Mild September = A Mild Winter?

[North-Easterly Blast]

I think that even though it is a long way off, the earliest background signals for winter 2024-25 are already bad news from a cold perspective for the UK, with a westerly QBO, and being close to solar maximum, and the likelihood of a La Nina.  The only thing that it not known at this stage is what September 2024 will be like - if anomalous September warmth will again kill off chances of cold in winter 2024-25.

[North-Easterly Blast]

 Bristawl Si After such an exceptionally warm September last year, considering how strong the fact of the UK's weather patterns are that anomalous warmth in September does not favour cold conditions during the following winter, as over the centuries, colder winter weather has been very infrequently seen after a warm September (although it is only clear that warm Septembers have an effect on the following winter, and there is no evidence to suggest that cooler or average Septembers have any bearing on the following winter), I think that winter 2023-24 was already "dead in the water" before it even started.  The same was true for other winters in 2021-22 and 2016-17, and further back in 2006-07 and 1999-2000; these winters were already dead in the water before they even started after very warm Septembers.  2023-24 simply joins a list of winters that were ruined by warm September forcing.

It clearly appears to be the most predictable aspect of the British Weather, that anomalous warmth in September means that almost if not all the following winter will be mild.

Edited February 12 by North-Easterly Blast

[Methuselah]

 North-Easterly Blast

Well, I'm yet to see any evidence (compelling or otherwise) that warm Septembers cause mild winters. . . If it were that simple, the UK Met. Office would be on it like a flash? 

[Bristawl Si]

 Methuselah agreed. Sept 2010 was warm and dry here imby. Late Nov into December 2010 was freezing.

[North-Easterly Blast]

 Bristawl Si September 2010 was not particularly warm; it had a CET of 13.8, which is just above the 1961-90 average but a little below 1991-2020, so I would not be testing the warm September = mild winter theory after a September CET of that level.  

For anyone looking for comparison of what a high September CET is, the 1991-2020 average is 14.2, and the 1961-90 average is 13.6.

I think that a September could be considered warm if it has a CET of 15*C or above, although on the older averages a September CET of 14.5 could be about the breadline.

I was meaning to say that it appears to be still possible to have a September CET that is slightly above average (1978, 2009 CET 14.2, 1981, 1985 CETs 14.5 / 14.6), and get a good winter for cold after it, but it appears that warm Septembers in terms of a high CET are bad news from a cold perspective for the following winter.

Edited February 12 by North-Easterly Blast

[Bristawl Si]

 North-Easterly Blast Admittedly i looked at day time temps for Sept 10 - ranged here from 22c to 15c. 1st half esp was warm during day.

[Derecho]

4 hours ago, Methuselah said:

Well, I'm yet to see any evidence (compelling or otherwise) that warm Septembers cause mild winters

Yup if a warm September causes a mild winter, then why not a warm October or mild November?

Edited February 12 by Derecho

[North-Easterly Blast]

 Derecho I do not think that it is clear that there is any trend between October or November as to the sort of winter that follows, or it is certainly far less clear cut than the warm September = mild winter theory.

[Weather-history]

 North-Easterly Blast

Why would this be?

You call it a theory. Did Newton when he gave his theory of gravity did he just  left it at that? No, he explained it

When Einstein gave his theory of relativity did he just left at that? No he explained it.

So I want an explanation. Why would the weather of a specific 30 day period in the Earth's orbit have an effect on the weather of a specific 90 day period in the Earth's orbit, where there is  61 days between the two periods?

  And why only a specific type of weather? In this case, warmth. 

Does it hold true, on other parts of the planet?  Does a warm September in New England mean a warm winter for that part of the world as well? 

Edited February 12 by Weather-history

[North-Easterly Blast]

 Weather-history Well after previous very warm Septembers (CET 15.5 and above) I think that all the following winters were mild.  Now looking at Septembers with CETs over 15*C the only times that I can think of where the warm September = mild winter correlation did not work too well, are Sep 1958 (15.1) that did go on to produce a cold January in between average conditions in the rest of the winter, and Sep 1961 had a CET of 15.2 that did go on to produce a significant cold spell in December which lasted into early January, and there was again another significant cold spell in late February and through most of March, though it did get milder in between these two cold spells.  I can also think of Sep 1929 (15.3 CET) that did go on to produce a cold February though the winter was largely mild before that.  Other than that, I can think of "not a lot" from a cold perspective in any previous winter following any September above 15*C CET.

Records show a fairly equal mix of colder and milder winters following a September that is cool or average CETwise, but the records certainly show that it has always been very rare to get colder winter weather after an anomalously high September CET.  I think that the further above average the September CET is, the worse it bodes for cold conditions in the following winter, and other than the above examples, I think that the warm September = mild winter correlation appears to have almost always previously worked, barring those few exceptions above.

Edited February 12 by North-Easterly Blast

[Mike Poole]

6 minutes ago, North-Easterly Blast said:

the records certainly show that it has always been very rare to get colder winter weather after an anomalously high September CET.

We had this discussion in the run up to winter.  The problem is, these days, it is very rare to get colder winter weather after any September (cold, average, warm, the lot).  And with climate change, warmer Septembers than historic averages are more common so it is possible to perceive a link that is not there.  Correlation is possible, therefore, but it doesn’t imply causation.  There is no logical reason I can see why a warm September in the UK of all places should affect weather patterns three months later.  (There are other places in the world where Autumn weather may affect the coming winter because it affects the developing polar vortex - the UK is not one of them!)

It may just be one of those statistical anomalies (like the 13th June used to be), but it is a theory that is rolled out every year.  Problem is, after this year, its nose will grow a few inches!  

[North-Easterly Blast]

 Mike Poole And in recent times in as much of a fashion as this year, the warm September = mild winter correlation also well and truly worked after Septembers 2021, 2016, 2006 and 1999.  On top of that, winter 2005-06, given the pattern that set up that winter, and the fact that the really cold air never quite made it to the UK, could have been an outcome that was contributed to by a fairly warm September (15.2 in 2005).

Edited February 12 by North-Easterly Blast

[Methuselah]

 North-Easterly Blast But it's not even a theory, it's like tossing a coin ten times and being amazed when you don't get five heads and five tails. . . 

[Mapantz]

The warm September guff should not be used in context to the  word "theory"

It's embarrassing to keep seeing it used in that way.

[Weather-history]

 North-Easterly Blast

That's not an explanation. That's a bunch of stats. 

 

[Badgers01]

On 10/02/2024 at 13:49, North-Easterly Blast said:

there is certainly fear that a winter like 2020-21 or 2017-18 may be the modern version of 2009-10, December

Just don’t engage - an interesting thread has been derailed by this nonsense theory or whatever you may call it ! 

[Met4Cast]

5 hours ago, North-Easterly Blast said:

I do not think that it is clear that there is any trend between October or November as to the sort of winter that follows, or it is certainly far less clear cut than the warm September = mild winter theory.

It’s not “clear cut” that a warm September = a mild winter either looking at the data shared in here by others. 

I think there’s some conformational bias going on here, in a warming world each individual month is more likely to be mild & as such, a mild September may well be followed by a mild winter because mild winters are far more likely these days. 

It doesn’t mean there’s a link and the evidence isn’t strong enough to show that there is. 

What are the mechanisms? Why does a warm September = mild winter? What drives that? What are the feedback loops that cause it? You have to demonstrate & show a positive feedback loop which influences weather patterns, otherwise it’s not helpful, useful or demonstrable. 

Edit: Just read the rest of the thread, I see @Mike Poolemade the same point re: climate change. 

Edited February 12 by Met4Cast

[Relativistic]

Oh for goodness' sake, not this again

[North-Easterly Blast]

 Met4Cast The warm September = mild winter relationship is a bit like how many years ago the UK Met used to use SST anomalies in May to predict the following winter's NAO.  If SST anomalies in May showed a tripole of warm / cold / warm anomalies in the north Atlantic during May then the UK Met used to predict a negative NAO in the following winter.  I do not know why May was chosen, but there must have been some correlation that SST anomaly patterns in May are more likely to repeat themselves in the following winter.  

Going back to the warm September / mild winter relationship - for a high September CET, it would normally be the result of high pressure centered over Central Europe and low pressure areas stalling to the west of the UK - it must be that when this pattern occurs in September that northern blocking is unlikely to establish itself in the following winter, and low pressure areas stalling out west are more likely to be followed by low pressure areas tracking SW-NE in the following winter.  The warm September = mild winter correlation looks like one of the things that are a bit like the May SST anomaly pattern being more likely to repeat itself in the following winter.

[Met4Cast]

 North-Easterly Blast

Worth noting that the May SST link with the following winter was largely debunked & is no longer used by the Met Office as an NAO predictor! 

With that though you could see the thinking, i.e SST’s do have impact on the NAO to some extent. 

Is the opposite true? Do cold Septembers correlate to cold winters? 

Edited February 12 by Met4Cast

[North-Easterly Blast]

 Met4Cast I am not sure that it is clear that there is any link between a cool September CET and the sort of winter that follows, whereas if the September CET is close to average, there does not appear to be any trend in the sort of winter that follows.  It is really clear that only warm Septembers have an effect on the following winter, in that a high September CET is nearly always followed by mild winter, and it is very rare to get much in the way of cold weather in a winter that follows a high September CET.

[Weather Enthusiast91]

September is still a long way off from winter, and anything can happen during that time.

Milder than average winters are the norm these days anyway, regardless on how September panned out. 

[danm]

No. End thread. 

[Methuselah]

 Weather Enthusiast91 So are mild Septembers: we are, after all, in a run of successive warm years, globally, and that's got to be more to-the-point than a thirty-day stretch that we humans have chosen to call September? 

[Gray-Wolf]

 Methuselah Well we had Ducks walking on the Canal at the end of November so that was Winter 'binned then! (according to the old sayings)....."Ice in November to carry a Duck....the rest of the winter will be mild & muck...."

I'm now waiting for my tree lore to see how Summer goes.....Öak before Ash....in for a splash.....Ash before Oak....in for a soak....

 

(Ahd 'YES' take with a large pinch of salt!!!)