Model output discussion - August hot spell - how hot, how long?

[Mike Poole]

Early update on the 12z, here’s ICON, GFS, GEM at T180, probably at the outer bounds of the reliable, showing high pressure moving across the south of the country, won’t be especially warm, given time of year and position of the high, but settled, yes.

So a pleasant set up for second week in September.

[Frosty.]

I’m probably in the minority, a bit like the GEFS 12z members but I still think there’s a window of opportunity for high pressure to gain a foothold, at least across southern parts of the u k..for a time at least which would mean a spell of pleasantly warm and fine weather with sunny periods and light winds but some chilly nights..however, looking further ahead towards mid September there’s currently strong support for a more generally unsettled period, especially further n / nw..all in all it’s not unusual, it’s fairly typical for early autumn...

Edited August 31, 2020 by Jon Snow

[Mike Poole]

ECM and JMA at T192:

So we have a settled high pressure over the southern UK, consensus on this now, but the wind not coming from a warm direction.  And after?  The models tend to go down hill in FI, but CFS AAM predictions (reliability issues, I know) are for a big rise from this point on, we will see...

[Captain Shortwave]

The story of the next ten days appears to be repeated attempts for the Azores high to ridge towards us, but it seems to be pulled back westwards pretty quickly. Winds generally from the west with temperatures probably close to normal on balance. Unfortunately I suspect the warm sectors will carry a lot of cloud, more so than in mid-summer where the pressure patterns and 850s could deliver temperatures in the mid/high twenties in the east. Not so now really. However conditions do look considerably drier for many.

Edited August 31, 2020 by Captain Shortwave

[Mike Poole]

56 minutes ago, Captain Shortwave said:

The story of the next ten days appears to be repeated attempts for the Azores high to ridge towards us, but it seems to be pulled back westwards pretty quickly. Winds generally from the west with temperatures probably close to normal on balance. Unfortunately I suspect the warm sectors will carry a lot of cloud, more so than in mid-summer where the pressure patterns and 850s could deliver temperatures in the mid/high twenties in the east. Not so now really. However conditions do look considerably drier for many.

Yes, that is backed up by the ECM mean, here T192 (actually a decent signal here with 1025 widespread on the mean, this should now happen) with the high across southern UK, and T240 when it is pulled back:

The T240 picture might yet improve if AAM rises as predicted?

[Mike Poole]

A positively tilted losenge from the Azores on the GFS pub run T162:

Nice! 

Edit, and by T186 across the whole south, as most other models predicting:

\

Edited August 31, 2020 by Mike Poole

[MP-R]

For balance, this would certainly blow some of the omnipresent cobwebs away!

[mushymanrob]

I was hoping the positive pressure anomaly to our west would progress eastward... sadly this doesnt appear to be the case if this chart is accurate. A strong Azores high just west of the Azores, troughing centred over Iceland, a mean upper northwesterly = cool and unsettled although not overly wet , below average?..

 

[mountain shadow]

No Indian Summer on offer with a very cool blustery North Westerly in the offing in a week or so.

The eternal Autumn continues.

[mb018538]

18 minutes ago, mountain shadow said:

No Indian Summer on offer with a very cool blustery North Westerly in the offing in a week or so.

The eternal Autumn continues.

Yes....sadly the runs of a couple of days ago have vanished, any any build of pressure looks fleeting before the high disappears out into the mid Atlantic and allows a trough to dominate again. Still no sign of anything particularly warm and settled on the horizon.

[wellington boot]

As before, it doesn't look particularly warm, but at least for the South it looks generally dry and settled for much of the next ten days. 

It is also noticeable that there seems to be almost unanimous agreement right now that an enormous LP will sweep in on day 10 precisely. However, when have the models ever had a unanimous lock on day 10 developments...? You have to assume this will change and evolve as we go along, and if AAM really goes sharply positive by mid month, then anything is possible...

[mb018538]

1 hour ago, mb018538 said:

Yes....sadly the runs of a couple of days ago have vanished, any any build of pressure looks fleeting before the high disappears out into the mid Atlantic and allows a trough to dominate again. Still no sign of anything particularly warm and settled on the horizon.

As said - we've seen a bit of a flip the last couple of days. Looks like we're going to miss out again for now, and anything decent is going to have to wait until much later in the month.

[mountain shadow]

16 minutes ago, mb018538 said:

As said - we've seen a bit of a flip the last couple of days. Looks like we're going to miss out again for now, and anything decent is going to have to wait until much later in the month.

I thought the AAM signal was for it to increase? I wonder what has scuppered it this time?

There was a continued forecast for AAM to increase throughout the Summer but it never happened. I wonder what has been overriding the signal?

[jules216]

1 hour ago, mountain shadow said:

I thought the AAM signal was for it to increase? I wonder what has scuppered it this time?

There was a continued forecast for AAM to increase throughout the Summer but it never happened. I wonder what has been overriding the signal?

Unsettled weather in the UK/Ireland is September is well within the expectations of emerging weak La Nina analogs. The largest anomaly is the persistent high pressure centered over Baltics/East-Central Europe. The CFS weeklies rather nicely match the analogs even on the hemispheric view. Fast forward to November and it will look a lot more interesting

[mb018538]

1 hour ago, mountain shadow said:

I thought the AAM signal was for it to increase? I wonder what has scuppered it this time?

There was a continued forecast for AAM to increase throughout the Summer but it never happened. I wonder what has been overriding the signal?

Nothing has really changed in that regard - it is still forecast to increase sharply towards mid month. Sadly like all teleconnections - AAM isn't a silver bullet, and doesn't guarantee settled weather here. It just increases the odds, but the pieces can still fall in the wrong place. The remnants of ex Laura and now TD15 heading into the mid latitudes doesn't help. It may smooth out and settle down in the 10-15 day period.

Edited September 1, 2020 by mb018538

[johnholmes]

Tuesday 1 September 500 mb anomaly charts update

Ec-gfs and both show similar +ve height rises off eastern seaboard e to nw Europe/uk area; this is the second day such a pattern has been shown, prior to Sunday and neither showed this.

Noaa has very slight height rises prior to this, in particular Sunday showing +90 DM from s of Newfoundland out into Greenland. 90 DM is about the first time that, if it is maintained, it is worth starting to watch subsequent charts. This has duly occurred with a spread of +ve height rises up to 150 DM, from the Newfoundland area across the Atlantic to western sw Ireland showing about 90 DM. The actual contour chart showing, slight divergent anticyclone curvature would suggest, if this remains, that a surface high MAY start to develop off SW Ireland, possibly an extension of the Azores ridge. So looking at the 3 charts this morning I would be expecting some decrease in the changeable pattern towards the weekend, especially for SW’ern areas, tempered by the 8-14 backing away from this and showing very slight –ve height falls coupled with the contour flow reforming into an overall trough pattern over the uk area.

As I often stress, using the anomaly part of these charts is incredibly hard to be objective and in my view, no disrespect to anyone are best not used as the main feature until you have a lot of experience with these charts. Use the contour predictions and again look for continuity in each model over say 3 days and a similar chart between all 3 models. Then there is I feel about a 70-75% probability of that upper air pattern being what the synoptic models will increasingly show in the 6-10 day period. Remember though they are mean charts so individual days may not be quite the same. It is unlikely though that there will be a marked difference. For example a very marked trough-ridge chart is unlikely to suddenly become a flat westerly and vice versa. Sorry to go on but I was asked a question about them so have tried to incorporate the reply in this daily analysis.

Finally re IMBY, rest assured, unless I specifically refer to this in a post, it will never be how I attempt to do a forecast.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

https://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

 

[Daniel*]

5 hours ago, mb018538 said:

Nothing has really changed in that regard - it is still forecast to increase sharply towards mid month. Sadly like all teleconnections - AAM isn't a silver bullet, and doesn't guarantee settled weather here. It just increases the odds, but the pieces can still fall in the wrong place. The remnants of ex Laura and now TD15 heading into the mid latitudes doesn't help. It may smooth out and settle down in the 10-15 day period.

I don’t understand it’s settled now September has started nicely. ECM forecasting 12mm over next 10 days in London so really quite dry, it does look near average or even bit cooler, probably more so by night. It definitely looks better for east the outlook at least out to semi reliable 6-10d seems quite good. AAM is currently very -ve now and we’re seeing pleasant weather so as you say, careful interpretation should be made with other factors.

[Ice Day]

Just looking at tonight's runs, the ECM and GFS are certainly on the same page at 168 with the UKMO looking like it's heading in the same direction, should be a pretty warm day next Tuesday for the bulk of the UK.

     

Warmth slipping south at 192 though

   

... and by 216, warmth heads north again.  A wax and wane pattern overall - typical early autumn fayre!

  

 

[Mike Poole]

24 minutes ago, Ice Day said:

Just looking at tonight's runs, the ECM and GFS are certainly on the same page at 168 with the UKMO looking like it's heading in the same direction, should be a pretty warm day next Tuesday for the bulk of the UK.

     

Warmth slipping south at 192 though

   

... and by 216, warmth heads north again.  A wax and wane pattern overall - typical early autumn fayre!

  

 

Yes, I was just going to post then T168 charts, it is after that that things diverge.  GFS goes on to bring in some settled warm weather in FI, GEM goes unsettled, and ECM retrogressive the high back into the Atlantic.  

With AAM rising even in the reliable, I wonder if when we actually get to a week today, the outlook looks more promising going into the following week:

[Frosty.]

Call me a cherry picker..  .I don’t mind, I’ve been called worse but I really like the way the Gfs 12z operational ends and it’s actually well supported by the GEFS 12z too!..however, it’s early autumn now and it’s the Atlantic v Azores High, both slugging it out with each gaining the upper hand at times but I now fancy mid September may turn out better than I was thinking yesterday..of course tomorrow could be completely the opposite but that’s for another day!!

[damianslaw]

Into the quiet month of September, not many posts today as well. Models show a broad westerly pattern in the reliable with the azores high trying to ridge NE but not sufficiently enough, hence we are left with typical atlantic flow around it, temps near average for early September, something cooler for the north by the end of the week as we see more of a NW flow. A fairly decent outlook after tomorrow for central, south and east parts with lots of dry usable weather, further NW showery but no washout.

Into next week, differences between the models, GFS wants to ridge the azores high NE, ECM pulls it out west and we are then exposed to a deep longwave trough anchoring down from the NW, cool and unsettled. GFS was showing cool unsettled conditions as well for next week. Too early to call how things may pan out. 

Overall a very very average picture.. 

[Mike Poole]

As you were on the pub run at T168:

But seems reluctant to retrogress the HP as far west and leaves a sliver over the UK, not the first run with this I’ve seen.  T216:

Worth watching to see if this develops into a more settled warm pattern in days to come...

[Scorcher]

I'm surprised there's so little comment this morning- unless my eyes are deceiving me there has been a notable improvement in the output this morning from the main models. The high for the middle of next week looks further north on this morning's runs- perhaps allowing for more widespread sunshine?

Looks to me like Wednesday has the potential to be a very warm day and possibly Tuesday too, although cloud may be more of an issue on Tuesday.

 

[summer blizzard]

Yes, the Euro largely pushes off the trough influence to day 9. 

[wellington boot]

18 minutes ago, Scorcher said:

I'm surprised there's so little comment this morning- unless my eyes are deceiving me there has been a notable improvement in the output this morning from the main models. The high for the middle of next week looks further north on this morning's runs- perhaps allowing for more widespread sunshine?

Indeed, was wondering the same myself. Just haven't had time to comment on it! The whole run looks decent and generally settled for the South and next week looks promising for all parts.

6 minutes ago, summer blizzard said:

Yes, the Euro largely pushes off the trough influence to day 9. 

As I commented yesterday, even remarkably close ten day chart agreement among models was very unlikely to stay that way, and indeed this morning ECM doesn't just push trough influence back to day 9 but the trough barely registers south of Yorkshire and by day 10 HP appears to be building back in.

Plenty to feel optimistic about over the next couple of weeks.