Model Output Discussion - cold spell to end Autumn

[bobbydog]

12 minutes ago, Team Jo said:

Aaaaand it’s one run.

moans and one liners have their own thread, please use it if you’re writing off winter off for December/your lifetime/infinity based on tonight’s pub run. At the very least if you’re going to post one frame and with no comment or a Comment with no support other than a tingly feeling in your toes, expect your post to be moved  

aaaand....  thing is jo, its one run which is un-nervingly near to the ECM...

so maybe the toys can be moved to the edge of the pram but throwing should be delayed until at least the morning. but hey, its only the start of winter and its rare anyway to get decent cold spells this early. the fact we're even seeing charts like this at this stage has to be a positive going forwards.

so if we dont get lucky this time-

 

[Nick F]

Really think some are rushing too quickly in presuming that a failure in the northerly next week is a dead cert based on 12z EC and 18z GFS. Yes there’s a good possibility it may transpire this way, but I personally would put low confidence in model guidance after T+144. Here’s why:

- I have noticed and posted recently about the models perhaps not handling with too much confidence the meandering southern and northern branches that extend east over the Atlantic from a split in the jet off eastern N America. Take early next Wednesday the jet profiles are different in orientation and strength over the N Atlantic sector 12z v 18z, this has a knock-on effect of trough and ridge / surface high and low placement and movement. 18z essentially flatter with the northern arm

12z18z

- 12z EC standard deviation charts for ENS and the deterministic run highlight a relatively higher degree of uncertainty to the NW and N of the UK in particular for MSLP and 500mb for mid-next week too

So a few reasons at least why to sit on the fence rather than resign to the idea that the 12z EC and 18z GFS ops are correct and say ‘at least its only early December’

The 12z EPS mean does flatten out the ridge in the Atlantic too in the medium to extended range, but this hides the uncertainty beyond t+144 I think tonight. 

 

Edited November 29, 2017 by Nick F

[nick sussex]

The issue with the ECM was not till post T168hrs.

The PV is not expected to eject to Greenland but remain over ne Canada and this is what NOAA think will happen with it also shuffling a bit more to the nw.

This means energy will shoot east off that and run to the UK, they also expect the Greenland heights to remain which will take the jet on a more southerly track.

The ECM would look like tonights GFS upto T240hrs although we'd expect to see some better ridging to the north. You can't have a positive PNA with a rampant PV stuck over Greenland so that's why a positive PNA often comes with positive heights over Greenland.

This type of set up can produce some good snow. Its of course risky but can produce so lets hope things fall kindly for the UK.

Edited November 29, 2017 by nick sussex

[Frosty.]

To me, there is still a good chance of it turning colder again next week from the north following a milder blip this weekend into early next week..it's not over!

Looking forward to the 00z

Edited November 29, 2017 by Frosty.

[Kentish Snowman in Yorks]

5 minutes ago, mountain shadow said:

It is not set to turn much colder on the ECM and unless there is an incredible turn around overnight in the models then the Ukmet forecast will change accordingly. 

 

Not really an incredible turnaround.  The ECM is one of the only runs I have seen where the Northerly fails to materialise at all - even the 18z GFS gets there in the end.

That ECM run was very much at the mild end of its ensembles as well and so far from being a turnaround I am expecting the ECM to fall in line with nearly all of the other models tomorrow and give us a Northerly or at least the battleground scenario depicted on the latest GFS run.

Just my two penneth anyways.....

[snowbunting]

Been watching the models all day. Fascinating watching them evolve.  I even got weather geeky at my work as ai explained what was happening. 

To me ot sounds as though the ECM is overplaying that Euro high and that it keeps seeking the normalised weather state, ie,  atlantic.

 

The ridging on the Greenie High is crucial. I would say that Scotland is a pretty firm bet for snow next week. 

[phil nw.]

Just flicking through the last few runs and really the key dates for the cold coming south are still the same- around 6-7th December.The difference in the modelling of the Atlantic split flow today has weakened the southward movement though and instead of a clean nationwide northerly we see the battleground idea popping up again.A big difference in the temperatures north and south

As Nick S said a high risk evolution totally reliant on the latitude of the approaching low for some part of the UK to get lucky..If it is a snow fix you are after then this is the type of pattern you need rather than a few wintry showers around coasts and hills and a few frosts from another northerly like we have currently..

 

 

 

[feb1991blizzard]

No where near as many frigid runs on the 18z GEFS as on the 12z, another nail in the coffin.

[Nick F]

Something for coldies to make sleep easier tonight, the 12z EC det. was a warm outlier toward the end for London

 

Edited November 29, 2017 by Nick F

[phil nw.]

1 minute ago, Nick F said:

Something for coldies to make them sleep more easy tonight, the 12z EC dept was a warm outlier toward the end for London

 

Yes note the split around the 6th Dec on the graph the time of the cold air starting to come south again.

[feb1991blizzard]

1 minute ago, Nick F said:

Something for coldies to make them sleep more easy tonight, the 12z EC dept was a warm outlier toward the end for London

 

They don't look a bad suite actually Nick, I thought they would be crap when I saw the FI mean was zonal earlier, if you consider the heat effect of London, loads of members below 5c maxes must intuitively mean that there are a lot for areas further North maxing at a few degrees less, maybe we should take that particular nail back out the coffin!

[frosty ground]

8 minutes ago, feb1991blizzard said:

No where near as many frigid runs on the 18z GEFS as on the 12z, another nail in the coffin.

About 25%

[Duane S.]

Another day of intriguing chart viewing. Despite the doom gloom it is still VERY much game on. Nothing has changed. Just a selection of the 18z GEFS below (and there were other very decent ones as well) for Friday week...

 

[Man With Beard]

Massive split on EC D10 clusters. Cluster 2 looks a bit like one of those GFS pub run classics. Cluster 1 looks even better for cold. I've noticed the ECM op sometimes jumps to one of the main clusters on its next run. There is hope!

[feb1991blizzard]

1 minute ago, frosty ground said:

About 25%

Yes, again looks a lot worse on the mean, but there as you say some potent Northerlies and even a few that return to zonal but are close of give a snowfest before doing so.

[Timmytour]

Hoping for better things tomorrow morning

I don't want to be reminded of how it was last winter

The models start looking frightful
When they have been so very delightful
There's always 10 days to go
Til it snows, til it snows, til it snows
 

[Tim Goffer]

6 minutes ago, Timmytour said:

Hoping for better things tomorrow morning

I don't want to be reminded of how it was last winter

The models start looking frightful
When they have been so very delightful
There's always 10 days to go
Til it snows, til it snows, til it snows
 

Amen! 

 

[Mucka]

Now things have settled down here yet we are still no nearer to resolving the Northerly, may I suggest there is a signal in deep FI for an easterly type flow?

Just as a night cap?

The MetO and some background signals go completely against that and it is only a weakish signal I have been watching the last two days but just as with before this cold spell evolved in the models we shouldn't get to despondent when they don't show what we would like for a while.

I remember before this cold snap the models were showing zonal for a little while and yet we ended up with a pronounced Atlantic block within 10 days or so.

I go away next week and get back around mid month which a couple of days ago seemed perfect timing to miss out on any cold and snow but now the output is more muddled.

Still, I hope the cold comes off and some snow falls and even though any cold does not now seem locked in, that new opportunities crop up around mid month.

It would be great to arrive home just as an easterly is setting up, especially with the Xmas period around the corner.

[Man With Beard]

A couple more from the clusters. At T168, you can see that the biggest cluster is an upgraded version of the op cluster - track the 528 line to the north, and compare the heights over Europe, and you can see it's much more likely to result in a northerly that penetrates further south because of better ridging to the west and lower heights to the south:

Finally the D15 chart - rather messy, the Atlantic ridge has gone (always seems this way in the extended) - possibly stormy, but not the first time a Scandi high has been suggested (control cluster) - potentially very cold indeed if an easterly brews

 

edit: Mucka, great minds think alike

Edited November 29, 2017 by Man With Beard

[Mucka]

31 minutes ago, Timmytour said:

Hoping for better things tomorrow morning

I don't want to be reminded of how it was last winter

The models start looking frightful
When they have been so very delightful
There's always 10 days to go
Til it snows, til it snows, til it snows
 

But they do show signs of stopping

Before the Christmas shopping

For the beast they will all show

Let it blow, let it snow, let it snow

[summer blizzard]

1 hour ago, bobbydog said:

aaaand....  thing is jo, its one run which is un-nervingly near to the ECM...

so maybe the toys can be moved to the edge of the pram but throwing should be delayed until at least the morning. but hey, its only the start of winter and its rare anyway to get decent cold spells this early. the fact we're even seeing charts like this at this stage has to be a positive going forwards.

so if we dont get lucky this time-

 

There are far worse charts that we could be seeing. The vortex is still under attack (and zonal wind forecasts suggest that that is somewhat meaningful) and the low over the eastern US is actually at quite a good angle to avoid a raging Bartlett. 

As i mention elsewhere, there are a few things going against us right now (bad MJO phase, significant Pacific trades forecast) so if we can ride out this period with a lackluster stratosphere then things could be better down the line (though as Tamara has cautioned, there's no guarantee). 

[The Eagle]

Who else is on duty tonight?

Edited November 30, 2017 by The Eagle

[The Eagle]

Ugh, not looking good on either GFS or UKMO at 120 hrs

[CanadaAl]

@The Eagle but look later on at something slyly edging it's way up the east coast of North America. Could be nothing but if that low in the Atlantic merges with that scandi low, it could be game on.  

edit: far too much energy coming off the east coast in this run 

Edited November 30, 2017 by CanadaAl

[Ali1977]

I'm not throwing the towel in, however the Northerly/arctic outbreak next week is now really starting to look unlikely.  The NH still looks full of potential, i.e. no big PV, but as per usual the UK is struggling to benifit. We're not even in winter yet so a loooonng way to go, personally I'd prefer any proper cold outbreaks further into winter anyway when we have colder seas and continents assisting us!!