Model Output Discussion - Autumn arrives

[damianslaw]

46 minutes ago, Kirkcaldy Weather said:

If there are any people that are new to watching the models hopefully this post can help with understanding a few bits, often weather systems downstream can have a big role in the weather upstream which is what we see in the short term.

Hurricane fiona now in the process of the phasing that I mentioned and likely she'll be the lowest pressure ever recorded in Canada.   here I've marked the movement of Fiona and how that then promotes the ridge which allows the low to the north to move south with the cooler air. 

There's a warm sector just ahead of the cold front as I've marked here 

 

the coldest of the air gradually fizzling out but low pressure the overall dominating feature so showers and a cooler feel which is pretty fitting to the season of Autumn

 

Also just wanted to say,I've seen the word 'zonal' begin to show up in here which isn't really accurate for any of the current output, go back and look at the charts from winter 2013/14 the barrage of storms that's a true zonal pattern

 

 

Agree, it looks more cyclonic than zonal.

[Frosty.]

I think the GEFS mean is on to something regarding early October?, which incidentally ties in with Exeter’s current thoughts ..ergo, becoming less unsettled / more settled / benign / pleasant with mists and mellow fruitfulness a distinct probability.. at least across southern u k?… ps.. I love autumn, the changing colour of the leaves to yellow is wonderful!!!..or am I crazy  for saying that?.. too late now innit, it’s out there!! ️ 🌫 🐿  

 

 

Edited September 23, 2022 by jon snow

[Don]

2 hours ago, Kirkcaldy Weather said:

 

There's a warm sector just ahead of the cold front as I've marked here 

 

 

Oh gawd, the dreaded warm sector!!  Why is it they always tend to crop up these days when it comes to cold spells??!!

[I remember Atlantic 252]

15 minutes ago, Don said:

Oh gawd, the dreaded warm sector!!  Why is it they always tend to crop up these days when it comes to cold spells??!!

Only Sept! warm sectors not a problem surely

[Frosty.]

I’m basically ignoring the Gfs 12z operational as I choose to believe it’s an unsettled outlier!…the mean is more stable, as one would expect, it indicates a gradual settling down in the mid / longer term, especially further south following an initially more unsettled phase…so, I reckon early to possibly mid October could be rather benign / pleasant, at least further s / se…of course..I could be completely wrong, but then, I’m an amateur, so my opinion doesn’t matter..does it!

 

 

[Frosty.]

Quite an impressive day 10  ECMWF 12z operational..a kind of glimpse of the memorable summer just gone! …must say, I’m looking forwards now to a hopefully memorable winter, from a coldie perspective, call me deluded.. I don’t mind!!  

 

[Allseasons-Si]

The ECM ends nice...

at day ten.

Edit: @jon snow,...SNAP

Edited September 23, 2022 by Allseasons-si

[Don]

1 hour ago, I remember Atlantic 252 said:

Only Sept! warm sectors not a problem surely

It might only be September, but it seems to happen a lot in winter too these days!  It just served as a reminder lol!!

[Don]

1 hour ago, Allseasons-si said:

The ECM ends nice...

at day ten.

Edit: @jon snow,...SNAP

It would seem that a settled and perhaps warm spell of weather is on the way for October.  However, the models 'might' be bringing it in a little early as the latest Met Office 16-30 day forecast is suggesting an unsettled start to the month with it possibly settling down and warming up towards the end of the first week.

1 hour ago, jon snow said:

Quite an impressive day 10  ECMWF 12z operational..a kind of glimpse of the memorable summer just gone! …must say, I’m looking forwards now to a hopefully memorable winter, from a coldie perspective, call me deluded.. I don’t mind!!  

I wouldn't mind a 1995 repeat next month!  Not that I necessarily think that will be the case mind.

[Mike Poole]

5 hours ago, Kirkcaldy Weather said:

Also just wanted to say,I've seen the word 'zonal' begin to show up in here which isn't really accurate for any of the current output, go back and look at the charts from winter 2013/14 the barrage of storms that's a true zonal pattern

 

I have to agree strongly with this, a single low is not necessarily a zonal pattern, lows can crop up in all sorts of ways on the models, like we’ve seen since the end of summer, a long lasting cut off low, ex-tropical storms threatening but eventually not delivering.  Zonal means weather coming at us from the same latitude incessantly - and it does sometimes, but not this year, and actually not for most of the last two years.  For us it means from the west on a jet stream straight across the Atlantic, but the term zonal could actually equally be used for a barrage of systems from the east like March 2018.  

What I find fascinating this autumn, is there is just no sign yet of a proper line of systems coming across the Atlantic, and there’s good reason to think that there won’t be with that super warm patch of SSTs in the North Atlantic, possibly a symptom not a cause of the current long lasting weather pattern:

A ridge magnet, all other things being equal?  Which is why it is not surprising to see the odd potent northerly turning up on the model output now, GFS 12z FI (T360) for example:

I don’t see this general pattern shifting and giving way to normal autumn fayre, interesting synoptics to continue to show on the models would be my guess, with high pressure fairly close by for much of the time, but the position will vary…

Edited September 23, 2022 by Mike Poole

[Jordan S]

An update to my previous outlook post on Monday, and to be honest the most likely outlook for the end of the month through the first week into the second week of October is largely unchanged.

But there are a few smaller changes.

What hasn't changed..

1. Is the expected continuation of northerly/northwesterly winds across the country for the last few days of the month aswell as low pressure largely over the north sea producing the most showers over northern and eastern areas along with cooler than average temperatures.

2. A drier first few days of October across southern half of UK is still most likely along with changeable conditions expected to remain in the north, again with westerly winds returning.

I'm purposely using the 12z GFS below as I feel that shows the more likely placement of the high over southern areas, but either way, that update and this update still show the drier theme for the south just details differ as you'd expect a week away.

What HAS changed from my previous outlook for the end of the month...

One or two smaller disturbances expected to run east/southeast over the top of the large high to our west bringing the risk of more persistent rain/showers into the west and south.

What also hasn't changed I feel..

High pressure most likely to slip to our west/southwest through the second week of October, allowing the Jetstream and subsequently a low pressure dominated pattern to develop through the north Atlantic and more specifically close to across the UK, with a continued higher likelihood that this will be more a northwest to southeast alignment of the Jetstream and low pressures that cross the Atlantic and through the UK atleast for a time, especially again with higher pressure probably more dominant over northwestern parts of the atlantic with temperatures back up to around average and frequent rain, some of it heavy along with strong winds. Though again, the Jetstream periodically expected to become disorganized with northerly winds more likely than average during this second week, bringing the possibility of colder temperatures and more snow to Scottish mountains and possibly slightly lower levels too here, of course with this another high moving back to the west of us would take place to bring us those brief northerlies.

 

The last paragraph really a virtual repeat of what I said on Monday. But of course second week of October is a while away and a lot to get through synoptically speaking before we get to the second week of October.

[MATTWOLVES 3]

I think the Ecm has been rather poor for some time now....it appears it as backed down from the very unsettled conditions which were flagged up the other day! Yes next week could see some rain at times and strong winds also but beyond that it looks increasingly likely that High pressure will build towards the South and bring yet another settled spell.

The op now shows this scenario and it gets backed up by the mean with a fair few ens also going down this route. So at this stage the noaa looked pretty close to the mark.

For me cool misty mornings and evenings can be quite relaxing for October and I would much prefer that over relentless rain. But each to there own. But this morning i feel the trend is for an improvement to begin as we enter the new month.

So regardless of the conditions i bid you all a sterling Weekend. Stay happy and stay healthy.

Edited September 24, 2022 by MATTWOLVES

[Methuselah]

2 minutes ago, MATTWOLVES said:

I think the Ecm has been rather poor for some time now....it appears it as backed down from the very unsettled conditions which were flagged up the other day! Yes next week could see some rain at times and strong winds also but beyond that it looks increasingly likely that High pressure will build towards the South and bring yet another settled spell.

The op now shows this scenario and it gets backed up by the mean with a fair few ens also going down this route. So at this stage the noaa looked pretty close to the mark.

For me cool misty mornings and evenings can be quite relaxing for October and I would much prefer that over relentless rain. Bit each to there own. But this morning i feel the trend is for an improvement to begin as we enter the new month.

So regardless of the conditions i bid you all a sterling Weekend. Stay happy and stay healthy.

Indeed, Matt -- this year's October Fog Index might get off to a cracking start?

[Frosty.]

Hey guys, I may have mentioned this yesterday???..a few times.. nudge nudge.. wink wink  … ... ..but early-ish October May yet be quite benign / pleasant for many according to the GEFS 6z mean.. ️ 🌫  

Edited September 24, 2022 by jon snow

[Allseasons-Si]

Thanks @jon snow and @MATTWOLVES

Just a quick one whilst having dinner,there seems to be more of a pressure build through the UK as we enter October>>,here is a look at a few anomalies etc etc...

day ten EPS 500's/MSLP and temps

^and as you can see there are +ve anomalies through the UK with temps above average and backed up by the EPS clusters with the minority going for heights near the uk...

GEFS ens pressure graph showing a marked rise in pressure as we go into October too,...splendid

and finally the with direction from De-built,i have added the directions corisponding to the colors and as you can see,the majority go for S/SW winds backing W to NW at times

Green=N

Red=S

Yellow=W

Orange=SW

Light green=NW

the other colors are:-

Light blue=NE

Pink=SE

Purple=E

i always tend to look at these graphs towards the winter months to see if there is any sort of trend to a colder scenario

anyway,...that is me for now,enjoy the weekend all,...yes it is a bit cooler today in that N wind but get into a nice sunny position out of the wind and it's glorious

C U for now

 

 

[Frosty.]

Just before the 12z gets into full swing, a quick mention about the ECMWF 0z ensemble mean, for sure, there are good signs of a gradual settling down from the south longer term (early October) following an admittedly more unsettled / cyclonic late september / start to October! ️ 🌫  

Edited September 24, 2022 by jon snow

[stodge]

Evening all

Plenty of options on the table still for a week or so hence.

There's a strong signal for what could be called a reversion to normality with HP to the south, LP to the north and W'ly winds - whether the troughs and ridges are slightly more negatively aligned on some models than others is a matter of conjecture.

Not for the first time recently, ECM is on its own promoting more height rises to the north.

The 850 profiles from ECM and GFS OP reveal the rationale for the synoptic divergence at T+240.

[Guest]

Hello October.  Looks like we could see some typically wet and windy weather later in the week if the UKMO and ECMWF 00z runs are on the money.

 

GFS and GEM keep this low further north so still some disagreements but even they show rain and wind passing through.

 

[sheikhy]

Unsettled for a time next week but looks like high pressure could be moving pretty swiftly back in into october!!!

[damianslaw]

A chilly unsettled end to September on the cards. Definately an autumnal look to things. As we move into October models show a trend to more settled with the cool polar airstream cut off. All in all very typical conditions for the time of year.

The jetstream has more oomph to it right now but much of the reason for this down to the behaviour of ex tropical storm systems, and we are far from a zonal outlook.

 

Edited September 25, 2022 by damianslaw

[minus10]

Yes ecm 0z keen on a very unsettled spell next weekend with some decent rain i think even down here and very windy whereas gfs 0z not really interested in bringing that low in to impact us...

 

Ecm has some support from its ens and it has been rather consistent with this signal for a while..

....after that its mists and mellow fruitfulness...

[sheikhy]

Those mushynomalies could still be correct with high pressure over the uk between day 8 and 14!!!!

[Uncertainty]

There’s more momentum now in the idea that after next weekends low pressure traverses, high pressure could return (as it so often has recently).

 

First of all the signal is there and consistent in the noaa anomalies

 

 

 

The ECM op follows this neatly 

 

 

The GFS roots the heights slightly further south but the same general story being told.

 

 

The GEM is flatter and a disturbance sneaks over the top at day 9.

 

 

 

Though interestingly the heights still build eventually.

 

This suggests to me there is something driving this pressure build that the models have cottoned on to…

 

A look at the tropics suggests the mjo could be minded to head back to phases 4 and 5.

 

 

 

 

Using the September phase 4 and October phase 5 Nina composites, we can see some similarities to the suggested progression.

 

 

 

Obviously the high cyclone activity in the Atlantic complicates the above, particularly TS Ian which is eyeing up Florida as we speak. 
 

The JMA, for example, keeps the remnants of Ian languishing around the CONUS ( manifested here by the 1010mb low near the gulf).

 

 

This means the extra amplification in the Atlantic never occurs and a flatter pattern results. it does build eventually by day 14, adding to the suggestion that some kind of hp build is highly likely but the timing is subject to change.

 

Going back to the ecm day 9 chart, we can see the remnants of Ian amplifying the jet of the Eastern seaboard, adding to the meriodonality of the jet and increasing the waveheight of the U.K. ridge.

 

So the next 3 stages of the forecast are:

 

a) A colder period of northerly / NW winds until next weekend = almost certain

 

b) A strong developing low impacting the U.K. next weekend = likely, but track very uncertain 

 

c) Suggestions of renewed ridging near the U.K. = possible, but still only a suggestion at present.

 

Edited September 25, 2022 by Uncertainy

[Rain All Night]

1 hour ago, Uncertainy said:

So the next 3 stages of the forecast are:

a) A colder period of northerly / NW winds until next weekend = almost certain

b) A strong developing low impacting the U.K. next weekend = likely, but track very uncertain 

c) Suggestions of renewed ridging near the U.K. = possible, but still only a suggestion at present.

This summary at the end of your post is very helpful as it allows me to compare the conclusions I have drawn from reading your analysis with your own conclusions, which tells me whether or not I have understood the analysis correctly. Thank you!

[minus10]

Gfs 6z edging the weekend low closer compared to 0z...