December 2023 C.E.T. and EWP forecast contests -- start of 2023-24 contest year -- all welcome

[Roger J Smith]

On behalf of J10 and myself, welcome to another new competition year with the winter season of 2023-24 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 six 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 2022 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 42 most recent years. 

--- --- --- due to ties for 4.8 C there are 15 in total among the middle third and 12 for the coldest, 14 for the mildest. 

... all values in the CET contest have been converted to v2.0, including the averages for various intervals. 

 

13.0 ... warmest daily mean, 19th 2015

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

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

 9.6 ... 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

 7.3 ... 1988 (tied ninth warmest with 1857, 1898)

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

__ values and ties outside modern interval no longer noted, 7.0 and 7.1 have no instances in v2.0 __

 6.8 ... 2018

 6.4 ... 2006

 6.3 ... 2013, 2021

 6.2 ... 1985, 1994

 6.1 ... 1986

 5.9 ... 2011, 2016 (in CET legacy there never was a 5.9 recorded, now also with 1977 there are three)

 5.7 ... 1999, 2019

 5.6 ... 2002

 5.4 ... 1983, 1987, 1998, 2000

 5.3 ... 1993, 2004

 5.1 ... 1984, 2014

 5.0 ... average for 2001-22

 4.9 ... average for 1971-2000, 1993-2022, also 2007, 2020

 4.8 ... average for 1991-2020, also 1999

 4.7 ... 1989, 2012, 2017

 4.6 ... average for 1901-2000 and 2003

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

 4.3 ... 2005

 4.1 ... 1982, 1990

 4.1 ... average for 1659-2022 (all 364 years, 4.10 C)

 4.0 ... average for 1801-1900

 3.9 ... average for 1701-1800

 3.5 ... 2008

 3.4 ... 1992, 2001, 2022

 3.4 ... average for 1659-1700

 3.1 ... 2009

 2.7 ... 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 Thursday 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). 1981-2010 was the only 30-year mean at 4.6 after 1960-89. 

(note, v2.0 means have dropped 0.1 to 0.2 from CET legacy values, in recent decades. Dec 2000 dropped by a larger amount due to large adjustments during a cold spell near the end of the month -- this may explain why some of the values in the table appear to be "off" slightly from what you might recall from the CET legacy numbers, for example, 2015 used to average 9.7, and 1934 used to be tied with 1974 at 8.1 ... Dec 1981 has fallen from a mean of 0.3 to 0.1 in the new set). Note: updated to v2.0.1.0.

 

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

 

Optional EWP (Precip) Contest -- details

The EWP contest now enters its seventh year. It remains entirely optional, in the first six 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 fourteen 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 fourteen Decembers is 110.5 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 1766-2022 ____193.9 mm (1876)

Max since 1981 ___ 175.2 mm (2012)

____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

_ mean 2009-22 __ 110.5 mm

____2009 _______ 109.1 mm

_ mean 1993-2022 _ 106.3 mm 

____2021 _______ 105.0 mm

Mean 1991-2020 __103.6 mm

____2022 _______ 102.2 mm

Mean 1981-2010 __ 97.4 mm

Mean 1766-2022 __ 89.1 mm (all 257 years of data)

____2014 ________ 77.3 mm

____2016 ________ 41.3 mm

Min since 1981 ___34.1 mm (2010)

Min 1766-2022 ____ 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. Although Dec 2022 had a near average total, it replaced 1992 in the recent 30-year average and added 23.6 mm to that value, resulting in a slight rise. For 1994-2023 to take over the lead, the value required will be about 181 mm because 1993 was quite a wet December at 172.1 mm. 

 

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 19, 2023 by Roger J Smith

[JeffC]

3.0C and 110mm please

[Weather26]

4.4C and 85mm please

[Bobd29]

5C and83mm please

[alexisj9]

4.1cet, 81 mm

[Polar Gael]

4.0°C and 126.5mm for me please.

[Methuselah]

4.9C and 88mm please, Roger.

[virtualsphere]

6.0C and 136mm please.

[moorlander]

5.1c and 96mm 

Personally i would like the first figure to be a lot lower in reality

[John88B]

4.2c and 80mm please.

[Gazse9]

4.2C and 72mm

[SteveB]

5.1c and 63mm please. 

[Typhoon John]

7c please

[stewfox]

3.8c 75mm

[chilly milly]

5.5c and 118mm please

[Leo97t]

4.9c.  and 70mm

[Earthshine]

5C and 80mm please

 

[damianslaw]

Reflecting on Decembers since the infamous cold December 2010.

One thing I've noted is how all Decembers since have brought very mild or at least average/ just above average mean temps in the week leading up to christmas i.e. 18 -25 Dec, sometimes this theme has extended to New Year, 2022 a great example.

Interested to know whether said period has been the mildest week of each Dec since 2010.

I always hope for cold in the run into christmas, but its been snatched away many times recently, 2008, 2012, 2017, 2022 and 2023. Indeed we've had quite a few cold starts to Dec.. 2023 could well do the same, typically!

Edited November 23, 2023 by damianslaw

[Roger J Smith]

Going back in CET records, these are the coldest consecutive judged by the value they both fell below (their average in brackets): 

 

Cold consecutive Dec _______________ notable cold average of two but not qualifying in first list

2009-10 __ 3.1 -0.7 __ 3.1 (avg 1.2)

1995-96 __ 2.1 2.7 ___ 2.7 (avg 2.4) __ 1981-82 avg 2.1 (0.1 4.1)

1962-63 __ 1.8 2.6 ___ 2.6 (avg 2.2)

1961-62 __ 2.2 1.8 ___ 2.2 (avg 2.0) __ 1927-28 avg 2.8 (2.1 3.4)

(1916-17 __ 1.9 2.3 ___2.3 (avg 2.1)) __ 1889-90 avg 1.3 (3.3 -0.8)

1878-79 ___-0.3 0.7 ___0.7 (avg 0.2) __ 1886-87 avg 2.3 (1.9 2.6)

(list now all significant close calls as 1878-79 is lowest for both values)

(1869-70 ___ 2.8 0.6 __ 2.8 (avg 1.7)) __ 1874-75 avg 2.0 (-0.2 4.2)

(1859-60 ___ 1.6 1.2 __ 1.6 (avg 1.4))

(1829-30 ___ 1.4 1.8 __ 1.8 (avg 1.6))

(1807-08 ___ 1.9 2.2 __ 2.2 (avg 2.1))

(1798-99 ___ 1.5 1.3 __ 1.5 (avg 1.4)) __ 1787-88 avg 1.8 (3.8 -0.3) __ 1783-84 avg 1.5 (2.7 0.3)

before that, the lowest values 1685 to 1782 are all quite moderate:

(1764-65 ___ 2.8 1.7 __ 2.8 (avg 2.3)) ___ 1727-28 avg 2.6 (3.6 1.6) and 1726-27 avg 2.7 (1.8 3.6)

(1696-97) ___2.5 2.5 __ 2.5 (avg 2.5)) ___ 1715-16 avg 2.3 (1.5 3.0)

 

earlier in the maunder min, we find lower values again

(1676-77 ___ -0.5 2.0 __ 2.0 (avg 0.8)) ___ 1683-84 avg 2.3 (0.5 4.0) 

(1677-78) ___2.0 0.5 ___ 2.0 (avg 1.3) ____1678-79 avg 1.5 (0.5 2.5)

____ ____ ____ ____ ____ ____ ____ ____ ____ 1679-80 avg 1.8 (2.5 1.0), 1680-81 avg 2.0 (1.0 3.0)

 

So, 2009-10 beat all but two pairs for low average CET. (1676-77 second lowest average)

Since 2010 the lowest values not including 2010-2011 (-0.7 5.9) avg 2.5 are 5.7 4.9 for 2019-2020 for value exceeded (5.7),

and 6.3 3.4 for 2021-22 for low two-year average of 4.9. Any value below 5.7 for 2023 will improve on both of those.

 

____________________________________________

Note, list is successively colder going back in records to 1878-79, with one notable case in brackets out of that sequence

The list is not successively colder for average of two, in fact 2009-10 is colder for that, than all pairs since 1878-1879, edging out 1889-1890. 

I will post forecasts later and will then delete this post and place it in discussion portion after 2nd Dec.

Edited November 24, 2023 by Roger J Smith

[Polar Gael]

On 20/11/2023 at 13:27, Polar Gael said:

4.0°C and 126.5mm for me please.

Revising this to 2.0°C and 96.5mm please. Thanks!

[syed2878]

December will be quite mild. For December I'm going for 6C and rain 50MM.

[Summer18]

4.2 and 88mm 

[WYorksWeather]

As I did in November, for those who prefer a visual aid, here are all of the December CET values.

The striking thing is just how large an anomaly both 2010 and 2015 were. 2010 being the first sub-zero December in more than 100 years, and 2015 being the warmest by a huge margin.

Legend:

Lighter blue / cyan is the 10-year trailing average (i.e. 2000 = average of 1991-2000)

Dark blue is the  30-year trailing average (i.e. 2000 = average of 1971-2000)

 

You can see that the 30-year average is slowly trending upwards, but the 10-year average is much more chaotic, with a much greater number of peaks and troughs.

I'll wait to deliver my own prediction until modelling is a bit clearer on early December.

[The PIT]

I'm going for 5.8C and 80mm of rain.

[Dancerwithwings]

4.9c & 59mm