Model output discussion - winter proper underway

[feb1991blizzard]

GFS develops a shortwave at the base of the trough at the tip of S.Greenland which means it could go the way (perhaps to a much lesser extent) of the ICON.

[chionomaniac]

Just had a quick peak at the GFS 12Z - and there is far more amplitude in this run in the Atlantic and Europe, as opposed to the flatter 06Z run.

[Weathizard]

You know it's bad when people are bringing out the ICON  Where's the BOM/CFS when you need them!

The GEFS look dreadful, there's practically unanimous agreement that there's no wintryness on offer, I just hope it's not a washout if it's not going to snow I'd settle for settled conditions with some frosts.

Caveat as usual that nothing is settled, but when an ens suite is that unanimous it's normally an ominous sign, when it's something we don't want! Sod's law.

[Derecho]

GFS 12z keeps high pressure over us, so instead of very mild weather it may be a bit on the chilly side with some fog. Looks like a chart which would bring a temperature inversion.

The UKMO also looks similar.... so that could keep the December CET down.

[Man With Beard]

Just a comment on the GFS continually suggesting snowfall in the next two days. The model (and every other one too it seems) thinks that most of England is currently under snow cover. They are wrong. It seems from a quick question on the SE regional thread that most of the M4 south is snow-cover free. This discrepancy is surely going to lead to errors in the localised modelling in the immediate short-term, as the models will surely be making wrong assumptions about temperatures in localities where snow is not actually laying.

[Fourty Point Three Degrees]

On ‎10‎/‎12‎/‎2017 at 19:31, knocker said:

I'm not sure where the idea of a raging Atlantic originated. I think a zonal pattern is being indicated in the medium term but in the eastern Atlantic the energy is being spread courtesy of the HP block in the east and positive anomalies to the NW and the trough running south to our east. The key may well be if the Azones ridges a little close to the UK

With todays 6z id settle for a stormy Christmas. Its just a question of the what latitude the jet will take as to how stormy it will get.

 

[Daniel*]

I see what chino means, definitely more bloated.  

v

[Derecho]

GFS goes for a classic cold route, strong high lounging around the UK attempting to retrogress to Greenland. This doesn't always work but there are quite a few that started this way (e.g. late December 1880- early Jan 1881).

Something to look out for in future runs. Will go through this route in more detail if it becomes a theme in future runs.

If high pressure can move over the UK we can stay on the chilly side while the polar vortex fires up and then wait for an opening for the high to move north.

[Ali1977]

Mmmmm, at 240 the possibilities of a split PV right accross the pole - this COULD be a very good FI. 

Not too far off I guess!! 

Edited December 12, 2017 by Ali1977

[bluearmy]

A quick look at the polar profile day 10 reveals that this run may not pass any vortex from Asia to Canada as the Pacific ridge is forced further into the pole m

be interesting to see what consequences this has later on 

EDIT: scrap that - it does pass a chunk soon after 

Edited December 12, 2017 by bluearmy

[Catacol]

2 hours ago, Man With Beard said:

Thanks John, and I think this one is worth remembering when looking back at the winter - predicting a good chance of a low pressure dominated winter, especially further north:

Hmmm - your definition of "good chance" is different to mine. That rates lower than average pressure as between 25 and 40% likely. Taken on its own that is an almost pointless percentage, and is made even less relevant when using it as a 3 month average. I have no idea why the Met bother to issue these 3 month broad brush charts - I cant imagine they are much use to anyone. It feels to me as though they don't want to be accused of providing no long range guidance... but then don't actually want to provide any long range guidance in case they get it wrong. I don't think it does them any favours - which is a shame because the 6 - 30 day text forecasts over the last 2 or 3 years have turned out to be very good often.

[phil nw.]

Yes certainly better ridging from the Azores high.If this trend continued we could start to think surface cold under  quiet conditions, especially away from the far north.

No upper cold like we have just had but it would feel more seasonal at least with frosts,maybe freezing fog.

[Summer Sun]

UKMO not quite as quick to clear the last of the cold air away from the east compared to GFS

Once the high arrives it could be a while until it shifts

[Frostbite1980]

You know its a bad GFS run when, when its finished there are no comment lol. All in all pretty uninspiring however i still hold out hope with the MJO entering a more favourable phase as explained by more clever people than myself! I have a feeling the output may look a lot different in the next 5 days.

Edited December 12, 2017 by Frostbite1980

[Glacier Point]

12z GFS op developing a very convoluted upstream flow from day 7 onwards, all courtesy of a temporary extension and retraction of the Asian Jet. Alaskan ridge effectively rips the tropospheric vortex in two. As pure conjecture, 12z would be a heart beat away from developing and easterly flow across Europe. 

[Northern Sky]

10 minutes ago, phil nw. said:

Yes certainly better ridging from the Azores high.If this trend continued we could start to think surface cold under  quiet conditions, especially away from the far north.

No upper cold like we have just had but it would feel more seasonal at least with frosts,maybe freezing fog.

Hi Phil, just trying to learn a bit. As a big fan of freezing fog what synoptics would be best to create a chance for that? High pressure yes, but under what conditions would we get an inversion as the current high pressure shown on the GFS 12z has high 850's? What other factors play a part?

Thanks

[chionomaniac]

5 minutes ago, Glacier Point said:

12z GFS op developing a very convoluted upstream flow from day 7 onwards, all courtesy of a temporary extension and retraction of the Asian Jet. Alaskan ridge effectively rips the tropospheric vortex in two. As pure conjecture, 12z would be a heart beat away from developing and easterly flow across Europe. 

When I got to T+240 I did think that FI would show that. Building blocks.....

[Glacier Point]

Yes Ed. I do believe we have something relatively concrete (Alaskan ridge) to work from here. 

[bluearmy]

This Alaskan ridge is a banker going forward 

how it affects downstream is unknown 

we are now beginning to see more Atlantic amplification around day 10 (the 12z gem looks of interest) 

 

[Summer Sun]

Short ens showing the milder air arriving early next week after a chilly weekend

Still cold at the surface potentially depending on where the high positions its self

Edited December 12, 2017 by Summer Sun

[carinthian]

May be GFS sniffing out a change to the east. This 10 day NH chart shows the removal of the holding pattern over Russia, the first chart to show this for sometime now. I know the later run has the high collapsing but it could easily hold and allow low pressure to the NE to sink into Western Russia .

 C

[Singularity]

  

As trends go, this is a good one from GFS today, and with the tropical forcing helping with amplification plus the dishevelled vortex state, it does seem very credible to see an Alaskan/Aleutian ridge punching well into the Arctic circle with the Canadian vortex lobe shifting W and/then S.. and so on.

Edited December 12, 2017 by Singularity
Misbehaving URL

[I remember Atlantic 252]

Milder 850's SS but a bit of tweaking, could lead to inversion style high, frost/fog, in the south even with warm 850's

[Glacier Point]

1 minute ago, bluearmy said:

This Alaskan ridge is a banker going forward 

how it affects downstream is unknown 

we are now beginning to see more Atlantic amplification around day 10 (the 12z gem looks of interest) 

 

or whether the southern arm of the jet pinches the Alaskan ridge off allowing for a faster retrogression. 

[feb1991blizzard]

24 minutes ago, Glacier Point said:

Yes Ed. I do believe we have something relatively concrete (Alaskan ridge) to work from here. 

Does it matter about the angle though?, the GEFS suite advertises the ridge aimed towards Siberia as opposed to directly through the pole pushing the Greenland lobe further away thus if we did get the Easterly, could the Greenland lobe just be too far East so we are on the periphery of the Scandi high thus not being able to deliver potent cold far enough west to affect us?