Model Output Discussions 12z 01/09/2016

[Mucka]

I think that if ECM goes a similar route tonight the forum, for once, is probably being a little over cautious re our first cold snap/spell.

The trigger low and upstream amplification are still to be nailed down but it will be difficult to escape pulling cold air from the N/NE once that low clears into the content around day 7.

The fine detail will depend on the behaviour of the trigger low but whether we get a chilly snap or cold spell will depend on upstream developments around SW Greenland. 

Get enough amplification there and close off the Atlantic and the cold will flood West and we will have our first cold spell locked in.

If things are a bit flatter and we get shortwaves pushing through and down the Eastern flank of the Atlantic ridge then it will likely just be a little chilly with rain from time to time.

I am normally cautious and many a potential cold spell has been scuppered by pesky shortwaves popping up and misbehaving around SW Greenland but barring a sudden reversal in the output tomorrow I just can't see how we avoid at least some chilly weather but more likely a cold spell (relatively for time of year at least) as although the actual cold, should it arrive, won't show until early FI, the synoptic that would produce it is delivered in fairly reliable time-frames.

I feel quite bullish about our first cold spell beginning in around a weeks time. Hope that doesn't come back to haunt me in a couple of days. 

[Summer Sun]

Possibly some snow for parts of the Pennines by D10 and the mountains in Scotland as one would expect at this time of year

[Frosty.]

This is sensational stuff from the Gfs 12z..November snow event in the north and another reload!

Edited October 29, 2016 by Frosty.

[knocker]

The GFS this evening not hugely different in the reasonable time frame. It phases the second trough with the easterly LP and tracks it south east over the UK at the end of the week. The resulting surface analysis has a depression 989mb over Denmark 12z Saturday resulting in cold unstable airstream over the UK.

The major upper trough that forms out of these machinations forms a positive tilt south of the UK which allows the next upper low from the Canadian feeder to wing in on the10th but that is getting ahead of ourselves. I'd better post now and see if I can fit it in during the flurry

Edited October 29, 2016 by knocker

[Zakos]

No point speculating about the end of the cold spell - it is over a week before it is even due to start. In terms of the onset of the cold spell (second week of November) the upgrades continue, with the cold looking more brutal and further west on each run, and 

18z00z

06z12z

An insane chart -  the Atlantic is completely blocked off from Europe, and over half of North America is experiencing Atlantic weather; air sourced from the Atlantic is spreading eastwards right across to Alaska. 

Edited October 29, 2016 by Zakos

[Frosty.]

2 minutes ago, Zakos said:

No point speculating about the end of the cold spell - it is over a week before it is even due to start. In terms of the onset of the cold spell (second week of November) the upgrades continue, with the cold looking more brutal and further west on each run, and 

18z00z

06z12z

An insane chart -  the Atlantic is completely blocked off from Europe, and over half of North America is experiencing Atlantic weather; air sourced from the Atlantic is spreading eastwards right across to Alaska. 

You get the feeling we would have to be extremely unlucky to miss out on an early / mid November arctic blast, the models are continuing to firm up on it though which is fantastic!

[Zakos]

1 minute ago, Frosty. said:

You get the feeling we would have to be extremely unlucky to miss out on an early / mid November arctic blast, the models are continuing to firm up on it though which is fantastic!

Yes I agree, Its pretty much a given that November is going to get progressively colder until at least the 3rd week in my opinion.

As Mucka said, I suspect people are being overly cautious, especially if the ECM backs up the GFS today.

Throughout the entire run we have northern blocking completely dominating the UK weather.

201320142015

The last three years at this time of year saw Atlantic dominance.

In 2015 at this time, there was a similar attempt to build heights over Greenland. However notice also the huge negative  height anomaly in the Atlantic, caused by the jet stream firing up due to the very strong El Nino. 

fast forward a week or so in 2015, and the negative height anomaly further increases, and we are left stuck in a Bartlett pattern

This year, we arent seeing any sign whatsoever of the Atlantic firing up, and with the AO negative and predicted to dive further... there is every reason to be optimistic IMO, and as you said we would have to be extremely unlucky to miss out!

[Frosty.]

The Gem 12z has improved since the 00z, let's hope it keeps playing catch up with the Gfs!

[Ali1977]

Whilst the Op was great, the GEFS don't seem quite as keen on the extreme blocking to the North and west later on in the run...We did get warned about getting carried away beyond the 4th Nov. The Op could be correct , but without back up from the GEFS we need to be cautious !!

Edited October 29, 2016 by Ali1977

[Frosty.]

The GEFS 12z mean looks impressive next weekend with plenty of perturbation support for an Arctic Nly / NEly airflow.

[Mucka]

GFS ensembles still showing fairly wide scatter 

 

 

[Daniel*]

Spotless sun the significance is unknown to me but the marked limited solar activity could be resulting in the lack of versatility (I'm not sure but I recall reading on here, periods of increased solar activity can flare up the Jet Stream).

This Autumn the Atlantic seems to be heavily sedated, it's rather unusual in fact it's quite comparable to 09/10 - enabling recent anticyclonic weather to lock in this Autumn, and perhaps gives a bigger incentive for a cold northern blocking scenario to lock in or sustain? Which we're seeing in the models to different extents. 

Edited October 29, 2016 by Changing Skies.

[Man With Beard]

27 minutes ago, Mucka said:

GFS ensembles still showing fairly wide scatter 

 

 

Yes, very few runs with a sustained block into Greenland / Iceland, and holes in the PV becoming fewer by mid-month. Op run far probably the best for for sustained cold. Other than that, most runs seeing a generally northerly flow but not of arctic/siberian origin so not particularly wintry at this time of year.

Still, probably too much to ask to get ensemble members on board with a cold spell until nearer the time - I seem to recall many a cold spell where the ensembles kept bringing in mild weather by T168, only to be overturned dramatically within 48 hours.

The key is to get to that NEly is the first place - once we get into that pattern, it may transpire that it is harder to ditch than the ensembles pretend.

[Met4Cast]

Whilst there is a fair amount of scatter in the 12z ensemble suite, it's fairly obvious we're going to be around or below average for quite some time when this initial warm spell ends in a few days time. Not surprising to see the Control run being one of the warmer runs considering the lack of any blocking on it.

[Mucka]

8 minutes ago, Man With Beard said:

Yes, very few runs with a sustained block into Greenland / Iceland, and holes in the PV becoming fewer by mid-month. Op run far probably the best for for sustained cold. Other than that, most runs seeing a generally northerly flow but not of arctic/siberian origin so not particularly wintry at this time of year.

Still, probably too much to ask to get ensemble members on board with a cold spell until nearer the time - I seem to recall many a cold spell where the ensembles kept bringing in mild weather by T168, only to be overturned dramatically within 48 hours.

The key is to get to that NEly is the first place - once we get into that pattern, it may transpire that it is harder to ditch than the ensembles pretend.

Yes in reality it can still go TU but my confidence is that the trigger low is within the reliable (more or less) and upstream has more amplification as a result.

Once (if) the Atlantic lows are cut off at 144 by the Atlantic ridge then some form of cold snap/spell is assured.

Whether we can get it cold enough for snow to fall to low levels at this time of year is another question.

Edited October 29, 2016 by Mucka

[knocker]

1 hour ago, Zakos said:

No point speculating about the end of the cold spell - it is over a week before it is even due to start. In terms of the onset of the cold spell (second week of November) the upgrades continue, with the cold looking more brutal and further west on each run, and 

18z00z

06z12z

An insane chart -  the Atlantic i

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is completely blocked off from Europe, and over half of North America is experiencing Atlantic weather; air sourced from the Atlantic is spreading eastwards right across to Alaska. 

I must admit I'm quite puzzled by this comment. There is a fair bit of WAA going on but sourced in the Atlantic it aint. Much more to do with the Aleutian low and ridging in the eastern half of North America.

Edited October 29, 2016 by knocker

[Summer Sun]

The GFS Op was on the cold side when looking at the ens the mean hovers around 0 from the 6th

[Ali1977]

ECM supporting the GFS pretty well but no sure it'll have the same outcome ref the cold uppers as the low in scandy isn't in the best position and could do with heading south a few hundred miles.

Edited October 29, 2016 by Ali1977

[Matthew.]

The ECM 12z showing LP homing in after midweek on a WNW-ESE trajectory. A real chill in the air as November approaches with a break in the settled weather of late. Chilly and showery from Thursday:

[Met4Cast]

No real WAA into Greenland on the ECM but we still manage to build in a decent Greenland High. Seems like even when things go a bit wrong, they come out on the otherside being right.  ECM not quite as good as the GFS, but still a decent shot at cold 

[Zakos]

24 minutes ago, knocker said:

I must admit I'm quite puzzled by this comment. There is a fair bit of WAA going on but sourced in the Atlantic it aint. Much more to do with the Aleutian low and ridging in the eastern half of North America.

Correct but I wasn't referring to WAA, i was referring to the very strange pattern over North America, with an easterly flow across the entire continent.

North America is under the influence of atlantic air with the flow spreading all the way the the Pacific.  I should have chosen a better chart to illustrate this to be fair.

 

Edited October 29, 2016 by Zakos

[Ali1977]

4 minutes ago, Daniel Smith said:

No real WAA into Greenland on the ECM but we still manage to build in a decent Greenland High. Seems like even when things go a bit wrong, they come out on the otherside being right.  ECM not quite as good as the GFS, but still a decent shot at cold 

Much better now though 

A little influence of WAA and the scandy low dropping south slightly and it's still worked out well...

Edited October 29, 2016 by Ali1977

[weirpig]

Regardless of uppers etc the theme is on all models the blocking in the Atlantic . It's November and no Atlantic  pinch yourself this year is very unique 

[knocker]

13 minutes ago, Zakos said:

Yes but I wasn't referring to  WAA, i was referring to the  very strange pattern over North America, with am easterly flow across the entire continent.

North America is under the influence of atlantic air with the flow spreading all the way the the Pacific.

 

I'm sorry but I completely disagree. I think you are misreading that chart at T336. Mind those charts are not very clear. Here is the 500mb contour chart for T336 which I think is the chart you chose with the wind barbs and they coming from the westerly quadrant. I will post the 500mb contour chart with anomaly (just ignore the latter) and again the upper flow will be along the contour lines. As a matter of interst you say you aren't talking about the anomaly (which I agree you shouldn't be) and then post an anomaly chart.

Edited October 29, 2016 by knocker

[Mucka]

Similar theme from JMA.

If we can get some consistency through tomorrow then perhaps we can start to add things to our cold wish list, such as the pattern being backed West a little, a bit more amplification in the Atlantic sector, colder uppers etc.

Edited October 29, 2016 by Mucka