Model Output Discussions 12z 01/09/2016

[blizzard81]

1 hour ago, Faronstream said:

It is weird to see that ECMWF has a high pressure that grows in from the SO Atlantic in the 00z run, i belive more in GFS with Atlantic domination

But this is what the GFS was showing on most of it's operational runs for the same time frame. ECM now jumps on board only for GFS to jump ship - a familiar tale. I expect GFS to climb back on board soon. A fine, warm first half to October beckons.

[phil nw.]

Just looking at the combined London ens.graphs and in week 2 we can see differences between the 2x00z model runs.

If we view the rainfall and wind strength in particular the red ECM lines show a comparatively dry and calm second week against the wetter and windier GFS ens(blue line).The temperature graph gives little away as we could have mild and wet in a south westerly or calm under the high with warm afternoons although as expected colder nights under the anticyclonic ECM.

  

Of course these only highlight the different outcomes in the weather and doesn't help in deciding which is the more likely solution.

Reading those graphs though the ECM Op run in week 2 looks more of a dry and calm result against many of the other members and conversely the GFS Op run seems overly unsettled being towards the top end of it's suite.

Now looking at day 10 mean 500hPa charts for the same time from both and we can see the middle way projection

 

which sort of reflects what I read in those graphs.

As ever probably something in between will turn up with some ridging and the north and west seeing the more unsettled regime.Pretty typical stuff for October by the looks.

 

 

[Frosty.]

Temperatures are expected to rise above average during the first half of october with either a long draw swly tropical maritime airflow or a drier continental flow sourced from Southern Europe / North Africa..or a combination of both. It also looks like the northwest of the uk will have the wettest and windiest weather with the southeast having the best weather between occasional rainbands...so, something like the Ecm 00z is possible!

Edited September 26, 2016 by Frosty.

[mb018538]

Big differences showing up again on the 12z...

GFS:

UKMO:

 

Much more settled UKMO run, GFS runs with the unsettled theme right through the run...

[Faronstream]

2 hours ago, blizzard81 said:

But this is what the GFS was showing on most of it's operational runs for the same time frame. ECM now jumps on board only for GFS to jump ship - a familiar tale. I expect GFS to climb back on board soon. A fine, warm first half to October beckons.

Well the last 6 days in longe range forecast either GFS or ECM has shown any signs of a new powerful high pressure, only deep depressions, weird to see that change within just 2 days, i still belive in average/ slightly below average temperatures as we go into October

[Frosty.]

Well isn't that just typical, just after I said the first half of october looks like bringing predominantly above average temperatures, along comes the Gfs 12z with hardly any warm weather to speak of.. that will teach me!

Anyway, it's an unsettled outlook with a fired up Atlantic producing low after low targeting the uk with barely any respite according to this run..it would certainly feel like october with even a risk of a polar maritime incursion. I like to see the arctic cold building at this time of year and hope we don't have a repeat of that winter from hell.

[Paul]

For those who may not have seen it yet, Matt's synoptic guidance for the week ahead is here. 

http://www.netweather.tv/index.cgi?action=news;storyid=7670;sess=

[blizzard81]

1 hour ago, Faronstream said:

Well the last 6 days in longe range forecast either GFS or ECM has shown any signs of a new powerful high pressure, only deep depressions, weird to see that change within just 2 days, i still belive in average/ slightly below average temperatures as we go into October

Many of the GFS operational runs over the weekend were showing dry, warm anticyclonic conditions with southerly winds from around the 4th October onwards. ECM has come onboard today. The GFS will climb back onboard after it's predictable 24 hour wobble!

[Singularity]

  

Significant differences with the behaviour of LP at the weekend; GFS has it on a track that's both slower and further south than ECM and UKMO (with UKMO barely developing it anyway).

  

The impacts on the evolution going forward are stark; the slower solution from GFS causes the low to 'hang back' and effectively block the attempts of an amplifying ridge to build through the UK. Not only that, but the low keeps the door open for the next feature in the Atlantic to muscle in. By contrast, ECM and UKMO allow the high to take control, albeit ECM more slowly than UKMO.

Looking kind of warm again from ECM by days 7-8, though the angle of the Atlantic trough is less favourable for both importing the warm air and sustaining such an airflow. The 00z was truly extraordinary in this respect (on a par with the sensational spell of weather late Sep-early Oct 2011).

[Singularity]

Well, that's what a very negative Arctic Oscillation looks like, if anyone was wondering...!

It's also a great (mock) example of how a vortex disintegration doesn't always work out well for the UK; it's all aboout where the residual 'lobes' end up. Not that this example starts off with a developed vortex in the first place - it just resembles a broken down one in the latter stages.

Edited September 26, 2016 by Singularity

[Frosty.]

There is a chance of an mini october unseasonably warm spell according to the Gfs 00z and even warmer Ecm 00z...

 

 

Edited September 27, 2016 by Frosty.

[phil nw.]

It looks like another sub tropical low develops around the Florida peninsular and by the end of the week it's showing moving ne as it rides the jet stream.This track and development of this feature is what the models are still coming to terms with as it impacts any ridging ahead of it.

Here are 3 images showing its growth and track as seen by the GFS at days 1,4 and 5.

Quite an innocuous feature to start with just moving off Florida with surface pressure at 1012mb but see how it deepens as it contacts the Atlantic jet as it moves first north and then east across the Atlantic.Images from Tropical Tidbits.http://www.tropicaltidbits.com/

  

  

At the moment it is modeled as quite a deep feature just to our west by the weekend pulling in another burst of warmth from the preceding ridging with the ECM slower to push this away.

 

so next week could start quite warm and bright in the south east if the ECM proves to be correct but with a now more active jet it doesn't look like lasting more than a couple of days.

 

 

[damianslaw]

1 hour ago, Singularity said:

Well, that's what a very negative Arctic Oscillation looks like, if anyone was wondering...!

It's also a great (mock) example of how a vortex disintegration doesn't always work out well for the UK; it's all aboout where the residual 'lobes' end up. Not that this example starts off with a developed vortex in the first place - it just resembles a broken down one in the latter stages.

Thanks for posting this image, good to see the overall pattern over the northern hemisphere, and as you say its quite a blocked one, with a very fragmented weak PV. Traditionally the polar vortex gathers strength and depth through October, so will be interesting to see how long such a set up lasts.

 

What we have seen during September is significant warm air advection deep into the Pole which is a possible reason for the strong heights there at the moment, low pressure systems over the atlantic have come unstuck against significant ridge development.

 

Back to the models, lots in the air, ex-tropical storm systems once again coming into play by the weekend, making for large uncertainty. A cool down of sorts is on the cards for Thursday and Friday. ECM keen on building a ridge ahead of the next tropical storm system, GFS less so. The pattern of the last 6 weeks has been the strong ridge development with a highly ampliifed flow, however, the jet has much more gusto to it now and I suspect any ridge development that may occur will be much weaker affair preventing long drawn southerlies and plume event. We shall see.

[knocker]

The anomalies this evening are all in pretty good agreement with strong ridging Alaska and eastern North America with a deep trough mid Atlantic so just sticking with the EPS.

The upper flow from the SW (including the jet) portends systems tracking NE and impacting the west and NW of the UK again leaving the SE drier and fairly warm. As we move into the ext. period this may briefly improve as the trough weakens and becomes positively tilted we could see the HP influence extend a tad.

 

Edited September 26, 2016 by knocker

[mb018538]

Morning

GFS and UKMO looking more in agreement today - high pressure hanging on in the SE, lower pressure still effecting the NW at times. GFS turns on the blowtorch by day 10, with 850s up around 15c once more....





This has cropped up a few times now in different runs, so I guess it's not totally out of the question (if unlikely at this stage).

[knocker]

Quite interesting looking at the latest EC32 means update and what is striking, to me any way, is the rapidity of change of the upper pattern in the near future.

For example next Sunday sees low pressure dominating from the western Atlantic through to Scandinavia with a deep low SE of Greenland. But two days later this has morphed into highly amplified meridional pattern with the Atlantic trough edging east and strong ridging to the east of the UK. This effectively backs the upper flow to the SW quadrant which surface wise will push Atlantic systems on a more NE track but also introduce some warmer air particularly for the south and east.

But this amplification is very brief and almost strait away it starts weakening with the trough dissipating and becoming positively tilted which is not bad news for the UK  with positive heights to the east connecting to the Azores HP, And although the upper flow is once again veered towards the west the UK is generally under the influence of the aforementioned HP and temps still perhaps a little above average in the south.

So in summation. Unsettled this week leading to some interesting surface developments beginning of next week which I suspect the models may struggle with vis timing and then perhaps some more benign days.

Edited September 27, 2016 by knocker

[knocker]

And the brief scenario

[Frosty.]

The Gfs 00z shows some summery charts this morning, you could add a few degrees celsius to these figures and we would be looking at 23-24c max in favoured spots during the second week of october..nice

[Frosty.]

The Ecm 00z also shows a late taste of summer next week, at least for the s / se with temps potentially into the mid 20's celsius, it's similar to yesterday's 00z and much better than last night's 12z.

Edited September 27, 2016 by Frosty.

[knocker]

Wet and windy in Scotland Thursday and then the amplification which the ecm is hanging on to longer than previously indicated.

[Polar Maritime]

Ground/Air frosts for some by the weekend as a cool Pm flow pushes S/East Friday night.

Edited September 27, 2016 by Polar Maritime

[knocker]

The EPS is currently indicating that once the amplification at the beginning of next week wanes the rest of the week, including the weekend, could be quite reasonable apart from maybe the north west.

[Frosty.]

We are on track for temperatures to rise at least slightly above average next week and even warm across the s / se with temps into the low 20's c or perhaps even mid 20's c which would be in line with the Ecm 00z..The s / e also look like having longer fine spells by next week with the northwest corner bearing the brunt of the wind, persistent rain and showers..and lower temps.

And let's not overlook tomorrow which looks fine and warm across southern uk with temps up to 22/23c in the south / southeast.

[Faronstream]

58 minutes ago, Frosty. said:

We are on track for temperatures to rise at least slightly above average next week and even warm across the s / se with temps into the low 20's c or perhaps even mid 20's c which would be in line with the Ecm 00z..The s / e also look like having longer fine spells by next week with the northwest corner bearing the brunt of the wind, persistent rain and showers..and lower temps.

And let's not overlook tomorrow which looks fine and warm across southern uk with temps up to 22/23c in the south / southeast.

Don't forget that GFS still does not agree with ECM's solution,and for a week before sunday it was showing depression domination for most of west eujrope but has suddenly changed, i have never seen such a big change in the models for 6 years

Now i think it is too late for any high pressure if you want real heat, i would rather have this setup during the summer

[andymusic]

12 minutes ago, Faronstream said:

Don't forget that GFS still does not agree with ECM's solution,and for a week before sunday it was showing depression domination for most of west eujrope but has suddenly changed, i have never seen such a big change in the models for 6 years

Now i think it is too late for any high pressure if you want real heat, i would rather have this setup during the summer

usual problems at this time of the year with ex-tropical storms coming or not coming our way lol - difficult one for all the models to pin down