Model output discussion - winter proper underway

[nick sussex]

The shortwave shown at T168hrs is a spoiler and stops some  retrogression of the high to the sw.

This then cuts through the high at T192hrs and also impacts on that ridge to the north.

That small ridge could become important if the earlier shortwave is modelled differently. You're trying to remove the high to the sw and get its centre further west.

 

[feb1991blizzard]

27 minutes ago, blizzard81 said:

I've got a good feeling that we will see more colder ext ecm ensembles tonight ☺️ 

No change at 240 - lets se if anything can develop afterwards - id take a small increase in size of the scandi high cluster.

[Singularity]

Always an issue when the models are opting for the most efficient energy transfer possible and producing very large, intense storm systems as a result; they produce regionally flat-looking outcomes even when the broader-scale pattern is nicely amplified. It'd take a few days to push such a broad trough southeast and get back to a colder regime from the ECM day 10, but I question whether there will really be a large, deep trough to begin with; often enough I've seen these fail to come around, with the actual outcome featuring multiple smaller lows zipping across. In this case they'd do that and then merge with a trough to our NE, in a similar fashion to the past few days. 

It doesn't sound that exciting for southerners I know, but this is why the Scandinavian high signal is of interest longer-term (v. late Dec/early Jan) as it can potentially convert the polar maritime setup into a polar continental one, which works much better for those who've missed out so far this winter.

It's tricky I know to get the sense of balance having already come so close to low-level snow in the far-south this winter. Fact is, snow to below 200 m asl in that region is very rare indeed in December - as I know all too well! 

[blizzard81]

1 minute ago, feb1991blizzard said:

No change at 240 - lets se if anything can develop afterwards - id take a small increase in size of the scandi high cluster.

The means looks much better at 168 when compared to last night's 192 mean. 

[feb1991blizzard]

1 minute ago, blizzard81 said:

The means looks much better at 168 when compared to last night's 192 mean. 

[mulzy]

No change on the ext eps.  It's looking fairly bleak at the moment for coldies.

[bluearmy]

56 minutes ago, blizzard81 said:

I've got a good feeling that we will see more colder ext ecm ensembles tonight ☺️ 

There might be but it's not at all noticeable on the mean /anomoly 

[Chesil View]

30 minutes ago, Singularity said:

Always an issue when the models are opting for the most efficient energy transfer possible and producing very large, intense storm systems as a result; they produce regionally flat-looking outcomes even when the broader-scale pattern is nicely amplified. It'd take a few days to push such a broad trough southeast and get back to a colder regime from the ECM day 10, but I question whether there will really be a large, deep trough to begin with; often enough I've seen these fail to come around, with the actual outcome featuring multiple smaller lows zipping across. In this case they'd do that and then merge with a trough to our NE, in a similar fashion to the past few days. 

It doesn't sound that exciting for southerners I know, but this is why the Scandinavian high signal is of interest longer-term (v. late Dec/early Jan) as it can potentially convert the polar maritime setup into a polar continental one, which works much better for those who've missed out so far this winter.

It's tricky I know to get the sense of balance having already come so close to low-level snow in the far-south this winter. Fact is, snow to below 200 m asl in that region is very rare indeed in December - as I know all too well! 

Great post James. Especially the last couple of lines. I sometimes wonder whether we got our next twenty years worth of settling December snow all in one go back in 2010. Lol .  But of course back then we had heights to our north west ,north and northeast with encroaching lows from the west, which is why like you the possible hieght rises to our northeast suggested by GP and co are of so much interest to far south snow freaks like you and I

[offerman]

2 hours ago, blizzard81 said:

The azores high gets flattened more easily on the ecm which can only be good news imo. 

Someone mentioned it’s a permanent feature now as opposed to semi permanent . Have to agree that it does just seem to sit there for eternity. Life guarantees 

death  taxes and Azores High ....... :-0

[ANYWEATHER]

Evening All! So a milder spell of weather coming up, after this weekend , gfs and ecm hint of a change by Christmas , with a change to more stormy conditions with a mix of cold and mild

[Guest]

WHAT A HUGE AMOUNT OF NEGATIVITY ON HERE THIS EVENING - LET'S HAVE SOME BALANCE

Yes from a coldie's perspective "much" of the 12z output might seem rather less appealing compared to "some" of the recent runs BUT there have been some gross exaggerations on here and instant reaction to just one run or several consecutive runs (which is hardly a real trend yet). As @Tamara reminded us in her excellent post this afternoon (on page 49), there are some downside risks and uncertainties over the background signals and how they might play out but she emphasised how she thought that nobody can predict with any certainty (including the Met O*** and other well respected longer term models/forecasts) how the patterns might evolve moving into January. She highlighted these uncertainties but still was (I'm choosing my words carefully here) being cautiously optimistic regarding the changes to a colder pattern - please read her post carefully (or a second time if you already need reminding) to see how she expects continued volatility in the model output. (*** the Met O's most recent update for their 15-30 day outlook refers to this uncertainty but they are opting for mostly "below average" temps for at least the first half of January).

I was preparing my post on the 6z output early this afternoon while Tamara's update appeared (just ahead of mine on the same page 49). When I just read some of the comments on this thread earlier this evening, I assumed that I was going to see some pretty dreadful charts. I have just gone through them and I insist that they are really not too bad. The problem is that the broader changes (for the better) are still somewhere around 2 to 3 weeks away. We still cannot rule out a brief colder snap around Christmas but much of the output has consistently pointed towards a much milder spell from this Sunday/Monday until at least the run up to Christmas and possibly until towards the New Year. Yes disappointing for those hoping for a white Christmas holiday but certainly not a surprise. It's what follows that will be key.

Before I go on, I feel that I need to remind.a few posters (one of two of them being quite regular contributors) of a particular problem. When referring to broader pattern changes, making comments and drawing conclusions, it's very misleading to post the "Europe" view charts, we must see the "Northern Hemisphere" view charts to see the upstream pattern and changes. The Europe view charts are great for analysing the local patterns and anticipated weather in finer detail for the UK. 

I could pick on numerous examples but I'll highlight one that's cropped up a few times and that is references to the "PV looking so strong that we will never find a route back to cold from there" - or words to that effect..The period just prior to Christmas has been commented on. The climatological norm is for the PV and the jet stream to be at their strongest around and just after the winter solstice. Obviously this is often not the case but let's look at all of today's 12z model output for December 21st to put this into context. I'll also look at the actual charts for the last 4 winters at the same time:

                         UKMO                                                      ECM                                                          GFS                                                     GEM                 

                          

 

                       NAVGEM                                                    JMA                                               GEFS Control                                         GEFS Mean

 

                               

Almost all these charts do show an uptick in the PV to varying extents but please have a closer look at them. Most of them have varying amounts of HP usually close to or over the Pole and still signs of a marginally positive but weaker PNA than recently. Now the likes of Tamara, GP and Catacol, amongst others, have indicated that there'll be a weakening in the PNA (possibly negative for a short period), a breakdown in the Atlantic ridge and the AO going positive for a while (ie: hardly any HLB and much less intense HPs up there or much more LP). This period is expected to allow the strengthening in the PV and the jet stream (I'll cover the jet in another post over the weekend) prior to a likely (but not certain) strengthening of the PNA, probable re-amplification, hopefully on our side of the Arctic and in the mid-Atlantic again and may be building heights to our north-east. All this might evolve towards the end of the year or into early January. So, these Dec 21st charts are somewhere close to the early to middle part of the degeneration prior to the later recovery.

When I read some of the comments regarding the GEFS charts and the ensembles, I was expecting even worse news but I have examined the whole run and various perturbations and again they are not too bad and only a slight downgrade (at worst) on the 12z run (which I covered comprehensively in my post on page 49 this afternoon). The control and mean charts are shown above. The mean chart can be confusing and frequently leads to misinterpretations. It is an average of all 20 perturbations plus the control and op runs. The 12z mean chart is actually better than most of the other models' charts. Just focus on it for a while. There is still a +PNA and HP across the Arctic. This demonstrates that there must be some ensemble charts which have lower pressure and some with higher pressure. Similarly with the bands of LP, this shows that there must be some ensemble members with more intense/widespread LP and others with less LP of even high pressure in that vicinity. Out of the 20 perturbations I have picked four examples that show the strongest PV:

               GEFS Perturbation 3                            GEFS Perturbation  5                           GEFS Perturbation 12                         GEFS Perturbation 17

                          

The good news as far as I'm concerned is that it was a real struggle to find any charts with a really strong PV amongst the ensemble members. Pert. 3 is the only one where the PNA is broadly negative but there is still HP around the Pole. Pert. 5 has a string of LPs crossing the Atlantic on their path through Iceland.  Pert. 12 has the most intense LPs but there is +PNA and the flow is far weaker around the Pole and on the other side of the Arctic  Pert. 17 also has some nasty looking LPs but a +PNA and HP across the Pole. All four of these charts would look far worse than they actually are in the "Europe" view!!!

Now let's compare these charts to those for the same day in the last four winters using the NCEP Re-Analysis facility on Meteoceil:

                   Dec 21st 2016                                     Dec 21st 2015                                         Dec 21st 2014                                        Dec 21st 2013    

                             

Now most of us will remember last winter. A generally very blocked pattern from November right through to March but mostly MLB with only brief colder spells but also very little full on zonal periods. The forecast for the third week of December onwards looked bad briefly and the models suggested an extended stormy period but after a week the pattern stalled and petered out very quickly with a return to more MLB. Despite this, the PV on the Dec 21st 2016 chart looks better formed and at least as strong as on any of the worst charts above (for this year). The 2015 chart is very similar and note the lack of any HP in the entire wider Arctic region. The PV was not as strong in 2014 and it was only moderately strong in 2013. 

Even if we did see a raging PV with the jet stream powering through, the pattern can change incredible quickly. If there was a sudden uptick in the background signals again, renewed amplification could rapidly disrupt the PV. As several posters (including me) have said a change to a cold pattern can almost come out of the blue. One of the best example being this:

                Dec 21st 1962                                         Dec 23rd 1962                                       Dec 24th 1962                                       Dec 27th 1962  

                        

Now I know that several posters keep criticising other members for using analogue charts and it's important not to mislead anyone but they do have their uses. Here, I'm simply illustrating how a rapid change of pattern can occur from a fairly dreadful looking set up into something special for coldies. I'd love to a post on the background signal for that winter!

Overall I'm saying that things may get worse before they get better but at this stage there is nothing to be overly concerned about. Let's keep looking for the "recovery" signals and not exaggerate the poorness of the output before our eyes right now. Expect some wild swings in the next few runs. 

Edited December 15, 2017 by Guest
Correct typos and check charts

[Fourty Point Three Degrees]

I even said a few posts back that the Atlantic will come crashing in sooner or later, todays 12z confirms that even models are picking up on the trend. Even the CFS has been showing Atlantic domination on very much of its long range runs lately with some runs showing complete domination right through to mid January. The dream for a white Christmas is looking likely to continue

[Man With Beard]

1 hour ago, mulzy said:

No change on the ext eps.  It's looking fairly bleak at the moment for coldies.

By D15, perhaps 3 out of 51 ECM ensemble members giving a realistic shot at cold. The rest have a classic Canada to Scandinavia train of low pressures.

Still many colder options for the 22nd (though they all collapse by Christmas Day)

[cheshire snow]

@Bring Back1962-63

Again fantastic post,would be great if you could do a winter forecast or at the least a January LRF I am sure it would be a fantastic read

Again thanks for your detailed posts.

C.S

[feb1991blizzard]

4 minutes ago, Man With Beard said:

By D15, perhaps 3 out of 51 ECM ensemble members giving a realistic shot at cold. The rest have a classic Canada to Scandinavia train of low pressures.

Still many colder options for the 22nd (though they all collapse by Christmas Day)

Yes - looking like another false dawn now, I would fully expect the MO to change their wording tomorrow now, I expected it after the EC46 threw out a 'sidney' run the other day, but they were just probably waiting to confirm it.

[blizzard81]

I think we all need to keep cool heads right now even though the models tonight do not look very cool. I certainly wasn't expecting such a dismal set of ecm ext ens. Patience required again. Anything before new year would just be a bonus. 

[northwestsnow]

18Z looks a bit more amplified at 120 -

Lets see...

edit perhaps not- that horrid vortex ruins the hope of retrogression- too much energy yet again southern tip of Greenland...

 

Edited December 15, 2017 by northwestsnow

[blizzard81]

18z dangles the carrot! 

[carinthian]

5 minutes ago, northwestsnow said:

18Z looks a bit more amplified at 120 -

Lets see...

edit perhaps not- that horrid vortex ruins the hope of retrogression- too much energy yet again southern tip of Greenland...

 

American Navy model gives a bit of hope at 180t  with stronger ridging to Greenland high. Think 18z GFS run is starting to show this. Maybe a bit of a lifeline yet .

 C

[bluearmy]

24 minutes ago, feb1991blizzard said:

Yes - looking like another false dawn now, I would fully expect the MO to change their wording tomorrow now, I expected it after the EC46 threw out a 'sidney' run the other day, but they were just probably waiting to confirm it.

I guess it depends on their next glosea/mogreps run. Remember that the eps only go as far out as their further outlook and the 16-30 is the period beyond the eps. We don't see the ec 46 clusters so have no idea what the ens and anomolys are possibly hiding. 

I think too many fail to realise that the 16-30 is after the eps finish. 

[northwestsnow]

1 minute ago, carinthian said:

American Navy model gives a bit of hope at 180t  with stronger ridging to Greenland high. Think 18z GFS run is starting to show this. Maybe a bit of a lifeline yet .

 C

 

18Z is just about amplified enough to give snow showers into NE scotland by friday 22nd...

[ICE COLD]

I posted earlier that the cold spell that has just gone , leading up to it the pattern kept backing up further west . It's happening now and as a result lower 850s . 

Edited December 15, 2017 by ICE COLD
Added chart

[feb1991blizzard]

1 minute ago, bluearmy said:

I guess it depends on their next glosea/mogreps run. Remember that the eps only go as far out as their further outlook and the 16-30 is the period beyond the eps. We don't see the ec 46 clusters so have no idea what the ens and anomolys are possibly hiding. 

I think too many fail to realise that the 16-30 is after the eps finish. 

Totally agree but Man with Beard (and he gives balanced opinion of output) said that only 3 of 50 even LOOKED LIKE they MIGHT go on to deliver cold so I would suggest the MO would have not been expecting that when they wrote their outlook, plus they mentioned (or someone did) that they were saying SSW not out of the question, but that hasn't really progressed, plus I cant see the EPS 46 hiding anything special - One caveat I suppose battlegrounds aren't off the menu.

[northwestsnow]

Goodness me there is some absolutely frigid air spilling south through Canada on 18z

Thats just going to fuel an already angry Atlantic..

Just look at those 850s at 186hrs!!

[swfc]

1 minute ago, northwestsnow said:

Goodness me there is some absolutely frigid air spilling south through Canada on 18z

Thats just going to fuel an already angry Atlantic..

Just look at those 850s at 186hrs!!

Yep games up at that time period im afraid. Flat as a pancake! !!