This thread is for all comments, discussion and analysis of temperatures in the UK during May, with particular emphasis on the Central England Temperature (CET), for the simple reason that it is the longest running temperature series in the world with over 360 years of data. But you can comment on any interesting temperature statistics or data from across the UK, including your own back yard.

April has been a mixed month with a mix of cold and warm weather. Overall it will be above average due to the very warm Easter period.

For those taking part in the competition all CET predictions for May should be sent directly to me via the forum private message system. Do not post them directly into the thread.

The deadline for predictions this month is 2359 on Wednesday evening (1 May). 

Now on to some data for May:

Historic CET summary for May

1971-2000 11.3C (30 years)

1981-2010 11.7C (30 years)

1999-2018 12.1C (last 20 years)

The last two Mays have been very warm with above 13C CET returns. Those were the first years the May CET was above 13C since 2008. We had a number of cool Mays in 2010, 2013 and 2015 with below 11C returns.

Here is a chart of the May CET for all years since 1961:

Direct link to larger version of the chart

Latest model output 850hPa temperatures - 12z 28 April

GFS (12z) - generally close to average except for the Bank Holiday period which is cold

http://www.wetterzentrale.de/de/show_diagrams.php?geoid=49069&model=gfs&var=2&run=12&lid=ENS&bw=

GEM (00z) - very different and with more scatter than the GFS. No sign of the colder Bank Holiday and turns quite warm after that 

http://www.wetterzentrale.de/de/show_diagrams.php?geoid=49069&model=gem&var=2&run=00&lid=ENS&bw=

Multi Op (00z) - fairly good agreement except for GEM which goes off on one with its mild solution. GFS 0z was also milder than the other models

http://www.wetterzentrale.de/de/show_diagrams.php?model=multi&var=2&geoid=49069&lid=OP&bw=

The ECM ENS T2m temperatures for De Bilt show the cold bank holiday but remember this is for Holland and we are right on the periphery of a cold plunge into central and eastern Europe at the end of this week which is more likely to show up in De Bilt. Longer term there is a lot of scatter with the option of something very warm but also with a number of runs staying cool or close to average.  

http://cdn.knmi.nl/knmi/map/page/weer/waarschuwingen_verwachtingen/ensemble/detail/ensemble-verwachtingen-detail10.png

Met Office contingency planners outlook 

Not yet published - probably out tomorrow.

Temperature analogues

Last month's analogue signal was mixed but with the probability of a warmer than average month being greater than a colder than average month. In the end the month was very mixed but finished above average.

We are still tracking the CET for 2017 very closely this year. All four months have been very similar so far. That year had a warm May.

Looking at other years since 1950 where the CET for Feb to April is a good match for this year we have 2014, 2002, 1997, 1961.

1961, 1997 and 2002 saw a CET around average in May. 2014 was a bit warmer at 12.2C.

Looking at years with a March and April CET similar to this year we can also add 2005, 2003, 2002, 1999, 1992, 1959. The first three of these are close to or slightly above average. 1999, 1992 and 1959 are warmer.

So no signs of anything significantly below average in May from the analogues. The main cluster is close to or just above average (which also contains most of the best matches). A few years are quite warm. 

The analogues therefore point to something between about 11.6C and 12.1C as being the most likely scenario with a low probability of a warmer month closer to 13C.

First look at May temperature tracker 

Huge uncertainty in the output at the moment. So very low confidence on the current trends. The bank holiday weekend could be very warm or it could be quite cold. Latest output is going for the colder option but that is by no means certain. Even so generally the output suggests the first 12 days of May could be quite warm despite the possibility of a few colder days.

Contingency planners forecast from the Met Office has now been released.

Shows a greater probability of warmer than average conditions in May and for the period from May to July. But remember this is only a probability based output. You can see from the individual data points (in pink) that most are clustered around the long run average temperature. There are a small number of much warmer options but no really cold options. So that is why the overall position shows as slightly above average. Overall I would say this does hint at a close to average month. So far this year every month since January has been significantly above average. I think May might break that trend with something closer to average but probably still a little above.

https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/business/public-sector/civil-contingency/forecast-temp-mjj-v1.pdf

I just take no notice of the models at the end of the month because they always lead me down the wrong path!  Having said that, my gut feelings haven’t served me well this year either!  

My mean of 10 using a 6-  year average is going to be  12.02c.. 

 

The deadline for predictions this month is 2359 on Wednesday evening (1 May).

Glad I thought to check this, it's normally the 2nd of the month!

 

Glad I thought to check this, it's normally the 2nd of the month!

it depends when I post up the thread. In theory it should be the last day of the month but I usually don't get the thread up in time for this. I like to give at least 3 days notice for predictions to be made. I was a bit earlier posting the thread this month than I have been for a while.

 

Glad I thought to check this, it's normally the 2nd of the month!

Simon, I'm pretty sure you said at the start of the year that every month's prediction deadline would be at the end of the 2nd. As such, I've put a reminder in my calendar to submit my prediction then. I only looked at the thread by chance this evening, if I hadn't done then I would have been too late. That may be the case for others. I'll see if I can find the post where you said that.

 

Simon, I'm pretty sure you said at the start of the year that every month's prediction deadline would be at the end of the 2nd. As such, I've put a reminder in my calendar to submit my prediction then. I only looked at the thread by chance this evening, if I hadn't done then I would have been too late. That may be the case for others. I'll see if I can find the post where you said that.

It was in the Jan 2019 CET comp:

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How do the competitions work?

 Each month a new thread is opened a few days in advance of the start of a new month. Your challenge is to predict the mean Central England Temperature (CET) for the following month. The CET is the longest running temperature series and goes back to the mid 1600's. Each month I post some statistics about the CET for that month in recent years as well as a summary of some of the latest model output and long range forecasts to provide some context to assist you in making your prediction.

 Predictions can be made either to one or two decimals (the actual data is published to two decimals). The closest person or persons to the final figure at the end of the month are declared the winner for that month. There are no prizes. This competition is just a bit of fun and the chance to amaze your fellow posters with your skill and foresight in predicting the weather (or you can just make a random guess!).

 We use the Hadley data for the purposes of this competition which is maintained by the Met Office. Provisional figures are published daily with a final adjusted number usually issued on the first day of the following month.

 In addition to the monthly competition there is an annual competition which runs throughout the year. The annual competition keeps a running total of the cumulative prediction errors from each month for each person. Absolute differences are used so it makes no difference if you overpredict or underpredict the CET in any given month. At the end of the year the person with the lowest cumulative prediction error after totalling each of the 12 months is declared the winner for the year. This is always a hard fought contest and requires a consistency of good predictions in order to win.

 Summary of important points

  -Predictions can be made up to 23:59 on the 2nd day of the month to which the prediction relates. No entries will generally be accepted after this time unless I am late in opening up the thread.

 -All predictions should be made by private message to me. 

 - Once you have sent your prediction you are only permitted to change it once prior to the deadline. Any subsequent amendments will be ignored. 

 - You may make a prediction to either one or two decimals. You can predict the same figure as someone else.

 - Where two members have the same cumulative prediction error for the year at the end of any month, the order of ranking in the competition table will be determined by which person has had the closest prediction to the actual CET in any month. If there is a still a tie I then look to the second closest prediction for each person and so on until the tie is broken. If the tie cannot be broken (very unlikely by December but can happen in the first couple of months of the year) then each person impacted is awarded the same position in the table.

 Missed predictions

 If a person participating in the annual CET competition does not make a prediction in any one month (including January) their prediction error for that month will be calculated as follows:

 - the upper quartile (75th percentile) of the prediction errors of all the people in the annual competition who did make a prediction for that month will be calculated at the end of the month;

 The result of the above calculation will be used as the CET prediction error for any person who misses a prediction in a particular month subject to one further point:

 - If, for any person, their average monthly prediction error for all the previous months in the year to date is higher than the 75th percentile of errors (for those that did make a prediction) in the month the person in question made no prediction, then the average prediction error will be substituted instead of the 75th percentile figure. This override is only likely to apply to those people towards the foot of the table who have very made very large errors in previous months.

 -One final important point. If you want to be included in the year long competition you may not miss more than two predictions during a calendar year. If a third prediction is missed that person will be eliminated from the annual competition (otherwise it would mean 25% or more of the annual error being calculated on non-existent predictions which would reduce the credibility of the competition too much). However, that person can continue to make predictions for the purpose of the monthly competition.

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As an aside

Now that we do our posting via email rather than into a thread, shouldn't we just make our estimates by 23:59 on the last day of the previous month so that we don't have the dubious benefit of a couple of days actuals and updated models

Thanks Lanky! The drop-down to change the view from only the last two weeks' threads doesn't work for me (on Chrome / Windows 10) so I'm glad you found it somehow...

Thanks Lanky! The drop-down to change the view from only the last two weeks' threads doesn't work for me (on Chrome / Windows 10) so I'm glad you found it somehow...

I discovered it by accident

You have to set the time period to "All" then go into the "jump to another thread" and choose (say) Photography then select "jump" again and jump back to Weather and then it works - for threads that Brian hasn't restricted to just a couple of weeks by admin deletions

I'm also late - away at the moment but thought I would be OK till the 2nd - hopefully Simon will be in a generous mood!

No update from met Office since 27th April

Metcheck         10.80c.       Anomaly      -0.61c.

Netweather      11.76c.       Anomaly      0.46c.

Mean of my 10 watched stations    11.48c.   Anomaly    -o.54c.                

 

Simon, I'm pretty sure you said at the start of the year that every month's prediction deadline would be at the end of the 2nd. As such, I've put a reminder in my calendar to submit my prediction then. I only looked at the thread by chance this evening, if I hadn't done then I would have been too late. That may be the case for others. I'll see if I can find the post where you said that.

Sorry about that. You are correct. The 2nd it is.

I have been fairly generous with allowing late entries over the past couple of years (I only crack down when Saint gives me a hard time about it ). So nobody need panic.

No Met Office Update

Metcheck             10.30c.      Anomaly     -1.11c.

Netweather          11.12c.      Anomaly     -0.19c

Mean of my watched 10 stations      10.48c   Difference    -1.54c.   

Metcheck                9.24c.     Anomaly    -2.17c.

Netweather            10.11c.    Anomaly    -1.2c.

Mean of my 10 watched stations  9.64c.  Difference  -2.38c.     

Metcheck                9.24c.     Anomaly    -2.17c.

Netweather            10.11c.    Anomaly    -1.2c.

Mean of my 10 watched stations  9.64c.  Difference  -2.38c.     

... and I see that there's still been no update from Hadley since 28 April (which I can tell from the fact that this website still only gives the provisional value for up to 27 April).

As Gavin P. said in his forecast video for this month, it is very unusual for all of the UK data for any given month to have been released before everything from Hadley is up to date, so there is clearly some sort of delay within Hadley itself (which forms only a small part of the Met Office) rather than within the Met Office as a whole.

Latest update on the May CET. Very cold over the next few days. The mean will be down in the mid 8's. 

Temperatures don't get back above average until Monday 13th. It is likely to be at least the 21st before we get up to the 1981-2010 mean. The current forecast temperatures for the next couple of nights that are baked into these numbers do not I think fully take into account how cold it will be tonight and again tomorrow night. So it does look like a very chilly first half of May.

The first May Day Bank Holiday was in 1978 on the 1st of May

Here are the CETs for the May Day Bank Holidays

2nd May 1983: 7.4
4th May 1987: 6.9
6th May 1991: 7.2
6th May 1996: 7.4
3rd May 2010: 6.7 

Current estimate of the CET for the bank holiday Monday is 7.3C. So not the coldest but not far off. It will depend on how cold it is tomorrow night. Could well be nearer 7C in which case it could be the third coldest in the list above.

The CET for tomorrow (Sunday) is expected to be no higher than 6.5C and I suspect it will in fact be nearer 6C as I expect it to be very cold tonight.

So it will certainly be one of the coldest May Day bank holidays on record.