December 2024 C.E.T. and EWP forecast contests -- start of 2024-25 contest year -- all welcome

[Roger J Smith]

On behalf of J10 and myself, welcome to another new competition year with the winter season of 2024-25 fast approaching. Thanks also to Summer Sun and the PIT who contribute daily updates most of the time. ... and of course thanks to you, the loyal contest entrants and supporters. ... There has been a temperature (CET) forecast contest running on Net-weather since winter of 2005-2006, and the scoring system devised by J10 was introduced just a few years into that period. The EWP contest is newer, and has been going for seven years now and began in Dec 2017 for the 2017-18 contest year.

The contests include the CET forecast and the (optional) EWP forecast, with some guidance provided in two sections below ... 

 

CET averages and extremes for December

--- all CET values 1981 to 2023 are in the table --- they are in highlighted type to make them easier to find

--- --- --- bold type for warmest, italic for middle and underlined for the coldest thirds of these 43 most recent years. 

--- --- --- due to ties for 4.7 C there are 15 in total among the lower third and 14 for the  other two.

... all values in the CET contest have been converted to v2.1, including the averages for various intervals. ... v2.1 for Dec is often 0.1 above v2.0.

 

13.1 ... warmest daily mean, 19th 2015

12.9 ... 2nd warmest daily mean, 31st 2021

12.7 ... previous (to 2015) warmest daily mean, 12th 1994

 9.7 ... warmest December 2015

 8.1 ... second warmest December 1934

 7.9 ... third warmest December 1974

 7.7 ... fourth warmest December 1852

 7.6 ... fifth warmest December 1733

 7.5 ... sixth warmest December 1710

 7.4 ... tied seventh warmest Decembers 1828, 1843, 1988

 7.3 ... tied tenth warmest Decembers 1857, 1898

 7.2 ... tied 12th warmest 1842, 1868, 1900

 7.1 ... 15th warmest 2023

__ values, ranks and ties outside modern interval no longer noted, 7.0 has no instances in v2.1 CET __

 6.9 ... 2018

 6.5 ... 2006

 6.4 ... 2013, 2021

 6.3 ... 1994

 6.2 ... 1985

 6.1 ... 1986

 6.0 ... 2011, 2016 (in CET legacy there never was a 5.9 recorded, 2011 and 2016 were 5.9 in v2.0, with 1977 so there were three, now only 1977 is at 5.9)

 5.8 ... 2019

 5.7 ... 1997

 5.6 ... 2002

 5.5 ... 1983, 1987

 5.4 ... 1993, 1998, 2000, 2004

 5.2 ... 2014

 5.1 ... 1984

 5.1 ... average for 2001-23 

 5.0 ... average for 1994-2023, also 2007, 2020

 4.9 ... average for 1991-2020 and also 1971-2000

 4.8 ...1999, 2012, 2017

 4.7 ... 1989, 2003

 4.6 ... average for 1901-2000 and

 4.5 ... average for 1961-90, 1981-2010 ... and 1991

 4.4 ... 2005

 4.2 ... 1982, 1990

 4.1 ... average for 1659-2023 (all 365 years)

 4.0 ... average for 1801-1900

 3.9 ... average for 1701-1800

 3.6 ... 2008

 3.5 ... 2001, 2022

 3.4 ... average for 1659-1700 and 1992

 3.1 ... 2009

 2.8 ... 1996

 2.1 ... 1995

 0.1 ... 1981 (8th coldest December)

-0.2 ... 1874 (7th coldest December)

-0.3 ... 1788, 1796, 1878 (tied 4th coldest Decembers)

-0.5 ... third coldest December 1676

-0.7 ... second coldest December 2010

-0.8 ... coldest December 1890

-10.8 ... lowest daily mean 25th 1796

_______________________________________________

Enter your forecast before midnight on Saturday 30 November, or with the increasing late penalties for entries 1-3 Dec.

(earlier material based on CET legacy temps ...) As you might expect, the Maunder period produced cold Decembers, the mean was as low as 3.2 (1665 to 1694). It then rose as high as 4.29 by 1709-38. There was a colder period than any in the Maunder; the lowest 30-year average was 3.09 from 1783 to 1812; rounded off 1784 to 1813 was equal.

The running mean climbed as high as 4.61 for 1823-52 before falling back to 3.48 for 1867-96. Decembers in the first third of the 20th century were generally a bit milder than the mid-century period, means as high as 4.73 were reached in 1893-1922 and 1907-36. The lowest since those peaks was 4.33 for 1923-52. The last time that the running mean was 4.5 was 1957 to 1986. The table above tracks the changes since then, but worth noting that the cold December of 2010 dropped the running mean from 4.84 to 4.63 but it then went back up to 4.82 for 1982 to 2011 as that period dropped the cold December of 1981 (mean 0.3 legacy). 1981-2010 was the only 30-year mean at 4.6 after 1960-89. 

_______ _ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _ ________

 

Optional EWP (Precip) Contest -- details

The EWP contest now enters its eighth year. It remains entirely optional, in the first seven years more than two-thirds of the regular temperature forecasters entered this second contest. (there were no precip-only forecasters). This fraction has increased to about 90 per cent and scoring for combined forecasts is now regularly included.

The contest asks you to predict an amount in mm (not a percentage) for this statistic. Any forecasts entered as percentages are converted using 1991-2020 averages.

A tracker (on EWP website) gives approximate values one day late, then you will have to be patient as Hadley EWP post their final numbers around the 5th of each month. Then the practice is to tweak the numbers through the following several months, but we ignore those later adjustments for contest scoring (it would be a lot of work and very little would change). 

For December, here are the averages and extremes for your guidance. Data (from the Hadley EWP tables) go back to 1766.

The last 15 December EWP amounts appear in the table below. Both 2010 and 2012 qualified as min and max values for the period 1981-2022.

... the average of these past fifteen Decembers is 113.7 mm. It can be seen from the 30-year normals and that last figure, that a general increasing trend is underway for Dec EWP. 

 

Max 1766-2023 ____193.9 mm (1876)

Max since 1981 ___ 175.2 mm (2012)

____2023 _______ 161.3 mm

____2020 _______ 159.2 mm

____2015 _______ 145.9 mm

____2013 _______ 134.2 mm

____2019 _______ 121.4 mm

____2018 _______ 116.0 mm

____2011 _______ 113.6 mm

____2017 _______ 113.4 mm

____2009 _______ 109.1 mm

_ mean 1993-2022 _ 106.3 mm 

_ mean 1994-2023 _ 105.9 mm 

____2021 _______ 105.0 mm

Mean 1991-2020 __103.6 mm

____2022 _______ 102.2 mm

Mean 1981-2010 __ 97.4 mm

Mean 1766-2023 __ 89.4 mm (all 258 years of data)

____2014 ________ 77.3 mm

____2016 ________ 41.3 mm

Min since 1981 ___34.1 mm (2010)

Min 1766-2023 ____ 8.9 mm (1788)

____________________________________________________

Note, the highest 30-year mean of December EWP was 106.6 mm (1896-1925). The lowest was 67.5 for 1864-1893. 

Since the peak value the lowest was 84.8 mm (1925-54). It has been gradually increasing since then and is now within 0.3 mm of the earlier peak. For 1994-2023 to take over the lead, the value required was about 181 mm for 2023, because 1993 was quite a wet December at 172.1 mm. As 2023 had 161.3, the 30-year average dropped by 0.4 mm and is still below t e maximum value of 106.6. 

 

Your forecast should be in mm with one decimal allowed. If you enter a percentage, that will be applied to 1991-2020 mean of 103.6 mm to derive your contest entry. Any number that appears without a % sign or mm, will be taken as that number of mm, with .0 added. It will be up to you to clarify your contest entry.

Deadlines are the same as the temperature contest. EWP late penalties are 0.3 points per day (scoring runs from zero to 10.0 points each month).

______________________________________________________

Note that in both contests, there is a scoring deduction applied to forecasts of similar rank submitted later than others. 

We encourage you to enter each month as the contest year results depend on entering at least ten of the twelve contests. There are seasonal sub-contests which is why we start the contest year in December rather than January. Once you have missed three contests, you are no longer scored in the main CET scoring table, and while the EWP does not divide into two tables, effectively by scoring no points for three contests you are probably not going to finish among the top 20-25 total points. 

Good luck !!

 

Edited November 30 by Roger J Smith

[SteveB]

6.4c and 77mm please. 

[Earthshine]

0.0°C and 40 mm please

[Summer18]

Can’t believe I forgot this month for the first time in years! Anyway I’ll go for 4.4C and 102mm 

[Polar Gael]

4.0C and 92.0mm for me please. 

[stewfox]

4.6c 55mm

[Dancerwithwings]

5.6c and 69mm

[Catbrainz]

Going for a mild and dry Bartlett December. Seeing shades of winter 2016/2017 so far. I will shoot for 6.3c and 54mm. 

[Typhoon John]

5.9c please

[Bobd29]

6.4C and 115mm please.

[Methuselah]

5.9C and 85mm, please.

[Shillitocet]

 Earthshine I really hope that 0.0.C comes off!

[Shillitocet]

I think December 2024 will simultaneously have shades of both 2010 and 2015 in it, with a really brutal week - fortnight of cold and snow and minus double digits, however this month will flip flop to both extremes and while in the cold snap temperatures will sink below -20.C, the first 20.C of December will also hit in a ferocious storm with a very long SW stretch on a Fohn effect on steroids between Christmas and New Year, with the big day itself seeing some ridiculous temperature contrasts, with -18.C in Altnahaara early Christmas Day and some very problematic transient snow towards the North yet a plus 17.C in Plymouth on the same day giving a 35 degree swing.

   CET will be 3.3.C so below average snd actually quite wet at 99mm.

[Pulpstar]

-1 and 35 mm

[chilly milly]

5.5c and 118mm please

[Don]

 Pulpstar Good lord!! 

[Roger J Smith]

GFS for 1-6 Dec predicts 3.5 C and fairly dry 10-15 mm.

[Norrance]

5.8C and 85 mms please. 

[WYorksWeather]

 Roger J Smith Thanks Roger for the usual post. Here is my usual chart for December.

Actually remaining relatively flat since the mid-20th century, with only a very slow increase in the 30-year average, which has just ticked over 5.0C for 1994-2023. It may have accelerated in the last decade or so, but hard to tell how much of that is short term variation. Clearly the two stand-out Decembers of this century are 2015 and 2010, at opposite extremes, which are almost off the scale relative to other recent years.

The safest bet for recent Decembers seems to be between4C and 7C, but of course 2015 and 2010 prove that it can also be a very unusual month in many respects. You could argue that any guess between 0C and 10C is possible, which is probably one of the widest ranges of any month.

I will wait another week or so before making my prediction.

 

[virtualsphere]

4.1C and 85mm please

[Weather26]

6,0C and 88mm please

[I remember Atlantic 252]

7.6C and 155mm, Atlantic onslaught 1st to 31st

[johncam]

 WYorksWeather looking ominous for another mild month with latest output .

[JeffC]

4.9C and 115 mm ppn please

[Dancerwithwings]

 Pulpstar wow