model discussion Model output discussion 11th July onwards

[Summer8906]

14 hours ago, damianslaw said:

As others have said, quite abrupt changes in the models this evening, all courtesy of how they interact ex tropical storm Sam with the jetstream. All are showing the feature promoting a strong ridge ahead - and the jestream pulled away from the UK on a SW-NE trajectory far to our NW. 

Looking at the jestream profile, it looks quite messy longer term, suggestion it will loop in on itself, and strike through scandi, not surprised to see some of the longer range output suggesting heights eventually building NW, quite unusual, indeed very unusual for this to happen in October. It could be the models have it all wrong, and ex storm Sam fools them all.. but if the models verify as shown this eve, we will exchange the very disturbed conditions of now, much drier conditions, and feeling pleasant, but possibly chilly nights, before something more substantively colder possibly if we see the retrogression - relative to the time of year. Very interesting.

Talk of retrogression reminds me of 2010. As per this year, the first week of October was very wet and unsettled before sunny and warm weather arrived by Friday 8th. The high retrogressed and temperature gradually fell through the month, with wind backing from SE to E and later to N with a series of northerly outbreaks.

By coincidence, 2010 was the last year October began on a Friday.

[Frosty.]

I agree with Ed, the Gfs 6z operational shows a very decent fine spell beyond the current green snot, Atlantic fronts are pegged back and only really flirt with the far NW until deep into low res…couldn’t really ask for better if you’re a fine weather fan?  

[Seasonal Trim]

12 minutes ago, Summer8906 said:

By coincidence, 2010 was the last year October began on a Friday.

That's me convinced, another record breaking cold Winter coming up. Off to buy a sledge as we speak! 

Edited October 2, 2021 by Seasonal Trim

[Cambrian]

On the GFS 6z operational, ex-tropical storm Sam is hanging on in there in the Atlantic through to 360h, it does go through some splitting and recruiting every few days, its centre wandering around the northern Atlantic, setting up several days of good dry weather by pushing up a high over us at the end of next week.

Day 6

 

 

But Sam doesn’t give up, the remnants of the system are traceable in some form all the way through to day 15, and indeed instrumental in eventually bringing a succession of fronts and small systems our way later in week 2 as it deepens again in the mid-Atlantic, though this is well into the unreliable around day 12. There are indications of Sam’s eventual demise right at the end of the run. 

Day 12

  

I never said “Play it again, Sam”.

[Frosty.]

The GEFS 6z mean gradually becomes more settled during next week, especially across southern u k and in particular the SE with light winds, sunny spells and pleasant warmth although nights could be chilly with some mist and fog, perhaps only the far NW being the exception?…longer term, potentially a broadly northwest-southeast split which is quite normal for October.  ️ ?  

Edited October 2, 2021 by jon snow

[Cambrian]

As well as tricky old Sam, in the longer term, the models are grappling with anomalously high 850 hPa temperatures over northern Canada, and incursions of arctic air to the west of Greenland and down over Labrador, leading to temperature fluctuations and an occasional very modest pepping up of the looping jet, which is contributing to the long-wave stasis, playing an important part in determining to what extent we keep the mid-Atlantic trough. 

The interesting time is around day 8. Here is the T850 anomaly chart for day 8 from the 6z GFS op. The T850 is over 12 degrees above average for the time of year over eastern Canada.

Yesterday’s 18z GFS and the 0z ECM operational runs opted for a greater eastward transfer of the warmer uppers from the Canadian interior to the Labrador coast, the weaker jet diverted southward and westward then whips around to intensify and more or less cut off the low, contributing to the erosion of the Atlantic trough, the jet running east over the north of Scotland and fragmented thereafter. Hardly a remnant getting into mainland Europe. 

  

On the 0z and 6z GFS, for the same time a week Sunday, the arctic plunge off Labrador is maintained, keeping the broader loop in the jetstream, stopping the low getting cut off, and sufficient to maintain the trough in the North Atlantic, which then lives to fight another day.

  

[Methuselah]

Today's GEFS 06Z ensembles don't look too bad, to me: well within my comfort zone:

    

So, how warm will October turn out to be? Warm but nowhere near record-breaking is my guess!

Edited October 2, 2021 by Ed Stone

[minus10]

29 minutes ago, Cambrian said:

As well as tricky old Sam, in the longer term, the models are grappling with anomalously high 850 hPa temperatures over northern Canada, and incursions of arctic air to the west of Greenland and down over Labrador, leading to temperature fluctuations and an occasional very modest pepping up of the looping jet, which is contributing to the long-wave stasis, playing an important part in determining to what extent we keep the mid-Atlantic trough. 

The interesting time is around day 8. Here is the T850 anomaly chart for day 8 from the 6z GFS op. The T850 is over 12 degrees above average for the time of year over eastern Canada.

Yesterday’s 18z GFS and the 0z ECM operational runs opted for a greater eastward transfer of the warmer uppers from the Canadian interior to the Labrador coast, the weaker jet diverted southward and westward then whips around to intensify and more or less cut off the low, contributing to the erosion of the Atlantic trough, the jet running east over the north of Scotland and fragmented thereafter. Hardly a remnant getting into mainland Europe. 

  

On the 0z and 6z GFS, for the same time a week Sunday, the arctic plunge off Labrador is maintained, keeping the broader loop in the jetstream, stopping the low getting cut off, and sufficient to maintain the trough in the North Atlantic, which then lives to fight another day.

   ti

Yes i think it is a case of 'play it again Sam'   . Thanks Cambrian, I always find your posts informative and interesting. Quite an incredible meridional patten of which Sam is part thus ensuring on current output benign weather for us after this current unsettled spell (rain currently hammering down)...even fairly warmish days and possibly foggy nights. Latterly weather turning unsettled again but never really cold. 

Although t340 , jff, this is quite some longwave meridional pattern:

[Mike Poole]

ICON 12z at T180:

I rate this chart as highly unusual for this time of year, not the high pressure - that can occur at any time of year - but the lack of anything at all driving systems off the Atlantic, it’s been dead all year and still is.  

[Mike Poole]

UKMO T144:

I was musing yesterday about whether the low in the atlantic could be cut off.  Moot point today, follow the 1020 contour, it wraps around half the NH but it does look like it is cut off!  Or maybe the rest of the NH is?  I don’t know but this is seriously weird synoptics right now for the NH.

Edited October 2, 2021 by Mike Poole

[damianslaw]

7 minutes ago, Mike Poole said:

UKMO T144:

I was musing yesterday about whether the low in the atlantic could be cut off.  Moot point today, follow the 1020 contour, it wraps around half the NH but it does look like it is cut off!  Or maybe the rest of the NH is?  I don’t know but this is seriously weird synoptics right now for the NH.

Unusual I guess for October, not out of place after a SSW or in Spring. We've had a year with a weak diffluent jet.. Atlantic has never really stirred. Last time we had such a quiet Atlantic was 2010...

[Frosty.]

Just a quick mention about the JMA 0h before it disappears forever, the extended range showed some retrogression going on and just look at that bottled up arctic air waiting to flood south…this is just for my fellow coldies…where are you?…let’s be having you!    

 I do believe Delia has been drinking..  

 

[Northernlights]

On 02/10/2021 at 17:19, damianslaw said:

Unusual I guess for October, not out of place after a SSW or in Spring. We've had a year with a weak diffluent jet.. Atlantic has never really stirred. Last time we had such a quiet Atlantic was 2010...

Yes and what with the lag effect of solar minimum then we are at a similar point to 2010. For us too 2021  January to  early March was very cold /frosty  although snowfall was sporadic and did not always  ly but just a few miles inland from us there was significant snow from late December 2020 to  earlyMarch 2021 just like the winter of 2009/2010.

Was also one of the best winters for mountain snow for skiing which only a few hardy locals could access as the season could have lasted till end of May as April and May were so cold.

 

[Mike Poole]

26 minutes ago, damianslaw said:

Unusual I guess for October, not out of place after a SSW or in Spring. We've had a year with a weak diffluent jet.. Atlantic has never really stirred. Last time we had such a quiet Atlantic was 2010...

Yes, and you can see why various forecasters and members are musing about a front loaded winter.  2010 was before my time on here, unfortunately, I would have loved to be part of the discussion in the run up to that December.  

I think what we are seeing is a NH profile so blocked, that as wavelengths lengthen into winter, all the increased energy is going into reducing the meridional aspect of the flow, before it can get anywhere near a zonal flow.  For winter, we rely early season on cold pools in the right place, this is what I will be watching over the next couple of months, and it is a deal maker of deal breaker for December cold in the UK.  

Meanwhile GEM out to T162, and looks fine, big high pressure, same as the other runs:

[northwestsnow]

EC day 9 ...

 

[Mike Poole]

Any bets on an unsettled October based on ECM T240?

Thought not!  But the interest is what it means for winter…..

[Mapantz]

If members wish to discuss the coming winter, please head over to the thread below. Thanks. 

 

[Frosty.]

Well, the ECMWF 12z operational becomes very anticyclonic nationwide! made me think of the classic John Keats poem….

To Autumn

Season of mists and mellow fruitfulness,

Close bosom-friend of the maturing sun,

Conspiring with him how to load and bless,

With fruit the vines that round the thatch-eves run

etc..etc..wonderful!  

[Cambrian]

The GFS 12z op is firmly anticyclonic from day 6 to day 10. Likely to be a very pleasant period of Autumn weather. 
144h / 240h

 

The jetstream at 240h is typical of the latter part of this run, not really the jetstream as such - broken before Greenland, almost broken around the base of a very weak trough (very much on the wane on this run) from where it flows north to Iceland and then pretty much comes to a stop - a very weak form of meridional flow. 

The best the Atlantic can muster is a very tenuous trough of 1008mb into Ireland on day 12. 

Thereafter, it looks like the GFS is operating on the basis of a default ridging of the Azores high towards the UK and Ireland, a signature of the lack of energy in the Atlantic being captured in the models. Here at day 14, where there’s incidentally a little bit more life coming back into the trough as some colder air spills south out of the Arctic over Greenland. 

 

 

Edited October 2, 2021 by Cambrian

[Frosty.]

Now this is more like it, this is what I’m waiting for!  

 

[Ali1977]

First post of the Autumn for me, may as well start by looking at an a cracking FI chart. This one would certainly bring some early wintery conditions for higher ground in the North, potentially some lower ground looking at the inbound temps. It’ll be gone on the next run

[Frosty.]

6 minutes ago, Ali1977 said:

 It’ll be gone on the next run

Aye, but the anticyclonic outlook won’t!  

[Frosty.]

Looking at the longer term ECMWF 0z operational…it’s all that arctic air that interests me!…they do say the best route to cold is following an anticyclonic snooze?…fingers crossed! 

 

[Anthony Burden]

Hi first post this Autumn,pressure rise on the cards later next week both ECM and EFS shuffling 

the anticipated high pressure around.Depending on final set up could see some cold nights with

fog and frost possible.

[Anthony Burden]

PS. Sorry should be GFS.