Model output discussion - winter proper underway

[northwestsnow]

For me UKMO looks better at 144 than GFS anyway- i'm still looking west/north west...

[nick sussex]

4 minutes ago, northwestsnow said:

For me UKMO looks better at 144 than GFS anyway- i'm still looking west/north west...

Yes its better upstream with a better high exiting Canada. Just an issue with that shortwave in the west Atlantic, as long as that doesn't phase with the troughing near the UK at T168hrs allowing a clean exit for the Canadian high towards Greenland.

There are differences though between the UKMO and GFS at T144hrs over the USA.

Annoyingly the MJO forecasts haven't updated for the ECM as that could well pick up the baton and improve on the GFS op run if as forecast its going into phase 7. The GEFS bias corrected have gone crazy today all over the place and the GEFS is taking a few extra days to get into phase 7.

 

[Guest]

A CLOSER LOOK AT THE NORTHERLIES VS EASTERLIES DEBATE

I was going to do one of my comprehensive cross-model analyses for the mid term (around D7 to D10) this afternoon but that’ll have to wait until at least tomorrow (and so will the writing of all my Xmas cards!) as I wanted to examine the subject in my title. I have already mentioned aspects of this in several of my previous posts in recent days. I will still finish with something of a cross-model analysis to demonstrate some of my points raised in this post.

Right, I will make the “bold” assumption that we shall see a broad change of pattern to a colder regime around the turn of the year and into January 2018.  Of course things can change and we might see a “fail”. I am really encouraged by  @Tamara’s update this morning and it would appear that the background signals are now becoming somewhat clearer. The models are still very tentatively exploring the conflicting signals against some of their climatological biases with some considerable swings from run to run. It does currently look like they will increasingly buy into to this pattern change and we may well see a greater consensus and consistency showing up in the runs quite soon (perhaps even as the new week starts). 

There is still much uncertainty over how long this coming week’s mild spell will last. Although some cold shots are possible in advance of any broader pattern change, I will let others focus on the nearer term and the Christmas holiday period. When the models do start to pick up on a general change of the synoptic type they can just very occasionally actually end up with a greater consistency in the eventual outcome but with a huge variation in the interim output while they explore all the routes to the final destination. Some runs might be too progressive in showing greater amplification, while others might be behind the curve. Some great model watching if you can reign in any emotional reactions to the variable output!

Many posters have been speculating on the route to cold and what we end up with. Some say northerlies, some say easterlies but I say both!  Although the background signals favour a build of heights to our north and north-east with HP developing over Scandinavia and perhaps even linking up to the Russian and Siberian HP (later on) this does not rule out an initial northerly which then veers to the north-east and east in due course as the new pattern takes hold.

What I do not accept is the argument that we shall see almost continuous northerlies and no easterlies should a prolonged cold spell come to fruition. Perhaps many of you will be extremely surprised to learn that we have “never” seen an example of a continuous (say 2 weeks or longer) northerly spell since at least 1871 (where the re-analysis charts go back to) and probably a lot further back than that!

The most robust of Arctic outbreaks break down after a while. Even if the jet stream comes nowhere near us for days or even weeks on end (either buckling and meandering around with the UK almost always on the cold side or taking a southerly route through the Mediterranean or even across North Africa) the Arctic air stream will not endure. The longest cold spells typically see a more Polar Continental flow dominating but sometimes with punctured with occasional Arctic outbreaks (mostly recently in December 2010).  

Yes, there have been winters with “only” northerlies (and no easterlies) but these have been broken up by at least brief milder interludes, often with a series of “toplers” followed by Arctic reloads. The most northerly winter was in 1968/69 particularly February. Even that cold spell saw several brief easterlies and one or two short-lived less cold periods. In fact towards the end of that month the Arctic ice sheet (well over 50% bigger back then) was hugging the northern Iceland coast and during the Spring melt several ice bergs were seen as far south as the Shetland Isles! Let’s have a quick look at several of the charts for that period using the excellent NCEP Re-analysis charts from Meteoceil. Here is the link: http://www.meteociel.fr/modeles/archives/archives.php?day=7&month=2&hour=12&year=1969&map=4&region=&mode=2&type=ncep

                     Jan 30th 1969                                   Feb 4th 1969                              0000 Feb 7th 1969  

                            

                1200 Feb 7th 1969                            1200 Feb 7th 1969                         1200 Feb 7th 1969    

                           

I deliberately started with the build up to the strongest northerly of that winter. Those first two charts remind us that the PV can look quite menacing with little sign of a very cold outbreak even just several days beforehand. Then the floodgates opened with a straight northerly. Just an aside - In fact, one of the best examples of a tiny polar low came with this event. It doesn't really show up (no high res chart shown). It moved from the Scottish isles to the south coast from midday to midnight on Feb 7th. I was living in north London and the temp dropped from +2c when the snow started at 6 pm to -5c in a few minutes and we got a 6" dumping from a powder snow blizzard in just 3 hours. Just look at those "to die for" 850s with -16s into northern Scotland!  Remember that 850s and sea surface temperatures are lower towards the end of winter but these exceptional values are just about unachievable these days (on a northerly, not an easterly which has far less sea to modify it en route to the UK). Even the jet stream was only on a (normally rather less cold) north-west to south-east path not a direct north to south route but the ice sheet was much closer (as I said above).  

Persistent northerlies did not last for long even back then and are perhaps even less likely these days with near record low sea ice extent and build-up. We have witnessed consecutive northerlies more or less for each of the last 7 weekends so far this winter but none of them have lasted more than a few days and only one of them was slightly more potent and produced some quite widespread snowfall.

In fact in our epic winter of 1962/63 there were regular brief Arctic outbreaks but the flow was mostly from the nearby continent (as I’ve alluded to in several recent posts). There were actually hardly any long-fetched easterlies either. Once an extensive cold pool had developed over much of central and western Europe, including the UK, the cold air stagnated and deepened in situ with nothing much to move it away or disperse it. We mostly saw a flow from the north-east to south-east quarter drifting off the continent. There were occasional cut off Greenland and Scandinavian HPs helping to top up the cold pool from the north or the east. There were long periods of quite benign but very cold weather with consecutive ice days. There were some memorable snowfalls, mostly from Atlantic systems coming up against the cold block and sliding away south-east (I did a post on sliders recently, as there were at least 10 of them in that winter).

I am NOT for a minute suggesting a repeat of the 1962/63 winter and I was merely showing the type of prolonged colds spells that are possible.  I will focus on several of the patterns shown in the current model output for the remainder of this post. One of the main reasons for easterlies becoming generally more dominant than northerlies in our longer cold spells is that once the Atlantic becomes completely blocked and HLB sets up with the cold regime established, there is nothing to push away any of the cold (surface and uppers) from much of Europe and western Russia. Long lasting Scandinavian HPs can remain pretty stationery for days or even weeks on end. They take up residence over the dense cold surface air. Of course we have to get there first. Let’s have a look at what I mean with examples from the current model output:

              GFS 6z T+288                                        GFS 6z T+384                          GEFS 6z Control T+384                      GEFS 6z Mean T+384   

                                      

The GFS 6z at T+288 already shows a Scandinavian HP (backed up by a few of the GEFS ensemble members). This may be a little too progressive but is quite consistent with the pattern change suggested by the background signals. By T+384 the HP has declined and moved eastwards but just have a look upstream. There is a very +PNA with a strong ridge into the Arctic and an intense Arctic cut off HP extending over the Pole and shattering/splitting the PV. There is weak LP in the Norwegian Sea but the Arctic high is ridging south-south-eastwards towards Scandinavia and is set to link up with the HP further south. I would expect to see a much more powerful Scandinavian HP in early January is this verified. The GEFS control run is less progressive but still has a Scandi HP as well as LP just to our west which appears to be struggling to make eastward progress with a likely battle ground scenario developing. As I always say, one needs to very very careful viewing the GEFS mean chart. Remember it is an average of all 20 perturbations from the ensemble suite plus the control run + the GFS operational run, so it evens out all the charts showing higher or lower pressure. There is HP stretching across the Arctic from the Pacific/Alaskan side through to Siberia and northern Russia where it is stronger. This shows that there must be many ensemble members with strong HP there outnumbering a few weaker ones. The LP is weaker and the PV would be fairly weak too on most of the members. The isobars are not indicative of the surface flow as they weakly show the average pressure (of 24) in each position. Let's move on to some of the members: 

 GEFS 6z Perturbation 5 T+384          GEFS 6z Perturbation 6 T+384        GEFS 6z Perturbation 8 T+384        GEFS 6z Perturbation 13 T+384   

                                            

Yes I have cherry picked a few of the colder charts but this is to demonstrate how the colder regime might set up (if it arrives). Pert. 5 shows a Scandi HP setting up residence plus at strong cut off HP over the pole with the PV starting to be split.  Pert. 6 has an even stronger version of this but with one of GFS's super deep LPs in the Atlantic to our west. I feel that it's unlikely to get much closer to us as the HP starts to dominate the pattern. In fact it appears to be developing a slightly negative tilt and would likely drift south-east into Spain (probably weakening en route) - this would undercut the pattern and if it showed up in the more reliable period, I can guarantee some excitement and a special coverage and analysis from our shortwave and undercutting supremo @nick sussex! Pert. 8 actually shows the colder pattern shaping up very nicely with LP over us. There is a strong band of HP across the Arctic, this time extending from  Siberia, through the Pole and to Greenland, which this time is developing at proper and quite (in recent years) cut off HP. You can see the Arctic HP already ridging down towards Scandinavia and forcing its way between our LP and the weaker LP over north-west Russia. The UK LP will be forced south or south-eastwards and if it puts up any resistance at all, it might well produce decent snowfall. So, on this charter some might think we'll get a northerly (possibly temporarily) but this is actually the route to a powerful easterly (assuming we get any near this type of set up) and exactly what I would be looking for. pert. 13 is again more progressive with a Scandi HP and low heights over southern Europe and an easterly already developing nicely. Furthermore, the upstream pattern looks great too for a sustained bout of cold. There is a strongly +PNA and HP starting to split the PV and seemingly set to link across to the Scandi HP. there is also a belt of strong HP across Russia.

                    

  GEFS 6z Perturbation 15 T+384     GEFS 6z Perturbation 18 T+384       GEFS 6z Perturbation 20 T+384                    ECM 0z T+240                                         

                                      

Pert. 15 is less progressive but may end up with an even better easterly!  Again a strong +PNA with a big HP over Alaska. There is also a powerful ridge of HP extending from western Russia and eastern Scandi through to Greenland which again looks like establishing a proper cut -off HP. Both ridges of HP are just about to link across the Pole, disintegrating the PV. The LP near the UK is almost certain to be forced south or south-eastwards and we'll be in the easterly a few days later on. For a modicum of balance we have pert.18. which is a little behind the curve. Despite a more mobile Atlantic, the LP over us is delivering us a blast of Polar Maritime or even to Arctic Maritime air.  More importantly, there is a powerful Arctic HP starting to split the PV. This set up would produce an initial northerly but as the HP digs further south the pattern should eventually veer to an easterly (perhaps 4 to 6 days later).  Pert. 20 is even less progressive but the UK is under a pretty cold looking cyclonic pattern - perhaps with some significant snowfall to follow (I haven't checked the temp profiles but the pattern looks ripe for some wintry weather). Upstream there is a powerful Arctic HP pushing southwards and this looks set to gives us a longer northerly if it verified and it's too early to say that we would end up with an easterly but I would expect it to deliver a few days later on. 

Now three other models which do not go so far out into the period where the regime change is anticipated. The ECM 0z at D10 has a powerful Arctic cut off HP. This model has only just started to show some more amplified patterns - so it'll be interesting to watch their next few runs. 

 

             GEM 0z T+240                                 NAVGEM 6z T+180     

              

GEM which has gyrated between warmer and colder evolutions  with almost every recent run, also at D10 is less amplified but it too has HP building through the Arctic and looking likely to split the PV a few days later on. Finally, NAVGEM (which seems to come in for some unfair criticism - it's not far behind the big 3 for verification and I like it just as @carinthian does) only goes up to D7/8. This is actually a very progressive run in terms of a later change to a cold pattern. It shows greater early amplification and I can see how a few on here might think it could get interesting for around the Christmas holiday but it would look like the northerly it shows will mostly be to our east, although there may be further interest if the LP over Iceland drops down south-eastwards towards us. My interest is further upstream. Again we see a strong +PNA and a strong HP across the Pole and pushing southwards into the Norwegian Sea. In fact this set up could be the fastest route to cold. The Iceland LP may turn into a slider (not checked how cold the air is in its circulation - I'll leave that for others to analyse) and it would link up with the trough of LP over Scandi. It appears that the whole LP area to our east will be forced southwards by the likely dominant Arctic HP. This would again introduce a northerly but quickly veering to an easterly. It is possible that NAVGEM have got this pattern right but 5+ days too soon! It would be a great coup if they can lead the other models to a much faster evolution of the cold regime.

That's enough from me for now.  Loads of potential and extremely exciting times for coldies and model watching. Can we finally get what we all (coldies that is) seek? The 12z runs coming out now may not be so good and expect continuing swings for a while longer.

Edited December 16, 2017 by Guest
Correct typos and check charts & links

[bluearmy]

21 minutes ago, northwestsnow said:

I honestly dont think this scandy high is happening feb..

The block is going to be of no benefit for the UK its consistently being progged way too far east resulting in us getting an absolute soaking- no thanks!

It could be far enough east to allow a cold trough to settle acros nw Europe whilst a the same time driving WAA north and providing the wave 2 (with the neg EPO ) we may need to split the strat vortex ........

[gottolovethisweather]

2 hours ago, karlos1983 said:

Following slidergate I decided to take a bit of a break, but still kept an eye on the Models and been in and out of here a few times. 

The Models are painting a bit of a mild picture in the more reliable, but mid/long term they don’t have a clue. 

The ensemble show that quite neicely

After around D5 it starts to get a bit messy, we could quite conceivably be seeing 2m temps of 12-14c or 2-5c and longer term even more spread.

Think the modes are in a state of flux, which usually makes for interesting viewing! Bring on the fun and games! Could be a fun few days ahead. 

Good to take a step back from it all, I certainly recommend that as following and commenting on every run and trying to draw conclusions from them will send oneself to a lonely place quicker than the models themselves will do, lol.

I think the spread by D5 is more to do with prospects post the mild blip (Tuesday/Wednesday) for FOG potential rather anything else, but at least a change in type at surface-level. Post-Christmas Day there were hints in the UKMO forecasts for snow in Northern parts, with the words (especially Northern parts), thereby not ruling out other areas. IMBY only one day is forecast to reach double-digits Celcius as things stand but it could be a bit gloomy. The coldest air remaining in the extreme East for another 48 hours yet. Fascinating model ruminating in deep FI right now with the near to mid-term broadly nailed on, the clued-up Strat guys should provide us with some pointers for the final week of December and beyond. 

 

[swfc]

15 minutes ago, northwestsnow said:

For me UKMO looks better at 144 than GFS anyway- i'm still looking west/north west...

good call better ridging existing canada-esb.looks a cleaner smoother run also

[carinthian]

 A very Merry Boxing Day Chart from GFS !  A warm front pushing through on Christmas Day, just what cold lover want for Christmas. Like hell  ! However, I think we will still see many changes again as we head through the week. 10 day charts are a long way off as this winter as already proved so far this winter ( that is they mostly fail to be right ). Even this run shows the possibility of some snow just before Christmas for the Northern part of the UK anyway.

C

 

Edited December 16, 2017 by carinthian

[snowbunting]

The GFS is sending out some very interesting solutions for around Christmas day. Not saying snow but not really saying mild either. Tiny adjustments in models making a huge difference in output. 

 

 Will be really interesting to see how this one evolves with 8 days to go. 

 

 

 

 

[northwestsnow]

ukmo

gfs

[Dennis]

Just now, snowbunting said:

The GFS is sending out some very interesting solutions for around Christmas day. Not saying snow but not really saying mild either. Tiny adjustments in models making a huge difference in output. 

 

 Will be really interesting to see how this one evolves with 8 days to go. 

 

 

 

 

hi im glad you notice too 

[comet]

48 minutes ago, comet said:

ah gfs finally beginning to smell the coffee with the extra amplification into the Arctic from Alaska (pacific side) should be a much better FI we will see.

Low res and it all implodes. earlier signs are more promising though nothing to get excited about in the next week to or more at least.

[bobbydog]

43 minutes ago, feb1991blizzard said:

^^

Yes dyer run that.

quite... 

(i'm not doing it, in case anyone is thinking it...)

still feb, there are 33 more GFS runs before xmas and at just 144hrs, the big 3 dont agree on the way forward. looking at this morning's ECM, we could even see another unexpected evolution. lets see what tonights brings...

[northwestsnow]

Yes i'm hopeful of a better EC this evening

Hopefully it will look more like ukmet than GFS at 144- as far as im concerned anyway..

GEFS look poor again -

But i'm not convinced GFS has the right evolution here.

Edited December 16, 2017 by northwestsnow

[CK1981]

The latest tweet from Ian explains why the Met Office is taking extended zonality with a pinch of salt. Until the background signals have settled, there will be wild swings in model output, so little point in stressing for now. I’m sure we will see many ups and downs between now and Christmas. It does make for interesting viewing though!

[feb1991blizzard]

17 minutes ago, northwestsnow said:

Yes i'm hopeful of a better EC this evening

Hopefully it will look more like ukmet than GFS at 144- as far as im concerned anyway..

GEFS look poor again -

But i'm not convinced GFS has the right evolution here.

GEFS do have some decent runs - in fact quite a few but we're not building on it - its one step forward and one backwards again, theres actually some stonking NH profies amongst them though.

Edited December 16, 2017 by feb1991blizzard

[JBMWeatherForever]

If the met office are taking extended zonality with a pinch of salt, then so should everyone else! There is something different about this winter, and so I would not be surprised at all to see cold taking hold again shortly after Christmas. Next week being just the mild phase, in a transition from one cold period to the next ! 

[IDO]

Hard to see any mid-term potential in the current output. Looks like we have a one wave attack with an EPO ridge from about D5; with the Azores high and Russian high, neither showing much hope of pushing north. The EPO ridge then acts as a conduit to push the polar lows towards Greenland. Inevitably that will lead to leakage downstream and the UK in the firing line for an unsettled period after the Azores/Uk ridge gets sunk. Hard to see this changing much, the GFS has been pretty solid with this of late. There are a few GEFS going elsewhere afterward's, but at D10 the majority offer the same story, hence the mean:

D10 mean:   D15 mean: 

Rare with a setup like this that we will get anything other than the usual zonal muck (after we lose next week's pleasant high).

It's a stubborn setup usually, but this winter I suspect it is simply a passing phase that coldies will have to endure and look for a better profile in the New Year. It's from around D12 when the next Azores wave gets pushed into Europe and tries to ridge north, that the GEFS offer some interest, but transient and minor league winter fayre with that type of pattern.

So assuming GFS suit is on the ball we have a 2-3 week period whilst we move past the next phases.

[tight isobar]

Gefs stamps..out @240 are not without interest.

.....

Still a lot of water to flow under the bridge!!

'To the point'...

There are quite a few varied/and of intrest..through-out....

 

00z run.850s...

Edited December 16, 2017 by tight isobar

[comet]

• Just view the UKMO run and its not without interest, certainly moving in the right direction.

[ACCOUNT DELETED]

Same old story on the GEFS 12z for Porthcawl near Swansea in that the upper air temperatures look set to remain a bit above average throughout, a strong rise in pressure before falling over Christmas but by how much who knows? Lol the ensembles don't as the lines are scribbled everywhere, so I've got no chance of working that out! 

[Ali1977]

An Beast from the.......................far West of the USA!!

[bluearmy]

Incidentally, the ecm op from this morning was from the smallest eps cluster by the time Xmas day arrives and a couple clusters were with a little more nw/se jet axis. 

Edited December 16, 2017 by bluearmy

[northwestsnow]

gfs 192

ecm 192

[N/A]

21 minutes ago, Draig Goch said:

Same old story on the GEFS 12z for Porthcawl near Swansea in that the upper air temperatures look set to remain a bit above average throughout, a strong rise in pressure before falling over Christmas but by how much who knows? Lol the ensembles don't as the lines are scribbled everywhere, so I've got no chance of working that out! 

I completely agree with the ensembles, I think they'll be right and we will end up somewhere between 965mb and 1030mb on New Year's Eve, I'd even put money on it happening  

[snowice]

4 minutes ago, northwestsnow said:

gfs 192

ecm 192

ECM like star wars a new hope