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FI Charts ( T120+ onwards) Autumn 2023 **READ MOD NOTE IN FIRST

Gonzo

September now less than 120 hours away so time to open the FI Autumn 2023 thread.

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Mod Note:

This thread is for posting/discussing/analyzing FI CHARTS ONLY i.e. Charts in the unreliable time frame, generally +T120 onward for Autumn 2023.

If your post does not specifically relate to an FI chart then it doesn't belong here - Off topic posts will be moved

Thanks

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A new month, a new season and from the looks of things a new pattern change may well be on the way as we head from a very wet summer to perhaps signs of something dryer for the early part of Autumn.

First hint of a dryer pattern by 2nd September. Funny thing is it was 2nd September last year where we began a very wet autumnal pattern after the hot dry summer of 2022.

High pressure well and truly centered over us by the 5th.

IF this verifies this will be first genuine area of high pressure to influence our weather since mid June.

Deeper into FI the high shifts towards Scandinavia and we pull in a warm easterly from the continent. While this would make eastern areas cooler than the rest of the country the cooling effect from the sea breezes would be nowhere near as sharp as they were in May and first week of June.

We finish up with an area of low pressure from the Bay of Biscay trying to break down the warm and settled weather as we head towards mid September.

Temperatures on this GFS run getting close to mid 20s at times with low 20s quite widespread across the country especially if there are decent spells of sunshine.

Not a lot of rainfall over the first 10 days of September, very small amounts compared to what we've experienced all through July and various stages of August.

At the moment the models are looking good for things settling down with a warmer than average first half to September looking likely.

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Billcarson

Same, I would take a crappy first few weeks of Dec if it meant a better chance of a cold spell around Xmas. A cold snap end of Nov would be nice too though. I kind of hope any cold end of Nov will just be a snap if the cold happened to extent into eary/ first half of December I think that lessens the chance of a cold Xmas. Last yr being a perfect example. Even in Dec 81 it got milder during Xmas and 2010 milder from the 26th. ( not that I wouldn't say no to another Dec 81 or 2010)

joinme

Given our recent miserable, mild winters, where its the hope that kills you, I wouldn't be bargaining with the cold. Take the cold when it's on offer, every time.

Billcarson

https://www.boards.ie/discussion/comment/121388182#Comment_121388182

Very true indeed beggers can't be choosers when it comes to cold in this country.

.Donegal.

https://www.boards.ie/discussion/comment/121388138#Comment_121388138

I remember 2000 well. Me and the rest of the kids on the street were outside from dawn to dusk everyday during it. I think it lasted around 5/6 days? I bought a crap thermometer and put it outside on the sitting room window sill(very scientific) used to check it before bed. Around -11/12 if I remember correctly. Majority of the snow fell early in the first morning. Snow showers continued on and off but not to that extent. Was a deep fall.

[Deleted User]

I think too much emphasis is placed on drivers, if drivers were such a great predictor of future weather then long range forecasting wouldn't be as hopeless as it is. There's very little accuracy in predicting even broad trends for the coming months.

Billcarson

https://www.boards.ie/discussion/comment/121388209#Comment_121388209

Think it got down to -13c in Mayo during that spell, the coldest this century until 2010. Also the coldest at that point since the 80s I think.

sryanbruen

https://www.boards.ie/discussion/comment/121388342#Comment_121388342

Indeed.

25 Dec 2010 -17.5C (Mayo)

20 Dec 2010 -17.2C (Sligo)

03 Dec 2010 -16.4C (Kilkenny)

08 Jan 2010 -16.3C (Kilkenny)

29 Dec 2000 -14.0C (Mayo)

28 Dec 1995 -13.3C (Donegal)

10 Feb 1991 -13.0C (Kildare)

12 Jan 1982 -15.2C (Offaly)

12 Dec 1981 -12.9C (Meath)

02 Jan 1979 -18.8C (Kildare)

PokeHerKing

12z looking beautiful 👌

WolfeEire

GEM and GFS op runs are miles apart. The reality will be somewhere in between based on all output at this stage.

esposito

It’s annoying that the models can’t agree 7 days out! The fact that GFS and GEM are like chalk and cheese is ridiculous.

Anyway GFS as it always does, teasing us with amazing winter charts that 99% of the time never come to fruition 🙄

nacho libre

https://www.boards.ie/discussion/comment/121388209#Comment_121388209

Ah it was epic alright. Two days of near continuous heavy snow and it stuck like goodo, then it stayed on the ground for several days afterwards. Good times!

nacho libre

https://www.boards.ie/discussion/comment/121388486#Comment_121388486

I bet the ECM will follow the GEM, then we will get the inevitable GFS climb down

PokeHerKing

ECM still on board, 12z looks better than 0z. Still day 10 for anything really cold though

pauldry

Looking more and more like cold weather to end November. Both ECM and GFS have it on pub run. Oh the pub run.

nacho libre

https://www.boards.ie/discussion/comment/121389942#Comment_121389942

So the reverse psychology has worked. Hopefully now we will get a few settled days at least, before normal service likely resumed in December.

Dazler97

https://www.boards.ie/discussion/comment/121388981#Comment_121388981

Oh that's lovely 😍 👌 now let's hope all other models come on board with this 😀

Gonzo

The pub run is cold, the overall trend with the GFS ensembles is a cold spell to end November and start December, we ain't looking at much if any snow but certainly plenty of sub zero frosty nights and some wintry showers in places with brief coverings of graupel and sleety hail. Far more seasonal than the usual long fetch south-westerlies on a conveyer belt of muck. There are a few isolated runs which give a snowy scenario but most are cold with frost and wintry showers.

If the above verifies it's one of the more seasonal transitions from Autumn to Winter than what we are used to.

nacho libre

P 30, please, Bob.

Gonzo

https://www.boards.ie/discussion/comment/121390146#Comment_121390146

That's a beautiful chart and the one outlier that gives a 16cm snow reading for Meath, highly unlikely but it is on the table. However for now just like the ultra mild charts it can't be ignored as anything is possible over the next few weeks.

nacho libre

https://www.boards.ie/discussion/comment/121390151#Comment_121390151

I think we will go back to milder and unsettled weather early in December. I wouldnt be shocked to see a far more sober fi from the GFS in the morning.

The only thing is the very cold air in Scandinavia has built up earlier than usual in a El Nino. So if we can tap into that then such charts are certainly possible

Gonzo

https://www.boards.ie/discussion/comment/121390161#Comment_121390161

Yeah usually the GFS sobers up just in time for Winter, November always delivers the 'bank' charts especially over the past few years and every winter since 2019 has been absolute horrific from a snow bunny perspective.

However I've a feeling this winter may get closer to delivering a few days of white gold compared to recent winters but time will tell.

sryanbruen

Most recent GFS finally back down to earth with regards to amplification in the Atlantic, as expected. We get a shot of a northerly the coming weekend though far from a guarantee Ireland would feel the effects - for example, see the below. The ECM shows Ireland mostly in a milder Atlantic flow whilst the cold air advection goes to the east of us. The GFS has the colder push further westward near Ireland. This in practice means the ECM solution would give daytime temps more in the high single figures or touching low double digits whilst the GFS would be more mid to upper single figures. Both would bring the risk of frost by night provided skies are clear, winds look reasonably light in nature.

Then more differences happen following the weekend. The ECM goes for a more ridgey setup with the high pressure sticking about after toppling though does bring in an upper low temporarily by the 26th into the 27th which would bring the threat of outbreaks of rain especially to the southwest of the country.

The GFS is more unsettled with an Atlantic flow immediately returning. It has a brief ridge for 1st December but after that it turns very unsettled.

Will the 12z go back to fantasy land?

nacho libre

https://www.boards.ie/discussion/comment/121391222#Comment_121391222

I doubt it. Once they smell the coffee that's usually it. What I mean is the output this morning is far more realistic given there is no real background drivers to support amplification into Greenland. Maybe if the MJO goes to a more favourable state that might change. Is there any sign of that in the next few weeks?

pauldry

Itl all be back on the pub run tonight. When they go on the sauce everything goes blue!! When they wake up its green and orange again

sryanbruen

No Atlantic flow out to early December on the GFS 12z, very dry.

sryanbruen

https://www.boards.ie/discussion/comment/121388285#Comment_121388285

I think Catacol puts it perfectly on Netweather on the use of drivers (or as he mentions "teleconnections" which are the same thing).

I don't think the issue is the teleconnections themselves. They are understood. The issue is that these teleconnections are themselves a product of a forecast. So we build a forecast built on another forecast and consequently we get accuracy mayhem. Take the next pacific wave. When it comes there will be another opportunity for high lat blocking to take hold. I am 100% confident of that because the end product of the wave pattern promotes potential wave breaking over the north atlantic. BUT the timing of that wave could be up to 14 days either way, and the amplitude of that wave will affect the chances of the block emerging. And we are therefore not dealing in certainties.

Timing is therefore a big issue. And a bigger issue is that a forcing we describe as a teleconnection (just a fancy word for a cause tbh) is only a ticket to a higher probability. And a 95% probability scenario can still bust. Dec 2012 remains hurtful.

So - to bring this to a close. Chance of snow in the UK in lowland areas tomorrow I'd put at zero. Chance of snow in lowland areas of the NE or central England early next week perhaps increases to 10%? This on the back of lagged 7/8/1 impacts. The teleconnection (cause) is in play. But it still isn't a guarantee of anything. If folks relaxed a bit and took on board the nature of this game of chance we play when hunting snow it would get a lot less stressful.

They are no guarantee. There never is any guarantee. It's all about probability, that's what forecasting is primarily based on. Sometimes these teleconnections or drivers will allow a highly accurate forecast (in terms of general trends) well in advance and contingency planners can use them as a means of preparing in case of emergencies or saving lives. May sound a bit silly but it happens. Of course nobody's gonna give a hoot about my amateur posts but I do this for fun and a distraction from talking about the past all the time. The present is often boring after all 😉

Other times the teleconnections may dramatically change, not verify as expected or a spanner has been put in the works. July 2023 was an example of the first where we seen a collapse of all active MJO activity that helped drive the May/June drought period. July could have panned out very very differently. Winter 2018-19 was an example of the second case where for numerous months, a major SSW was well predicted which some will say was pure pot luck and fair enough, that's your own opinion. The seasonal modelling had a heavy emphasis on a -NAO signature for the winter of 2018-19 and it was theorised they were seeing a downwelling of a major SSW that would cause a very blocked second half to the winter. What we got instead was a displacement with blocking in a position that favoured the midwest United States and the SPV recovered a lot to the point that the opposite of a major SSW event happened through February/March 2019 in the form of a record-breaking strong SPV event which aided in the exceptional mild conditions we had. There's too many examples of the last case, how many times over the years have you heard the term "conflicting signals"?

Whilst on the talk of teleconnections, seen numerous mentions of the prospects of favourable MJO progression through the second half of December (not just Matt Hugo) for blocking to develop @nacho libre. Haven't really looked at it. The one question I have is what would the stratosphere say to it.

sryanbruen

One of the more interesting runs I've seen, the EC this evening tries to develop a Scandi with a very decent cold pool for the time of year to the east but gets put off by an Atlantic ridge which brings the return of northerly winds at the end of its run. Completely different evolution again however to anything the models have shown - at least in terms of the deterministic runs.

Its hemispheric profile looks excellent for stratospheric disruption too with blocking over the Urals and troughing over the Aleutians.

Just posting purely for fun.

PokeHerKing

12zs have definitely extended the garden path

nacho libre

GEM is similar to the ECM Control. This, if it happens, should ensure no conveyor belt of lows for a while. Also it would put pressure on the Polar vortex too.

pauldry

Apart from some frost and dry weather which is good proper Winter cold seems to be fading by the year. A day here and a day there.

Looks a lot drier away from the NW and even here much drier than recent. High Pressure taking up residence at or near us until early December.

Far off into the distance Xmas still looks mild. Bah!