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Model output discussion - winter proper underway

Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

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9 minutes ago, bluearmy said:

Awaiting the eps clusters but the spreads at day 10 reveal an amplification off the eastern seaboard - wonder what the percentage will be ??

 

Not sure, but when the mean shows it that strongly, one suspects almost all must be going for it?

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51 minutes ago, TEITS said:

Having read some of the posts from last night and this morning, if you don't mind me saying some are in denial. No evidence as mentioned last night of the jet continuing to run NW-SE. Little evidence of any significant height rises to our NE. The return of a milder pattern was obvious to me as I mentioned a few days ago.

What we are likely to see is a rather typical UK winter weather pattern of a flat jetstream with low pressure systems tracking NE to the N of the UK. Milder SW,lys with the weather more settled further S and rather more unsettled and windy for Scotland.

If we do see pressure rising then it is more likely to occur over the UK bringing settled conditions and cold nights. The last thing I see is any cold, snowy E,ly whilst heights remain low to our NW/N.

Sadly I would be amazed if any of the above changed before xmas. My punt is a dry, settled Xmas but at least we should wake up to frost which is better than wind/rain.

I'm certainly not in denial, i've been banging on about the increasing Atlantic influence from the GEFS mean for days but it's been conveniently swept under the carpet during the cold frenzy.

Edited by Frosty.
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16 minutes ago, jvenge said:

Not sure, but when the mean shows it that strongly, one suspects almost all must be going for it?

This says ‘uncertain’ to our west by mid next week as the array of clusters past day 10 has illustrated recently 

A4ED7EAB-D584-48DB-8131-37CCD8642B2E.thumb.jpeg.5c6fc930bc29507b338f928ff6e9ac2b.jpeg

Edited by bluearmy
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1 minute ago, Draig Goch said:

I'm also wondering if the rain moving into the west and heading east later tomorrow might have snow along the front edge if it stays this cold. If it does it would be another chance for those in South Wales & southern England who missed the snow to get at least some temporary accumulations before turning back to rain. Fingers crossed. 

I feel like the models are underestimating the snow on the leading edge of the front, because there's a lot of surface cold around currently. For instance, high of -4C here yesterday, low of -8C last night, and it expect it to be about the same tonight and tomorrow too before the front moves in. 

Maybe some sort of chance for us up North who have missed it all recently, we'll see...

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12 minutes ago, bluearmy said:

This says ‘uncertain’ to our west as the array of clusters past day 10 has illustrated recently 

A4ED7EAB-D584-48DB-8131-37CCD8642B2E.thumb.jpeg.5c6fc930bc29507b338f928ff6e9ac2b.jpeg

Yes, the uncertainty appears to be in the interaction with the ridge and the exact placement of the Canadian vortex, rather than the actual overall theme. This can be the difference between double digit temperatures and perhaps a chilly polar maritime/colder zonal flow, though...

I'm personally a little suspicious that so many of the ECM EPS handle the vortex that way and the GEFS too, even in the furthest reaches. It's the first thing I'm looking at on the EPS and GEFS each run now.

Edited by jvenge

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Just as a side issue from the Amplification (or none as we head through xmas), I was having a debate the other day about the changes made to ensembles and that I had noticed that more amplified members seem to pop up in the first 10 GEFS pertubations (particularly wrt easterlies), 6z is a classic example.

gensnh-5-1-384_yje3.png

gensnh-6-1-384_opg3.png

gensnh-8-1-384_ema6.png

 

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1 hour ago, bluearmy said:

Awaiting the eps clusters but the spreads at day 10 reveal an amplification off the eastern seaboard - wonder what the percentage will be ??

as the North Pacific ridge goes up again and the Canadian trough digs south again in response , we are seeing the jet strongly across the Atlantic (as a consequence of the temporary pull back of the Pacific ridge) with no Atlantic ridging evident - I think it’s incorrect to just assume this will verify. The atmosphere has been predisposed to amplify to our west thus far and it may well do so again once the upstream trough digs.

of course this is not currently the favoured route forward approaching xmas with a sinking zonal flow more likely as the Azores ridge sinks away and pulls back further south. 

I think this is a very reasonable stance to take today. Much will become clear as we head through this week... but for now timing of the next phase of winter is up for grabs.

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1 hour ago, Frosty. said:

I'm certainly not in denial, i've been banging on about the increasing Atlantic influence from the GEFS mean for days but it's been conveniently swept under the carpet during the cold frenzy.

Agreed Frosty - I think pretty much everyone has been saying a period of westerly influence through mid December was likely. What we have just experienced (though not everyone saw snow!!) was a rather unexpected appetiser to winter.... and the teleconnective guidance has been to look at the impact of the next MJO cycle, now firmly underway, sitting on top of a sustained AAM budget, with appropriate lag taken into account. Late December into January was always the call for proper cold to arrive... if it arrives.

The slight addendum to that is that we have experienced so much amplification recently (look at the winter storm in southern US... biggest in a hatful of years) that some suggestion of sustained mid atlantic ridge influence has become worth chewing over. BA has pointed to this well today - though a 17% temporary cluster isn't much to celebrate. However I would agree with him - flatter pattern for a while still likely but not absolutely guaranteed yet.

Still keenly awaiting the latest data from the pacific....

Edited by Catacol
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From the latest GFS run, heights remain over the pole beyond T240 and from history whilst they remain in that unusual locale, I have found that cold spells often pop into the forecast without much notice as they often struggle whilst heights remain oop North.

A bit of hopecasting, yes,  a bit of viewing experience yes, but I'm not ready to churn out the Vardy,  just yet.

S71211-120212.jpg

S71203-053627.jpg

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A Few very cold runs from the ens at the end of the GEFS 6z . Are take purb 5 😀 For Christmas Day . We can dream .  

IMG_0851.PNG

IMG_0852.PNG

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Well first real sign in the 15 Day ensembles of swinging back to colder, from less cold conditions toward the end of the month. 

ensemble-tt6-london.thumb.gif.c9aa6f9f143e01a3021abf9645895c67.gif

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May lead to nothing but the Atlantic pick up at the weekend doesn't look straightforward looking at the clusters from the latest gefs.

First of all a look at the 850hPa temps

viewimage.pbx?type=ens;date=20171211;tim

showing the mean rising around the 17th but the op staying cold along with a few other members.Looking at the jet stream patterns for that time

viewimage.pbx?type=ens;date=20171211;tim

a lot of splitting and signs of trough disruption around the UK with some energy leaking south.

The favoured evolution for week 2 is still for the flattening upstream to release enough Canadian energy to push the Atlantic through but maybe as we get closer the higher resolution of the operational runs may ease back on the amount of strength in the northern arm.

Just putting it out there for something to monitor over the next few runs.

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9 minutes ago, Purga said:

Well - don't despair too much folks, the GEFS 06z do show a cool down towards Christmas with some beautiful runs appearing.

Notice the improvement from 00z to 06z (to add to Karlos's post above).

image.thumb.png.8313d43428cf2eb04b44f1204006eea4.pngimage.thumb.png.c64a414ff319e7d2a3cdb8da095818b0.png

Who wouldn't love to wake up to a 1962/63 Christmas like this?

image.thumb.png.33c4bb825878b5b0750284360e5d6d41.png

image.thumb.png.1b49a77d081dd90c0321da0b2e1613fe.png

Obviously a very unlikely scenario but at least it has a few supporting runs.

:)

Agreed no 5 will do :santa-emoji:

gens-5-1-336_wje6.pnggens-5-0-348_ehv4.png

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A CROSS MODEL ANALYSIS - GOOD NEWS FOR COLDIES!

My word it continues to be very quiet on this thread. This is probably down to a number of factors - some still discussing the snow on their respective regional spreads, a few (of the usual suspects) starting to think that winter is nearly over, some feeling that it's a long way back to any more prolonged cold (quite wrongly in my opinion) and perhaps some taking a break after the frenzied activity over the last couple of weeks. We seem to be missing many of our regular contributors who analyse the model output. So, I feel that we need to call in the reserves until the troops return! I shall break off in preparing part 2 of my weekly report (which may be ready late this evening) and attempt to provide a cross model analysis. While I am writing this from a sleety Exmouth, the 6z runs are rolling out and I will include this and the 0z runs from the other models. 

Yesterday (on page 7) I took a rare excursion into deep FI in order to show that most of the GEFS ensembles (from yesterday's 6z) were showing the PNA going strongly positive again with HP building strongly in the Arctic (some runs maintained it throughout) with strong signs of recovering amplification of the mid-Atlantic ridge and heights also building to our north-east. This was entirely consistent with what our experienced teleconnection posters have been telling us. Nothing seems to have changed in the following 12z and 0z runs. It has also been stated that these changes will follow a period of milder weather. While things can change later on, the main uncertainty was more to do with the timing of the change and the length of the milder interlude. The recent thinking was a change back to the much more blocked regime from around or shortly after Christmas time. This might be a few days sooner or later. I stressed that we need to be patient in searching for this evolution. The models are likely to continue to struggle with this broader pattern change and we can expect to see some big swings from run to run for the following week or so at least. I will be looking for the early signs of this evolution (much better than some seem to realise) and a trend developing. There will be some critical updates to come from the likes of @Tamara, @Glacier Point, @chionomaniac, @Catacol and others who follow and interpret the teleconnections.

Right, that's enough on the post Christmas period. The rest of this post will focus on the shorter term. There continues to be a little uncertainty on how long the current cold spell will last. After a hard frost tonight (severe over the snow fields) it looks like it will be less cold mid-week before another northerly moves in later in the week and into this weekend (more of less the 7th weekend in a row) although winds are already backing into the west by Sunday. Up to this point, there is broad agreement with all the models showing a northerly on Saturday as can be seen in the 5 day charts below. This Arctic outbreak would appear to be less potent that the recent one. The majority of model runs have been showing a change to a flatter westerly pattern with less cold or rather milder conditions spreading in. There have been variations on this theme with some runs showing a slightly north of west flow at times with more polar maritime air in the mix and rather cold conditions while others go for a generally milder Atlantic flow. The odd run continued to show colder conditions persisting. So, lets have a look at two periods for a cross model analysis with time adjustments to show an accurate comparison.  

 5 days out at 0100 on Saturday, December 16th:   

                   UKMO 0z T+120                                         ECM 0z T+120                                       GFS 6z T+114                                        GEFS 6z T+114             

     UN120-21.GIF        ECH1-120.GIF        gfsnh-0-114.png?6?6         gensnh-0-1-114.png

 

                    GEM 0z T+120                                      NAVGEM  6z T+114                           JMA 12z (Dec 10th) T+132

    gemnh-0-120.png         navgemnh-0-114.png         JN132-21.GIF

 

10 days out at 0100 on Thursday, December 21st (note that UKMO and NAVGEM do not publish charts for this far out and the D8+ JMA charts have not updated for several days):   

                    ECM 0z T+240                                       GFS 6z T+234                            GEFS 6z T+240 (12 hr gaps, nearest)              GEM 0z T+240 

    ECH1-240.GIF         gfsnh-0-234.png?6?6         gensnh-0-1-240.png        gemnh-0-240.png 

I strongly feel that this is a case of first appearances being quite misleading!  On their most recent runs, all the models have shown the northerly being replaced by less cold or milder westerlies (either just north or just south of a straight westerly). Some runs went through a wetter spell but other runs are much drier with HP much closer to the UK. I'll let others analyse the details through this D5 to D10 period as I'm really interested in how the period ends around D10. The ECM may show one of the milder T+240 charts (dry in the south and wetter in the north) but there are still some encouraging signs. The PNA is starting to go more positive and there is HP building across the Arctic again. The GFS, GEFS and GEM D10 charts all show a large belt of HP building across the country. With the latter two starting to show a Scandinavian HP developing. In fact GEM is the most progressive with the HP extending all the way from Siberia, through Russia, Scandinavia and linking up with the Atlantic HP. They even have lower heights appearing in central/northern Europe and signs of an easterly developing. Whether these three charts are too progressive or whether the ECM is a little behind the curve is not really relevant this far ahead. The trends are there and from a coldie's perspective this is exactly what I have been looking for.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

Part 2 of my weekly report will focus on European temperatures and what we might expect from an easterly, should it come to fruition.                             

Edited by Guest
Correct typos and check charts

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18 minutes ago, Dancerwithwings said:

Agreed no 5 will do :santa-emoji:

gens-5-1-336_wje6.pnggens-5-0-348_ehv4.png

With this set-up pretty much all of us in the UK would likely benefit at some stage - and no it wouldn't be sleety marginal stuff :D

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There's a few people in here being a bit quick to call "mild" in my opinion. Yes, it's likely to be less cold by the end of the week but going forward into next week it looks more like North-Westerlies will mostly dominate, it'll be wet with a fair amount of rain around as fronts push Eastwards but certainly nothing I'd call "mild", merely less cold than recent. 

Looking ahead, Tamara, GP etc have gone into detail about how heights towards Scandi look likely to develop towards the end of the month/early December and a few GFS ensembles are starting to pick up on that signal, too, not less, so is the control run.

Control

Control.thumb.png.1e37fc3648f84732273103d1998d278b.png

GEFS members

2.thumb.png.d37461a281c5deff2ecc7ab64e15d266.png5.thumb.png.8bc2f3805cd78d1df1bbef80307fa3b1.png6.thumb.png.92b7bc04900b8b85446ef348ee9f61a9.png

7.thumb.png.0f6e2679e185130b61b6c027d0c56392.png

Obviously they're in a minority at the moment, but there is slowly growing support for that signal within the suites including within the EC too with some members trending colder in the extended

EPS.thumb.gif.8f4fd004f6dd92550ba4fa0fad5d9930.gif

Plenty to be optimistic about, I can't see anything to suggest raging zonal winds and mild Atlantic muck as per the last 3-4 winters. Watch the Scandi height signal grow through this week and expect the OP runs to start throwing out increasingly erratic outputs in the mid-extended range, too.

The MJO is moving towards phase 8, 10+ days lag time puts us around Christmas, key dates for me at the moment are 24th - 29th December for blocking to begin developing.

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IMHO, there are some people who are just to quick to call? Then again there are those who interpret other posters musings as definitive predictions, and then turn round and complain whenever said 'predictions' fail to yield fruit...?:cray:

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It looks likely a very big and deep chunk of the PV is going to set up around Canada in the not too distant future....which could either mean gales and zonality (6z op) for us, or as some of the ensemble members show, cold can come about too. So much to play for!

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9 minutes ago, Ed Stone said:

IMHO, there are some people who are just to quick to call? Then again there are those who interpret other posters musings as definitive predictions, and then turn round and complain whenever said 'predictions' fail to yield fruit...?:cray:

In regards to my post above, definitely musings rather than predictions!! 

I would add that the EC clusters had a period at the end of November when they suggested a return to a flatter pattern around about now - we all know that did not happen!! So they could be wrong this time, too.

But if one took all of the model output today and studied it mathematically, they would not conclude an easterly to be the preferred option for Christmas. 

However, if someone things they can see signs of how the models might have got this wrong, that's a different matter - blooming good luck to you and I hope you are right :) 

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1 hour ago, Dancerwithwings said:

Agreed no 5 will do :santa-emoji:

gens-5-1-336_wje6.pnggens-5-0-348_ehv4.png

We can dream can't we:)..hopefully January will bring the Beast from the east:cold:

In the meantime, it's still cold, it will become less cold midweek and then a cold Northerly towards the end of this week..then next week and indeed christmas looks more Atlantic driven changeable / unsettled with some fine spells, mainly further south with temps swinging between colder and milder.

Edited by Frosty.
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