Model output discussion 25th Jan - The final third of winter beckons..

[chris55]

DeBlit ensembles in the freezer from day 7

[Ali1977]

Can't post pictures but if the GFS run was right next Thurs could have a big snow event for some as the Atlantic hits the cold.  Close to a classic slider event.

[Ravelin]

1 minute ago, Ali1977 said:

Can't post pictures but if the GFS run was right next Thurs could have a big snow event for some as the Atlantic hits the cold.  Close to a classic slider event.

Here you go...

[Man With Beard]

2 minutes ago, Ali1977 said:

Can't post pictures but if the GFS run was right next Thurs could have a big snow event for some as the Atlantic hits the cold.  Close to a classic slider event.

Indeed. I'll help you out. Any 850s from a continental direction below freezing are in the game.

    

 

[chris55]

That's just what I was going to say Ali

you would think there is a decent risk of some place seeing some heavy frontal snow from this upcoming set up, the battleground scenario is a strong option at some point

[Singularity]

 

This is actually quite entertaining; at just 4 days range we see a more pronounced hang-back low but at the same time the high is some 4 mb or so stronger and positioned slightly further west, while a secondary low around the Italian trough moves further north and further helps to 'squeeze the isobars' and drive the deeply cold air west.

The following day sees the Atlantic trough orientated a bit more toward NW-SE rather than N-S with further helps the block to nose toward the UK.

Result by day 6 is this when comparing 00z on the left with 06z on the right;

 

It seems we really can't go assuming anything one way or the other with respect to the depth of cold reaching our shores.

Trough looks more willing to disrupt more effectively too... could we see a stunning outcome for the 7-10 day period?

Given the background signals, if we're ever going to get an 'end of the line' easterly to deliver a good blast, this is the time. Well, in a w-QBO type winter anyway!

Poised and with the Italy trough further north than recent runs. Looks like a classic fend-off in the making but this is GFS so nothing is certain  

[snowice]

4 minutes ago, chris55 said:

That's just what I was going to say Ali

you would think there is a decent risk of some place seeing some heavy frontal snow from this upcoming set up, the battleground scenario is a strong option at some point

IT always takes GFS several runs to get there, but every run there are small corrections west so i think it will be  Sunday before we know for sure!

[Cheshire Freeze]

7 minutes ago, chris55 said:

That's just what I was going to say Ali

you would think there is a decent risk of some place seeing some heavy frontal snow from this upcoming set up, the battleground scenario is a strong option at some point

Cue the Dan Corbett 'you see those blues oozing their way in from the east, rather like 'bumph' someone's dropped a tin of Dulux, bumping it's way against that ribbon of mild, rather like a piece of string being pulled from both sides'

[Ali1977]

All in all a much better run, even by 240 we still have the block in place, in a decent position and the cold 850s are gathering pace again....Great start to the day from the ECM and GFS.  We really need to see the METO on board before any confidence, but again they have a weekend of storms to concentrate on, but the BBC forecast did mention the cold Easterly next week.

[Zakos]

.             That really is a humongous block , I find it unlikely that Atlantic will break through, especially considering how stubborn blocking has been this winter. The key difference this time is the high is suitably far enough north, and we have low heights to the SE. Exciting times ahead, expect wild model swings, as small differences in this setup can have massive implications for UK weather. I have already seen snow, but I am looking forward to a potentially memorable cold spell this February. I won't be getting excited till a snow event is shown within 96 hours. The word "potential" has been used a lot on this thread this winter. However it can't be denied,as things stand, this event has the most potential for a memorable cold spell to occur from any output this winter.Thrilling model watching. 

Edited February 2, 2017 by Zakos

[johnholmes]

Re some comments about the low in the Med helping to reinforce the block. Don't wish for this pattern too much. They have a habit of pulling milder air north and then west with expected snow being rain as lower level air, say below 5000 ft, gets warmed out.

[Frosty.]

I agree it's thrilling stuff for snow starved coldies, hope the growing model trend from the 00z / 06z becomes reality!

Edited February 2, 2017 by Frosty.

[Ravelin]

11 minutes ago, Ali1977 said:

All in all a much better run, even by 240 we still have the block in place,

Yes, but into low res FI the GFS blasts the block away with a series of systems coming from the NW. Too far away to worry about but if it did happen the one consolation would probably be that the Scottish ski resorts might finally get enough snow to open.

[Summer Sun]

Met still going for something colder doesn't necessarily mean snow of course

 

[joggs]

7 minutes ago, Zakos said:

.             That really is a humongous block , I find it unlikely that Atlantic will break through, especially considering how stubborn blocking has been this winter. The key difference this time is the high is suitably far enough north, and we have low heights to the SE. Exciting times ahead, expect wild model swings, as small differences in this setup can have massive implications for UK weather. I have already seen snow, but I am looking forward to a potentially memorable cold spell this February. I won't be getting excited till a snow event is shown within 96 hours. The word "potential" has been used a lot on this thread this winter. However it can't be denied,as things stand, this event has the most potential for a memorable cold spell to occur from any output this winter.Thrilling model watching. 

You'd think the lower heights negatively tilted are going to go one way.......under.

[mb018538]

1 minute ago, Ravelin said:

Yes, but into low res FI the GFS blasts the block away with a series of systems coming from the NW. Too far away to worry about but if it did happen the one consolation would probably be that the Scottish ski resorts might finally get enough snow to open.

I wouldn't worry about anything further away than a week. A week ago we were shown this in FI for the 8th:


Now we're being shown this:


The models are always keen to return to zonal!

[Singularity]

3 minutes ago, johnholmes said:

Re some comments about the low in the Med helping to reinforce the block. Don't wish for this pattern too much. They have a habit of pulling milder air north and then west with expected snow being rain as lower level air, say below 5000 ft, gets warmed out.

The key is for a low that's strong enough to enhance the easterly flow, but is either not enough that the winds on the eastern flank are able to make much inroads into the cold air or - more effectively - has the wave axis aligned such that the warmer air hits a wall at the frontal boundary on on the north side the cold air powers west unheeded.

Looking at the 06z take on the trough disruption and my instinct is to say that there should be a low splitting away more readily into Europe when a stretched trough is hitting cold air of that magnitude. This sort of thing being why many frontal snow events in the past have ended up just clipping part of the UK having once been shown to power right in.

 

As for what happens after the transition to lower-res... well, this is why the model gets a lot of stick sometimes! Though I have to wonder where on earth the MJO forcing has gone in this and the 00z runs. It may be a symptom of the usual negative GLAAM bias which has the model seeing no jump into positive in response to the Pacific convective forcing, when there ought to be at least some - which would help to keep the vortex under pressure (it just reorganises and returns to the pole days 10-12 of the 06z run) and keep the westerlies restrained.

[ACCOUNT DELETED]

Not sure how likely this outcome will be, but this model suggests the very heavy rain moving up from SW England tomorrow, may turn to snow as it crosses Wales and then into Northern Ireland! 

[Buzz]

9 minutes ago, mb018538 said:

I wouldn't worry about anything further away than a week. A week ago we were shown this in FI for the 8th:


Now we're being shown this:


The models are always keen to return to zonal!

 

Which is exactly why people need to stop pinning their hopes on model output that's more than 72 hours ahead and very likely to change.

[bluearmy]

The gfs op 06z and gfsp 00z both power up the northern arm post through week 2 

hopefully just the model bias for mobility although a big cold block does generally need mobility from the west to deliver the snowfall most crave (via slider or undercut)

and john mentions the med low and warmer uppers conundrum - extremely valid, especially if the scandi ridge extends further se cutting off the prospect of the trough getting towards the eastern med. however, my view is always - highest risk = highest reward and given the likelihood that features tend to downgrade in intensity as verification approaches, I''ll take the chance for the time being !  

[DanDorsetUK]

Precipitation next Thursday night shows it could be a rather large frontal snow event. Still border line in the south though but a nudge further west wouldn't take much. 

[Snowman.]

22 minutes ago, Ravelin said:

Yes, but into low res FI the GFS blasts the block away with a series of systems coming from the NW. Too far away to worry about but if it did happen the one consolation would probably be that the Scottish ski resorts might finally get enough snow to open.

As soon as it hits low res, yes. However models especially the GFS greatly underestimate blocks to the NE and power up the jet to blow them away. Wouldn't take much notice as the pattern for the next 2 weeks is increasingly blocked. 

Lets get the block and potential cold in first before worrying about when it gets rid of it.

[Cheshire Freeze]

One thing to note, at 144 the GEFS mean is ever so slightly less cold with the Azores high pushed slightly further NE in towards the UK. I'm uncomfortable with its presence TBH as it will just encourage more jet energy to head N in the long run, increasing the likelihood of a sinking block. 

The GFS 6z low res is completely feasible unfortunately and may not be just 'model bias'

[johnholmes]

34 minutes ago, Singularity said:

 

The key is for a low that's strong enough to enhance the easterly flow, but is either not enough that the winds on the eastern flank are able to make much inroads into the cold air or - more effectively - has the wave axis aligned such that the warmer air hits a wall at the frontal boundary on on the north side the cold air powers west unheeded.

 

That is not really the answer, it is all about where the air on the eastern side of the low originates from, the stronger the flow in fact and the more likely, IF it originates from the Med area, that it will be rain or sleet at best.

[Guest]

IS THERE A LACK OF MODEL CONSENSUS OR NOT?

The models often struggle initially when a broad pattern change is predicted, especially in terms of timing and detail and will tend to fluctuate from run to run even into the more reliable period. Some are too progressive, others too slow to pick up on a new signal. The main driver this month is the extent, impacts and timing of the multiple warming events. While it is generally accepted that these events will have an impact, there are many "variables" which probably cannot be pinned down until they start to show up in the week 1 time frame. It is better to focus on the broad changes and not get bogged down with too much detail at this stage. As many on this thread (including me) have alluded to, it looks like we will see several attempts at establishing a colder pattern. The first stage is just getting underway with a stand off between the Atlantic and the European block seeming likely around D3 to D6 (Sunday to Wednesday) taking place over the UK.

Let's have a look at the D5 cross model charts for 0100 on Tuesday, February 7th:                          

                          GFS 0z                                                        ECM 0z                                                        UKMO 0z                                                   GEM 0z                                                      NAVGEM 0z

                           

                 GEFS ens mean 0z                               JMA 12z (Feb 1st) T+108                           Archive Jan 25th 1972  12z                        Archive Jan 26th 1972  0z

                

All the models show LP in the Atlantic to our west or north-west and HP building westwards from Russia into Scandinavia. There is considerable variation in the intensity of the main LP and whether it spawns secondaries and their track. With the Jet Stream taking an increasingly southerly track, most of the models show lower heights developing in the Mediterranean.  Any undercutting of the continental HP will assist in bringing the cold pool westwards. They all show an easterly flow developing but there is a question as to how far west it will get. Some recent model runs have shown it to envelope the UK, some just brush the east and south-east, some stopping in the North Sea and others holding it back in central Europe. This is the first phase and there is still considerable uncertainty over the short term evolution.  I have included an archive chart from late January 1972, which is one of the few "better" matches in terms of a sudden switch from Atlantic to continental influence. I produced a detailed post on this about 10 days ago with charts comparing that winter with this winter and the remarkable similarities - two very blocked winters with very little HLB and only brief cold snaps from November to late January. Please refer to page 299 of the December 29th winter model thread. Of course, using analogue charts should always be done with extreme caution and purely out of general interest as there are so many variable factors.

Now let's have a look at the D9 cross model charts for 0100 on Saturday, February 11th (note: UKMO and NAVGEM do not go that far out - so their latest available are shown instead): 

                           GFS 0z                                                       ECM 0z                                           UKMO 0z   Feb 8th T+144                                        GEM 0z                                       NAVGEM 0z  Feb 9th T+180

                   

                GEFS ens mean 0z                                  JMA 12z (Feb 1st) T+228                              Archive Jan 30th 1972 12z                           

              

Even if the first stage fails to produce the easterly "the pump is primed" and we get stage 2 around the end of next week. All the models show the Atlantic being held back with a large HP block established to the north-east. There are variations in terms of the orientation of the HP but most show an air stream from an easterly quarter. The JMA run was produced 12 hours earlier but shows the same time. UKMO and NAVGEM do not go so far out. There is actually quite a good consensus between the others (GFS, ECM, GEM and GEFS) with all showing an easterly flow.  1972 would be better! 

Now let's have a look at the 850s also D9 cross model charts for 0100 on Saturday, February 11th (for those available):

                           GFS 0z                                                       ECM 0z                                                      GEM 0z                                              GEFS ens mean 0z                                  JMA 12z (Feb 1st) T+228  

                      

           Archive Jan 30th 1972 12z                                                                                              Link to Archive Charts

      http://www.meteociel.fr/modeles/archives/archives.php?day=26&month=1&hour=0&year=1972&map=0&region=&mode=2&type=ncep

Well here we do have some disagreement as to the depth of the cold with 850s varying from around -4 to around -10 - again January 1972 would be nice!  If the general set up is broadly accurate, where do we go from there? That will be the period (around D12 to D15 and beyond) where the warmings may have a greater impact and the MJO is going through its favourable phases for assisting much greater HLB. Some models have toyed with the HP building into Greenland and with a broad Arctic air stream moving towards the UK. There was no SSW in 1972 and so the similarities end there. There is plenty to play for. I still believe that February will deliver the goods for coldies with at least some snowfall. I do expect there still to be considerable swings in the models during the rest of this week.

Edited February 2, 2017 by Guest
Correcting typos and to ensure that all the links and charts work properly.