model discussion Model output discussion 11th July onwards

[carinthian]

Looks like a week of unsettled Autumnal conditions for Blighty. See that Son of Sam is now making an appearance in Mid - North Atlantic  forecast charts. Hurricane Sam has not made the usual track up close to the US East coast but rather meandering out in the North Atlantic. As we know to well these old tropical storms can throw a spanner into modeling around 144t and beyond. Its track and eventual positioning , I think is still to be grasped with, especially with an active polar front established and a jet predominately north of west to confront.  I would expect quite a few changes in the medium term  model outputs with its handling, but in the longer term, I favour a ridging of pressure eventually over Europe and possibly Southern Britain with a flip back to more settled condition, especially in Euroland.

C

[Cambrian]

Oz ECM and GFS operational runs this morning don’t seem to be indicating that ex- tropical Sam (I think that’s him!) is going to help to settle it down for us much through next week, suggesting that though it’s not going to be quite as cyclonic as the next few days, it still looks like we’ll still be under the influence of low pressure, indeed the ex-trop itself, and we all know how much moisture can be embedded in these systems. 

ECM has it bearing down on us by 192h but a lot of rain in that southwesterly fetch, the accumulated total precipitation for 120h and 240h show that the rainfall (as is often the case the ECM is really going for it!) is substantial between days 0-5 and also days 6-10, as pointed out by others, anything from 100mm to over 200mm in the next 10 days. 

  

 

The GFS at 192h is building the high further south compared with yesterday, allowing the Atlantic low, although further west than ECM, to send successive bands of wet stuff our way, again resulting in substantial totals, though as usual, not as high as the ECM, still high in general with over 100mm in many western parts and still piling up.

  

[johnholmes]

1 hour ago, Ed Stone said:

Well, well, well, well, well. Doesn't this morning's GFS 00Z run look eye-wateringly fantastic? No? I thought not!

    

    

   

Meanwhile, all is not revealed:

  

And, finally, the piece de resistance, the Met's 10-Day forecast:

 

Yet again a first class explanation, as one would expect, from a Met forecaster. Well worth watching.

 

[Frosty.]

The longer term ECMWF 0z ensemble mean suggests more of a north-south split with the south trending more towards settled and warmer whereas the north, especially the far north continues to be changeable / unsettled and cooler…broad brush as it’s the mean. 

[Frosty.]

As I described above regarding the longer term ECMWF 0z ensemble mean, likewise / ditto…  the GEFS 6z mean also eventually indicates a north-south / northwest-southeast split longer term with the south / southeast becoming more settled compared to the more changeable / unsettled conditions further north.. northwest?…I think the south will settle down between early / mid October and possibly beyond  with some sunshine but with overnight / early morning fog…unless further ex tropical storms have other ideas?!  ️ ? 

 

Edited September 30, 2021 by jon snow

[carinthian]

3 hours ago, carinthian said:

Looks like a week of unsettled Autumnal conditions for Blighty. See that Son of Sam is now making an appearance in Mid - North Atlantic  forecast charts. Hurricane Sam has not made the usual track up close to the US East coast but rather meandering out in the North Atlantic. As we know to well these old tropical storms can throw a spanner into modeling around 144t and beyond. Its track and eventual positioning , I think is still to be grasped with, especially with an active polar front established and a jet predominately north of west to confront.  I would expect quite a few changes in the medium term  model outputs with its handling, but in the longer term, I favour a ridging of pressure eventually over Europe and possibly Southern Britain with a flip back to more settled condition, especially in Euroland.

C

Yes, I know its another run and variation. As highlighted above the end action of ex Hurricane Sam is far from determined. That chart below from GFS at day 10 produces what must be the widest Euro/Asian ridge ever seen. Just follow the 1020mb isobar perimeter and you will see what I mean ! 

C

[damianslaw]

5 hours ago, mb018538 said:

ECM Op actually looks quite close to the NOAA chart above too. Sort of a halfway house - not completely flat, but nowhere near as amplified as some previous runs from 1-2 days ago.

Just look at this ECM rainfall chart for the next 10 days too. What a massive NW/SE split! Hills in Wales and NW England seeing eye watering totals over 200mm, so flooding definitely likely there.

Once again a flip from very dry to very wet here . Theme of the year.. the switch very sudden.

[damianslaw]

2 hours ago, jon snow said:

The longer term ECMWF 0z ensemble mean suggests more of a north-south split with the south trending more towards settled and warmer whereas the north, especially the far north continues to be changeable / unsettled and cooler…broad brush as it’s the mean. 

Very standard October fayre.. could be a very wet October in the NW if continues..

[Frosty.]

Looking towards mid October and possibly beyond, anyone who doesn’t like wet and windy should be happy with these charts from the GEFS 6z?!    

 

[Zenarcher]

Hey everyone, here's the most recent 10 day outlook using the averaged model charts,

Friday will be a windy day over the UK and the rain will clear away for many, leaving a combination of sunny intervals and showers, although heavy, perhaps thundery rain will continue in western Scotland. Saturday will start out sunny, but it will quickly turn windy, with more heavy rain or showers later in the day. Sunday appears to be another unsettled day; high gusts and extended periods of rain are expected in Scotland, but it should be drier farther south, with sunny spells and showers, but it will be windy there too.

  

While the wet and windy weather on Saturday and Sunday is getting the majority of the focus right now, a low pressure system will be moving near Scotland on Friday, bringing gusts of 50 to 60 mph to the Western and Northern areas, as seen below by the GFS and ECM.

 

Onto Saturday and Sunday there's still some uncertainty about where the heaviest rain and strongest winds will be. The models are mostly in agreement that the low pressure will be over Scotland on Saturday night, but how deep it'll go and the exact path it takes is still uncertain. What we do know is that it will be wet and windy for many places. So, what kind of wind gusts are we looking at? According to the ECM, inland gusts will reach 35 to 45 mph for the majority of the country, with exposed areas reaching 50 mph and 60 mph and along coastlines. Here are a few charts from the ECM from 4 pm on Saturday to 7 am on Sunday. However, bear in mind that as we move closer to Saturday, this will most likely change, so keep an eye on the most up-to-date forecast nearer the time.

  

Most areas will receive at least 20 to 30mm of rain over the next five days, according to the ECM rain accumulation chart, although Western and Northern areas might receive 50 to 100 mm,

Looking ahead to next week, Monday will be less windy to start with along with some sun and showers, but later in the day another low pressure system may develop, bringing more rain and wind, primarily to the south, but it's tough to tell how much rain and also how strong the wind will be at this moment because the models are still in disagreement. Wednesday will remain unsettled, but a ridge of high pressure could form across the South on Thursday, bringing with it the possibility of drier and more calm weather for a while. We also have ex hurricane Sam moving into the Atlantic on Tuesday, which is something to keep a close eye on. Models are still divided on the track, so there's still a chance it could affect our weather by bringing more wind and rain later next week, but for now, most models keep the ex hurricane out in the Atlantic near Greenland or Iceland.

   

By next Friday and into the weekend, the models are still predicting some high pressure across the South of the UK, keeping drier and settled weather there, but the Northern half of the country will remain unsettled. You can see on the charts below where all the models place the ex hurricane Sam in the Atlantic, some close to the UK and others further out West, demonstrating that where it ends up affects our weather for later next week.

  

Edited September 30, 2021 by Zenarcher

[Frosty.]

Looking at the ICON 12z, there’s something of a northwest-southeast split develops from around T+144 hours onwards with the SE becoming drier and warmer, indeed temperatures recover widely once winds switch southwesterly but before then we are pretty much all in the same unsettled boat with generally below average temperatures.

[Methuselah]

Karl's been looking at the IKON: 

[mb018538]

ukmo and gfs looking very different at 144 hours. Lots to be resolved still.

[Methuselah]

Not a bad position for an anticyclone, even if it's October and prone to morning fog (good for @lassie23)? Clearly less-warm than previous runs but, hey, who's complaining?

    

[Cambrian]

Big run-to-run variability from the GFS. The 12z operational bubbling up a high pressure for us by days 8 / 9 / 10, looks a lot more promising for something drier pushing itself up from the south. So a similar trend is trying to work its way in on most GFS runs, but the timing varies a lot.

  

 

[Methuselah]

Were these charts to be for late January/early February, and Uppers were -15C (instead of 0-1C) I'd be wetting myself with excitement. But, alas, it's not. It's sodding October!

    

    

It's a sickener! 

Edited September 30, 2021 by Ed Stone

[Frosty.]

The GEFS 12z mean improves considerably just beyond a week from now which is reflected by some much more settled and warmer perturbations!

 

 

[lassie23]

52 minutes ago, Ed Stone said:

Not a bad position for an anticyclone, even if it's October and prone to morning fog (good for @lassie23)? Clearly less-warm than previous runs but, hey, who's complaining?

    

October fog index seems to come round quicker and quicker. Getting off to a shocking start.

[booferking]

Hopefully the early signs of an front loaded winter

[Frosty.]

Don’t all rush to comment on the ECMWF 12z operational! …for sure it’s a generally unsettled run with below average temperatures…until an ex tropical storm changes that and tropical maritime air pumps NE right across the u k…..however, any tropical storm makes the mid / long term outlook very uncertain but can / could precipitate some fine unseasonably warm weather for the u k?. 

 

[Cambrian]

ECMWF 12z operational !

And then Big Bad Sam said “I’ll huff”…..

+72h

 

“And I’ll puff”….

+144h

 

“And I’ll get subsumed in your upper-level trough”

+216h

[Mike Poole]

22 minutes ago, Cambrian said:

ECMWF 12z operational !

And then Big Bad Sam said “I’ll huff”…..

+72h

 

“And I’ll puff”….

+144h

 

“And I’ll get subsumed in your upper-level trough”

+216h

Yes, I was always very sceptical that this ex-tropical storm would do anything for the UK, other than push up a ridge ahead of it.  

Earlier, consensus now forming over a more northern track of the deepest low at T72, ECM has it north of Scotland now:

Potent low at 965 hPa, but for most will just be a moderately windy and wet day.  

[damianslaw]

Uncertainty how ex tropical storm Sam will interact with the jet. We have a very deep long wave trough over the UK now, and there is every chance the storm will be scooped up into the trough, any downstream ridge a very temporary feature resulting in a prolonged very disturbed spell with heavy rain, wind and temps no better than average if not a bit below in north, only se parts seeing anything a bit warmer.

[Mike Poole]

I know some posters on here have said normal Autumn fayre to come…but really, ECM T240 shows anything but I think:

A - you have this massive ridge from UK to beyond Siberia, @carinthian alluded to this earlier.

B - there’s no driver of unsettled weather from the US either.  

C - there’s an Arctic high.  

What little of the vortex there is still shows (probably) a broadly 5 wave pattern.  I cannot see a very unsettled autumn for the UK out of this, but it will be well into November before cold patterns emerge, and then, a front loaded winter pattern will ask the question, where is the cold air?  

[Don]

5 minutes ago, Mike Poole said:

That’s the issue with the lack of cold air to tap into.  A front loaded winter with cold rain in the south?!  No thanks, what a waste!

Edited September 30, 2021 by Don