0.6c above the 61 to 90 average

Bang on the 91 to 20 average

My prediction was way off, I didn't think it  would get so cool.

The resulting chilling of the ground tends to prevent solar insolation from offsetting the anomalously low minimums with as-anomalously high maximums. So you have a means of dropping the CET substantially that isn't dependent on cold airmasses. That's been evident in recent days, as the airmasses have been on the warmer side, but the nights have remained notably chilly, and the days have barely reached above average.

If I have the numbers right, I'll stay put in the middle of the table this month, perhaps in 12th. This year keeps teasing me with some very good results, only to tie my shoelaces every 2nd or 3rd month 😅

It's an unexpected win but finally my strategy of going too low had to pay off. 🙂

I get a figure of 14.09C when computing (max_min)/2 to 2 decimals

https://hadleyserver.metoffice.gov.uk/hadcet/cet_info_mean.html 

The result is an interesting leader board with a huge battle going on mid table - nearly half of those playing are within half a degree of each other. A special mention has to go to Stormchaser and Domma who have been neck and neck since June exchanging places in the table within fractions of a degree of each other and with just 0.02 separating them this month there's all to play for in October. There's been a change to the top 3 as well with Dickieboy68 continuing their strong performance this season and now in 3rd place. After forgetting to put my prediction on the opening page of the thread I incur a missed prediction penalty and as a result drop to 6th.

Without further ado here is the September Leader board:

The result is an interesting leader board with a huge battle going on mid table - nearly half of those playing are within half a degree of each other. A special mention has to go to Stormchaser and Domma who have been neck and neck since June exchanging places in the table within fractions of a degree of each other and with just 0.02 separating them this month there's all to play for in October. There's been a change to the top 3 as well with Dickieboy68 continuing their strong performance this season and now in 3rd place. After forgetting to put my prediction on the opening page of the thread I incur a missed prediction penalty and as a result drop to 6th.

Without further ado here is the September Leader board:

I'm having a shockingly bad year and this coming month probably won't fair much better. Can't seem to judge it well, at all!😂😂

Think you're being unduly harsh on yourself there, Dave

Yes, that does seem harsh as you do all the actual work behind the scenes... perhaps it could be a provisional/yellow card/sin bin type of thing that only gets included if it becomes critical ... ??? 

Well play all - see you at the end of October!

I appreciate the thought but I can't uphold the rules if I break them myself and get away with it - too much of that going on in the world already! 🤣

I'll have to settle for a stunning comeback instead! 

Which is to say, we're all doing better than if we just assumed 'as before, so after'.

For anyone wondering, using the average of all years in the (very long!) CET record, you'd be on a whopping 16.65°C!

Has every month this year been milder than the 91-20 average?

Almost. The opening month was actually pretty chilly by that standard, while September was just a smidge below.

March-August was an exceptional run of anomalous warmth, in fact unprecedented in the CET record.

Even when using a moving baseline to account for the climate trend, there are few historical instances of 6 months comparably far above, but I can find a few more impressive runs.

Most of all, eight months June 1781 to January 1782, where all but one were at least 1°C above and the exception 0.8°C above.

1959 had a run of 8 at least 1°C above with the exception 0.7°C above.

1933 saw run of 7 at least 1°C above, the exception 0.8°C above.

There's also a 5-month run of 2-3°C above spanning November 1821 to March 1822, which must have felt utterly bananas at the time.

Of course, 2025's impressiveness gets a boost from the fact that the absolute level of warmth is greater and hence less 'classically British' in nature. The monthly departures from 1991-2020:

2025

-1.25°C

0.34°C

1.18°C

1.89°C

1.30°C

2.38°C

1.61°C

1.12°C

-0.08°C

Interesting, James - and thanks for the data

I'd been wondering, after your initial post, what the impact would have been if someone had gone 1c above the 91-20 average each month.

My bag-of-a-fag-packet calculation suggests they'd be sitting on an aggregate of 7.15c, so out of the running anyway.

The whole scoreboard is a fair bit more compact than I remember it being in previous years

I get 7.88°C, 29% of which comes from a 2.26°C error in January. So that person would be 20th in the table.

That long run of persistent warmth seems to have discouraged below average estimates more than ever this year.

Even when longer-range guidance suggests a colder pattern may feature, it's hard to gain enough confidence in below average temperatures being as high-magnitude and/or prolonged enough to prevent the monthly mean CET being at least near-average, if not above.

This October is a good example of that. All the longer-term signal for a -NAO pattern did was restrain my estimate to be closer to average... how boring of me 😅