Model Output Discussions 12z 30/11/16

[MattH]

I will firstly add the disclaimer that this is clearly one run of the GFS and I also revert back to my earlier post and what Ian has mentioned too...

However, what does seem quite interesting in the later stages of the GFS is the amount of cold air in evidence to the north of the UK from E Canada right across towards Scandinavia. There is often more variation in the location of the coldest air mass rather than a more uniform area of sub -10C 850mb temperatures.

This can be a double-edge sword in the fact that the cold air, actually very cold air, is not too far away to the north and if the right synoptics allowed it then it would obivously flood southwards. However, and as usual from our point of view, having that volumn of cold air present will do nothing more than combine with the usual tropical 'warmth' over the western N Atlantic to increase baroclinicity and hence allow areas of low pressure to develop along a general W'ly flow over the N Atlantic, the latter being the most likely evolution for now.

Interesting nonetheless for the 06Z GFS to have the bulk of the N Hem cold over this side of the pole, note the lack of cold over Alaska for example and into that side of the polar region.

Matt.

[phil nw.]

Ah well time to take a breath as the excitement of recent model runs has now died down.

It's a shame to lose the crisp frosty weather that many of us have had recently but the high will soon be on it's way se and a look at Tuesday's fax shows the milder south westerly flow heading into the UK on it's western flank.

We can see from the NH view that the vortex gets stretched east west in the mid-term which isn't great for getting cold here.It situates low heights over Greenland which as we know is our default +ve NAO pattern along with a high over Europe and/or the Azores..

Day 10 ECM/GFS Mean

So we go into the westerly pattern next week but it doesn't look one of the most active Winter ones we have ever seen with rainfall spikes on the graph, certainly further south still quite modest, although some north western areas may see more nearer the lows as they move across.As for the temperatures they look mild for about a week then tail off towards average around mid-month.The graph is for C.England

which maybe is a sign of a rather colder west/north west flow in week 2 as the jet eases further south.

As other have said though not easy to see a way forward beyond the next week or so with no strong height anomalies currently modeled -maybe just a sign at the end of the gefs run of some building of +ve height anomalies towards the north east but as ever we need to see some consistency in that in future ens runs.

 

 

[bobbydog]

7 minutes ago, MattHugo said:

I will firstly add the disclaimer that this is clearly one run of the GFS and I also revert back to my earlier post and what Ian has mentioned too...

However, what does seem quite interesting in the later stages of the GFS is the amount of cold air in evidence to the north of the UK from E Canada right across towards Scandinavia. There is often more variation in the location of the coldest air mass rather than a more uniform area of sub -10C 850mb temperatures.

This can be a double-edge sword in the fact that the cold air, actually very cold air, is not too far away to the north and if the right synoptics allowed it then it would obivously flood southwards. However, and as usual from our point of view, having that volumn of cold air present will do nothing more than combine with the usual tropical 'warmth' over the western N Atlantic to increase baroclinicity and hence allow areas of low pressure to develop along a general W'ly flow over the N Atlantic, the latter being the most likely evolution for now.

Interesting nonetheless for the 06Z GFS to have the bulk of the N Hem cold over this side of the pole, note the lack of cold over Alaska for example and into that side of the polar region.

Matt.

Yes Matt. Cold air is never far away during the past few runs. Just as an example-

That chart would bring snow (fairly brief but still significant) to almost everyone.

I wouldn't call it a trend yet but a recurring theme seems to point towards a more southerly tracking jet, bringing with it that (much) colder air.

[Ali1977]

Some ENS close to splitting the vortex at 180, could be plenty with interest around day 10 and onwards 

[gottolovethisweather]

19 hours ago, Ravelin said:

GFS 12z at t114 has everything a shifted fair bit more 'top right' compared to the 6z, which makes a huge difference to the centre of the low over the US

6z   12z

 

 

 

 

Indeed our eyes need to be drawn to developments of the Eastern Seaboard post D5 onwards, as alluded to in my post from this morning.

 

 

Edited December 3, 2016 by gottolovethisweather
Please delete. Duplicate post

[gottolovethisweather]

2 hours ago, Nick F said:

Sound advice from Matt to just sit back and see if any solid trends develop in the medium to long range which has been volatile of late, with the  anomalies on the 11-15 day EPS and EC46  shifting with each run or generally just a weak/tenuous rather than a strong signal.

In the short-to-medium range, fair few GEFS members supporting the 00z EC det idea of trough disruption over mid or east Atlantic, probably because of the deep cold vortex dropping SE over N America later next week causing some amplification downstream, throwing a ridge N towards Iceland/NE Atlantic, followed by a more southerly tracking jet across the Atlantic as the jet flattens out behind the wave. Maybe a trend to watch out for over coming runs ...

 

 

2

 

 

Hi Nick, I'm not sure if we're speaking about the same thing here but I mentioned it in passing a couple of times yesterday on here, the timescales involved seem to match up.

There are hints now also off the Eastern seaboard of Atlantic heights returning by then. The latest 0z UKMO operational run seems reluctant to drop any heights down IMBY either. Thi could indeed become a very short period of Atlantic influence (largely biased towards affecting NW Britain anyhow) as things stand, given the uncertainty from 10th December onwards.  

 

It has made for some fantastic reading in here this morning, so much better than those one-liners. 

Edited December 3, 2016 by gottolovethisweather

[bluearmy]

Spread evident but around a seasonal base 

[fergieweather]

1 hour ago, Frosty. said:

The mean charts have been / are uninspiring too for coldies, not just the operationals with just occasional glimmers of hope from individual perturbations.

Yes, but there's the key points encapsulated together in your post: the mean fields will always mask the members that are less energetic/stray from climatology. Inspection of individual stamps/clusters is critical to appreciating the actual breadth of potential outcomes... and in this case, the reasons for such marked uncertainty being expressed!

[IDO]

28 minutes ago, bluearmy said:

Karl - I suspect ian means the ens when he refers to op models as they are suites that contain an operational run 

tbh - the mean anomolys end week 2 are saying blocked rather than zonal so not sure they are really headed away from monthly tools. 

The problem with the mean and clusters at the moment is that without really looking at them it is hard for most of us to judge the EPS output. The clusters may have a group showing NE blocking at D14, but at D16 are they the same members continuing the blocked theme, or is it a case where with have a transient wedge of heights crossing with differing time scales, so the impression over a 5 day period is of heights in the NE? So not really blocked, just a sampling at a specific time (even if they are 3-5 day means this could also apply).

With the GEFS we can see each member and some this morning are saying 50% GEFS blocked, but if you look at each member that will show HP at say D13, and look two days before and 2 days after, it is not in fact a block, just the flow of the NH pattern and that snapshot at D13 is just that.

Until I see a consistent driver for a pattern change I will go with the status quo; no definitive blocking pattern, just transient themes as the PV makes its mind up to where it will go after it drains from east to west after D7/8; a theme the GFS has been clear on for many runs.

6 minutes ago, Ali1977 said:

Some ENS close to splitting the vortex at 180, could be plenty with interest around day 10 and onwards 

That has been forecast for days, a weak area of LP across the pole. However it is consistently wiped out by the draining of the Siberian vortex to the Greenland region shortly afterwards and I see little hope of that not happening based on the GEFS. Also this is apparent on the ECM D10 mean:

D10 ECM mean: D10 anomalies op:  D10 anomalies mean: 

The ECM D10 op off on one again it would seem.

 

[karyo]

A bit of interest from the ECM this morning in the far reaches of FI. Apart from that, a familiar picture of the last few Decembers with high pressure to the south/southeast of us and low pressure in the Atlantic and Greenland keeping us mild with brief cooler spells.

There were some posters a month or so ago that pointed out that the signals for northern blocking were false due to the record low Arctic ice and that as the ice coverage naturally increases over the coming months the northern blocking will also disappear/diminish and we will be back to our usual winter pattern. I wonder if the Arctic ice has reached this stage now.

Looking at the current ice extend we can see that it is still lowest on record but increasing fast and it is about to reach 10M km2. With the stratospheric vortex expected to return to the Arctic the ice recovery may speed up more in the coming weeks. But even that may not be necessary as the warm SSTs anomalies in the north Atlantic can fire up the jet as the interact with the increasing ice cover further north.

https://ads.nipr.ac.jp/vishop/#/extent

[blizzard81]

Quite big support for a meaningful drop in temps from the gfs 06 ensembles last three days of the run which is around 18th/19th Dec

[Ali1977]

Some very very good ENS this morning, 6 or 7 very cold and possibly the best so far this season - are we back in the game coldies.

[Summer Sun]

Big drop in the 850's beyond mid-month

A cold start to Christmas week certainly can't be ruled out

Edited December 3, 2016 by Summer Sun

[Banbury]

Some very interesting ENS from the 6z that's for sure

[Frosty.]

19 minutes ago, fergieweather said:

Yes, but there's the key points encapsulated together in your post: the mean fields will always mask the members that are less energetic/stray from climatology. Inspection of individual stamps/clusters is critical to appreciating the actual breadth of potential outcomes... and in this case, the reasons for such marked uncertainty being expressed!

Thanks for explanation, I appreciate it

Edited December 3, 2016 by Frosty.

[karlos1983]

Looking better. Let's hope that continues over the weekend 

[bluearmy]

The 06z gefs more than interesting though I recall it was the 06z suite which was over amplified a few days ago

IDO - your point about ens without clusters is well made although viewing run to run comparisons on the mean/anomoly in conjunction with the prob percentages can help somewhat. Of course the end result could easily be a mean between the favoured clusters which isn't shown anywhere !!

[ITSY]

Well well well. Are we back in the game? Several greenies and nly blocks setting up. Worth noting that many of those which don't deliver cold still wind up establish reasonably high lat blocks in our vicinity late on. Certainly encouraging - this for the East Midlands. Eyes for the 12z's!

edit: let's not get too carried away. It was indeed Tuesday's 06z run that delivered v amplified solutions, followed as we know by three days of fairly relentless backtracks. I think we take this run to suggest that no one really knows quite was is going on and that there is plenty of time for this to yet turn out either way. Encouraging but cautiously so...

Edited December 3, 2016 by ITSY

[bobbydog]

Just now, Ali1977 said:

Some very very good ENS this morning, 6 or 7 very cold and possibly the best so far this season - are we back in the game coldies.

Yes Ali, just been looking (up to 348hrs). Some very good perturbations, 5 of which give us classic greeny highs, including this little gem-

Now where have I seen that before?...

 

[Ali1977]

Those ENS are good but don't tell the full story, for instance the Control isn't too cold - but look at this, absolute corker beyond this towards Xmas!!

[ITSY]

1 minute ago, Ali1977 said:

Those ENS are good but don't tell the full story, for instance the Control isn't too cold - but look at this, absolute corker beyond this towards Xmas!!

Equally, a lot remain fairly mobile so let's not count chickens yet. The last few days may well yet prove that we do that to our own peril, and at severe costs to our mental health...

[IDO]

1 minute ago, bluearmy said:

The 06z gefs more than interesting though I recall it was the 06z suite which was over amplified a few days ago

IDO - your point about ens without clusters is well made although viewing run to run comparisons on the mean/anomoly in conjunction with the prob percentages can help somewhat. Of course the end result could easily be a mean between the favoured clusters which isn't shown anywhere !!

I thought you would look deeper, just I am a bit wary without viewing myself. Thanks.

The 06z is a law to itself and I would never take it seriously (after D7), especially at a weekend.

[mountain shadow]

I wonder if the models are now getting to grips with the Indian Ocean complications which was masking the movement of the MJO?

Hopefully GP or Tamara can advise whether we can now see the woods from the trees.

[Robbie Garrett]

9 minutes ago, Summer Sun said:

Big drop in the 850's beyond mid-month

A cold start to Christmas week certainly can't be ruled out

When was the last time snow fell on Christmas Day in London?

[Summer Sun]

1 minute ago, Robbie Garrett said:

When was the last time snow fell on Christmas Day in London?

2001 I believe