Model output discussion - winter proper underway

[karlos1983]

yesterday's 12z ensembles weren't without interest!!!

New one's will be out within the hour, can we get some momentum towards cold around or just after Christmas Day 

[karyo]

7 minutes ago, bobbydog said:

the trend continues...

Pure fantasy! At this stage the gfs shows that bombing low in the Atlantic move northwestwards! lol

[TEITS]

So just like yesterday the 06Z teases us with a much more promising outlook. Shame the GFS doesn't go out to +400 because my word we would be drooling!

Still back to reality and unless this new amplified trend is shown on subsequent runs then I shall put it down to an outlier due to it being the 06Z run.

[Man With Beard]

GFS 06Z - if it is going to turn colder for Christmas, then this is by far the most likely way it will happen. 

  

Those of us who have been watching these models for 15-20 years know very well that models can often miss a background signal that leads them to go through a whole period systematically forecasting one recurring pattern in FI, but which then gets modified to a different recurring pattern by the D4-D7 period.

Last summer being a case in point - in July, most models (including the great Glossea) kept forecasting settled weather, and yet come D5 a sneaky trough would keep getting into the pattern - over and over again, and the settled period never came for many. Likewise, last winter was particularly painful for coldies as the ECM monthly kept sticking a positive height anomaly to our north - again, came to virtually nothing until the winter was almost over.

But - in contrast - the pattern we have had this winter so far is indeed the positive height anomaly to the NW. Of course, patterns do end eventually. But when a pattern has been repeating time and time again (as it has done in the past 5 weeks with NW heights), I always leave a little room in my mind for the pattern to re-emerge even when everything says pattern change.

My rule on a pattern change is - do not absolutely bank on it until it is showing inside D5.  The models don't know everything, we don't know everything, the Met Office don't know everything - and they may have missed a background signal which caused the weather we've recently had and which may still be present. 

Now to be clear: There's absolutely zero support for this within the ECM ensembles (in fact more support for a rise in heights to the east):

but all the same, I'm still putting more eggs in the NW heights basket, rather than the NE one.

 

If I had to rate the chances for, say 23rd December, my personal opinion atm would be something like this:

40% = ECM 00Z option - westerly flow - unsettled north - average temps or above

30% = GFS 06Z option - north-westerly flow - a repeat of the cold plunges of the past few weeks.

20% = GEM 00Z option - high pressure over the UK - dry but frosty in the south

10% = A surprise Scandi High

 

Edited December 13, 2017 by Man With Beard

[Nick F]

8 minutes ago, Dafydd Tomos said:

GFS 6z continues this theme too, could be more snow over S & SW England as well as the far South of Wales than Sunday if this verifies. 

Just a quick word re: the snowy looking GFS projections for tonight / Thursday morning ...

IMO GFS always progs dew points too low in a NWly regime, so any snow likely only settling over the hills in the north and west. There could be some wet snow mixed in with the heavier bursts / showers at low levels, even in the south and east, but unlikely to settle unless with height.

Could be treacherous over the higher routes of Wales and N England in the morning though.

[Purga]

5 minutes ago, TEITS said:

So just like yesterday the 06Z teases us with a much more promising outlook. Shame the GFS doesn't go out to +400 because my word we would be drooling!

Still back to reality and unless this new amplified trend is shown on subsequent runs then I shall put it down to an outlier due to it being the 06Z run.

You mean you haven't had a quick rummage around to check where you'd put that sledge wax TEITS?

[offerman]

28 minutes ago, Nick F said:

Well, the Azores high is a semi-permanent ridge, part of a belt of sub-tropical high pressure systems around the northern hemisphere, Californian high and Bermuda High to name but a few. So probably why it doesn't move much and often we see it extend into Europe when the trop PV is strong to our NW.

Brilliant. Thank you nick . 

[bluearmy]

I have no confidence in that gfs solution and yet I’m reminded that I have thought (and posted) that a change from the more  ‘zonal’ outlook with the ridging closer tot the uk will be picked up first by the ops rather than the ens 

I guess for the time being, the comment that yesterdays dull 18z run was nothing more than a rehash of a 12z gefs member is just as true of  the 06z being a re hash of a 00z gefs one. I’m sure there was a similar run in there !! 

 

 

 

 

Edited December 13, 2017 by bluearmy

[Daniel*]

Right on cue. Now that’s a big freeze! 

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[Methuselah]

A wee bit nippy!

[jvenge]

The Op was the pick of the run, but you can see some of the other ensembles (far from a majority solution) smell something similar in the extended range, even if they do end up at different places.

Bigger takeaway being that many of them favour a move away from mild, even if they get there in slightly different ways and don't give anything particular cold along the way.

Edited December 13, 2017 by jvenge

[bluearmy]

ThInking back to winters past 2009/10 and 2012/13 where we saw a mundane model outlook suddenly change, I recall the ops showed a fair bit of continuity once they stumbled across the new route of travel and a ridge thrown to our ne was often the precursor. 

However, the models (op and ens) are now running at much higher resolutions. 

There is nothing to do here but wait and watch !!

[Kentish Snowman in Yorks]

Anybody calling mild for the rest of the month is very brave in my opinion.

We are certainly now looking at a milder spell of weather (at least 850s wise) starting Monday until around Friday next week but anything after that is up for grabs in my opinion.

The GEFS this morning show a huge scatter from the weekend before Christmas onwards and the 6z GFS op run also shows what is possible at short notice with the current setup.

Game On!  

Edited December 13, 2017 by Kentish Snowman

[Daniel*]

1 hour ago, Ali1977 said:

If verified that Scandy high would be prolonged and very cold, let's hope some ENS support is on its way.

There’s not much the operationals will tend to lead the way ECM god forbid, 2 will do.

 

[Glacier Point]

06Z GEFS and op has just added to the model fog cerca 22nd onwards. As per previous thoughts, we're approaching a transitional phase, timed around the switch from December to January.

The low frequency tropical forcing signal has, and will continue to be centred around 140E - 160E in the Western Pacific. 

That's likely to maintain angular momentum in an elevated state relative to La Nina, so persistent signal for the GWO in phase 8 during the Christmas and into New Year period. The composites for this phase over the two separate months highlight the issues ahead of the modelling:

That's solid support for the building Alaskan ridge in the medium term modelling and, persistence of ridge to our west.

Therein the changing seasonal wavelengths bring about the change. Trough signal back over Europe and height rises to our NE and N.

The Alaskan ridge poses some questions: where does it go given the composites for January don't see it sticking around too long; does it migrate poleward and become absorbed into the Arctic circulation (as looks likely)? How then does the North American trough behave ? Composite for January looks good for the ridge developing in the extended modelling off the SE USA, so some westward movement of the trough over Canada looks reasonable. Longer term, a reboot of tropical convection across the Western Pacific and increasing angular momentum look to favour a phase 4 transition of the GWO into January:

Lots to be interested in and a non-numerical approach offering plenty of clues ahead.

[Summer Sun]

Lots of scatter developing from the back end of next week

Edited December 13, 2017 by Summer Sun

[Methuselah]

15 minutes ago, Kentish Snowman said:

Anybody calling mild for the rest of the month is very brave in my opinion.

Game On!  

Absolutely agree, KS: to call anything would, IMO, be fruitless... At the same time, the high degree of model-uncertainty is (both of itself and in conjunction with the long-term signals to which GP and Tamara allude) a good enough reason for optimism...I think!

[West is Best]

The way the ensembles have shown such huge scatter for a few days has given rise to some optimism of a return to cold conditions. It was probably inevitable that at least one of the operationals would pursue a cold perturbation. It will be very interesting to see the 6z ens. I'm expecting the scatter to be huge again, with plenty of mild members. It's the trending for which we're watching. If increasing numbers of cold members appear and the spread tightens, then I'm going to sit up. 

Here's hoping

Edited December 13, 2017 by West is Best

[tight isobar]

14 minutes ago, West is Best said:

The way the ensembles have shown such huge scatter for a few days has given rise to some optimism of a return to cold conditions. It was probably inevitable that at least one of the operationals would pursue a cold perturbation. It will be very interesting to see the 6z ens. I'm expecting the scatter to be huge again, with plenty of mild members. It's the trending for which we're watching. If increasing numbers of cold members appear and the spread tightens, then I'm going to sit up. 

Here's hoping

Trying upload' london 6z ens..

But cannot for some reason!!

Well worth a look!

Edited December 13, 2017 by tight isobar

[Daniel*]

It does seem to happen a lot 06z is more amplified than 00z I can't stick my finger why, this is probably coincidental nothing changes merely the time the run comes out. 

[ukpaul]

1 hour ago, Nick F said:

Just a quick word re: the snowy looking GFS projections for tonight / Thursday morning ...

IMO GFS always progs dew points too low in a NWly regime, so any snow likely only settling over the hills in the north and west. There could be some wet snow mixed in with the heavier bursts / showers at low levels, even in the south and east, but unlikely to settle unless with height.

Could be treacherous over the higher routes of Wales and N England in the morning though.

Euro4 also has favourable dew points, although not as negative as the GFS. I'll be up at 160m asl this evening for a Christmas meal and the local forecast suggests snow until gone midnight, so I'm keeping a close eye on it.

[West is Best]

Well the operational is definitely on the cold side. But there continues to be massive scatter with a decent number of cold members.

Cause for optimism here, as an adjunct to the upstream signals. It means that the GFS can see a number of viable possibilities with certain pertubations. Interesting.

[ACCOUNT DELETED]

8 minutes ago, ukpaul said:

Euro4 also has favourable dew points, although not as negative as the GFS. I'll be up at 160m asl this evening for a Christmas meal and the local forecast suggests snow until gone midnight, so I'm keeping a close eye on it.

I'm keeping a close eye on that too (although it seems a relatively low risk) as I'm due to drive up to Merthyr Tydfil tonight with my mate to do a Christmas gig. Hope we won't get stuck there! 

[Pembroke Dangler]

3 minutes ago, West is Best said:

Well the operational is definitely on the cold side. But there continues to be massive scatter with a decent number of cold members.

Cause for optimism here, as an adjunct to the upstream signals. It means that the GFS can see a number of viable possibilities with certain pertubations. Interesting.

What interests me is that the cold members go quite a way below the mean so it would appear that if it does go the cold route it could be a potent one and just in time for Xmas day it would appear. 

[Daniel*]

2 minutes ago, Pembroke Dangler said:

What interests me is that the cold members go quite a way below the mean so it would appear that if it does go the cold route it could be a potent one and just in time for Xmas day it would appear. 

Nothing overly potent being signalled for now, I only see one member which matches with the OP synoptically. A flutter on a white Christmas for somewhere in the north might be worth it.