May 2024 C.E.T. and EWP forecast contests

[Frigid]

I can already see this month becoming exceptionally mild.. unless we see a cooler second half similar to April.

[Metwatch]

For anyone curious on May 1833, this post might help. Reason being is this May does have the potential to get close to 1833 but depends on what happens in the second half. The CET value of May 1833 also comes from London, rather than the 3 places used today, hence it being higher than if it was used with stations further north like today.

Edited May 2 by Metwatch

[Scorcher]

 Metwatch As I mentioned the other day in another thread, I think the May 1833 record is one that could be absolutely smashed in today's climate- a bit like how April 2007 smashed the previous record by some distance.

It's bizarre to me that it's such an anomaly as a much higher CET is theoretically possible in May.

I actually think the fact we haven't had another 14C+ May is one of the oddest statistical quirks of the British climate.

Edited May 2 by Scorcher

[Weather-history]

 Scorcher

May and June CET records for some reason seem to be more resilient than the others. The only top 5 of recent times for either month was June 2023.  The next one after that is May 1848

Only 3 of the top 10 Mays have occurred since 1900 

 

Edited May 3 by Weather-history

[Scorcher]

 Weather-history Yes I find it quite puzzling to be honest as May and June are the two months that could go much higher than they have.

I know it will never be the norm to expect 14C+ Mays due to SSTs and seasonal lag but I find it very odd that there hasn't been one month in nearly 200 years that has managed it 

I imagine part of the reason is night time minima at this time of year. A high pressure dominated May can produce high maxima but nights generally drop into single figures if the high is directly over the UK.

2018 was a prime example here- the average maximum at Rostherne was 19.4C but minima were often in single figures and a fair few nights dropped below 5C.

[LetItSnow!]

 Scorcher I don't know if you saw but in the thread about May 1833 and the polar (no pun intended) opposite spring of 1837, but the C.E.T. station was actually solely being recorded in London at that time. Now of course London was far less of a UHI producer back then, but the locale suggests that while it's still an exceptional month, if it had data from further north like now, it may have indeed been a tad cooler than 15.1C. Maybe at least. May 1992 apparently had a warmer mean than 15.1C in London but that's of course by the time London was built up. Interesting nonetheless.

[Scorcher]

 LetItSnow! Yes I had no idea until yesterday that 1833 wasn't as impressive as I thought. It's not really a level playing field if it's being compared to modern Mays with the data being collected across the country.

[Relativistic]

 Scorcher I simply cannot believe that when the series was created and in the recent revisions since that adjustment work wasn't carried out to smooth out its inconsistencies. What use is it otherwise? The Met Office are a scientific organisation and surely would never let something so shoddy pass.

Edit: @Derecho has addressed this in the other other thread.

Edited May 3 by Relativistic

[Summer Sun]

13.5 to the 2nd

2.3c above the 61 to 90 average

2.9c above the 81 to 10 average

[B87]

 Scorcher Here are the 15c+ May mean temps in London in recent years.

1989: 15.5c

1992: 15.6c

2008: 15.2c 

2017: 15.1c

2018: 15.3c

2020: 15.1c

2022: 15.2c

It isn't such an anomaly when you only use one station to record the CET mean.

[Derecho]

 B87  The raw temperature was not used to calculate the CET but the anomaly from the station average. Here is a more detailed explanation from another thread I posted on:

 

To follow my earlier post, the temperature anomaly in London will have equated to 3.9C above the 1961-90 average there, the raw value would not have been 15.1C that appears in the CET series.

The CET value would have been 11.2C + 3.9C London anomaly = 15.1C. If the raw temperature for London was used you'd see a long sustained upwards spike in CET before it became 3 stations, outside of winter and especially for summer months as SE England is warmer.

In order to beat the 1833 record, you'd need an average temperature anomaly of +3.9C at Rothamstad, Pershore College and Stonyhurst, rather then just a +3.9C temperature anomaly over the London area.

That would be difficult even in todays climate, every once in a while you get a month of truly exceptional weather.

Edited May 3 by Derecho

[B87]

 Derecho It was taken from London alone in 1833 though. 

May average in London now is 13.8c, so you are saying we would need to have a 17.7c mean in May these days for it to equate to 1833?

Edited May 3 by B87

[Metwatch]

 Derecho My question to that is what other stations were used to help calculate the CET back then; would there have been any others used further north such as in the Midlands? The +3.9C anomaly, i'm not quite seeing where that comes from and why the 1961-90 average is used (May 61-90 is 11.1C I think). Perhaps I missed where it was mentioned in that journal about how the CET was calculated back then?

Edited May 3 by Metwatch

[Derecho]

 B87  It's not the raw temperature used to calculate the CET mean, it's the anomaly from the average at the London station that is applied to the CET mean.

It doesn't matter how much warmer London is compared to the CET mean when you are basing the CET mean off station anomalies unless you see regional variations in temperature anomalies associated with persistent weather patterns.

[Derecho]

 Metwatch I think the challenge with such long series of temperature is the need for overlapping observations to homogenise the data. London is a lot more handy in this regard as there were many observers going back to the 18th century.

Armagh has daily temperatures going back to 1796 (I think!) and Edinburgh has monthly means going back to 1764 I think but I'm not sure there are many other stations in the UK that have overlapping stations going back that far (Radcliffe Observatory in Oxford is another).

Maybe a UK series based on Edinburgh, Armagh and London would be more handy though only London and Armagh have daily data going that far back for the duration.

Edited May 3 by Derecho

[Derecho]

CET returns from the 00z EC control, as expected it is a warm outlook. The control is definitely on the warm side from the 11th to 14th but I wouldn't call it an outlier.

The result if it verified would be an impressive CET of 14.5C up to the 15th but as recent model output has shown, this output should be taken with a pinch of salt. Today for example looks likely to return a pretty average CET value.

[Addicks Fan 1981]

 Derecho flipping Henry is all I can say to the warmth.   

[Roger J Smith]

1833 got to its highest position of 15.6 by 24th and gradually fell back to 15.1. 1833 also set two daily records near 20C at mid-month. Apart from those, no really exceptional daily means. 

I take it from previous discussion actual average at recording site was higher than 15.1, it was some value 3.9 above 1961-90 average for same location near London? So probably closer to 16? (3.9 over possibly 12.1)

It's all a bit confusing but I see the logic of adjusting that way. If CET was all one London (west) station now, it would

(a) need a larger urban heat island correction of 1.0 to 1.5 and

(b) in climate terms would likely be 1.0 to 1.5 higher, so you would need to take 2-3 off London averages nowadays to find a realistic analogue to CET.  

 

[WYorksWeather]

 Roger J Smith And of course the need to also disentangle the UHI effect under different conditions - you'd probably have to use a different corrective factor by season and of course day vs. night.

[Summer Sun]

12.3 to the 3rd

1.2c above the 61 to 90 average

1.7c above the 81 to 10 average

[Metwatch]

For this spring to become the warmest on record for the CET zone (current warmest is spring 2017 with a CET of 10.27C / 10.3C ), May's CET will need to come out at 13.1 / 13.2C.

Would be quite undeserving for a spring like this one but it is possible if this May is fairly warm throughout. Spring 2017 wasn't overly dry or sunny either compared to 2011 at least, (second warmest spring) so to an extent that may have also been undeserving at the time. I don't remember what Spring 2017 was like, but looking at stats April was the driest and sunniest month, with March and May wetter and duller.

Edited May 4 by Metwatch

[damianslaw]

Could be an odd spring, a very wet dull but one of warmest on record. Lack of clear skies preventing cold minima, and all the cloud and rain associated with very mild maritime air aided by exceptional warm SSTs to our SW. If it does end up mildest ever, it won't be remembered fondly by most. 

[Don]

 damianslaw Could it be a similar story for the coming summer i.e. wet and dull but also very warm and humid?!  If so it most certainly won't be fondly remembered by me!  That said, it could also be a hot and dry summer with relatively low humidity but the concern is the warm SST's to our south west will work against us for that?

[LetItSnow!]

 damianslaw A very typical set-up for the 21st century. Not the topic for it here but you have to wonder if the extra moisture in the warmer air is disproportionately affecting the nights more than the days during the warmer half of the year.

39 minutes ago, damianslaw said:

very wet dull but one of warmest on record

 

[reef]

 damianslaw The perception might be that its from warm minima due to cloud but its actually not. The anomaly is very similar for both (approx. +2.2C and +2.0C vs 1961-90). It has just been consistently mild/warm by day and night but with no real standout warm maxima.

Edited May 5 by reef