick up the trend of yesterdays ECM to strengthen the upper heights over Scandinavia at t240. Maybe the block can build a more prolonged colder spell for much of Europe. Certainly, the UK is  having a more favourable chance than many in lowland Europe so far this year for snow albeit marginal and transient. Hopefully the chart below comes off and you will see cold spell extending !  This morning ECM not showing the heights building NE on their latest run but looks cold side for many but not as robust as the GFS/GEM model out at 240t. Anyway interesting weather for you guys so far this winter and good chart viewing.

 C

Edited December 29, 2017 by carinthian

[knocker]

Not that one can take too much notice of these but to get the idea the gfs precipitation for ten days.

[knocker]

The ext EPS mean 10-15 anomaly has the main player the Canadian vortex and the negatively tilted trough Iceland/UK eastern Mediterranean. Another key component is the ridging in the eastern Arctic all of this resulting in a split upper flow in the eastern Atlantic with one arm swinging NE and the other SW with the UK at the coal face. Without wishing to sound obvious the det,runs will need to sort which will be the predominate track for systems approaching the UK. All set up to go a clustering.

I will say one thing. It's been a very wild two or three hours down here this morning with 50mph gusts and a thunderstorm thrown in.

Edited December 29, 2017 by knocker