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

[Summer Sun]

6.9c to the 25th

2.3c above the 61 to 90 average
2.3c above the 81 to 10 average

[The PIT]

Sunny Sheffield up to 6.4C +1.4C above average, Rainfall 113.3mm 129.5% of the monthly average.

[reef]

6.9C - already joint 15th warmest despite the cold start. Another 11C+ year incoming.

What a grim month!

[Frigid]

19 minutes ago, reef said:

6.9C - already joint 15th warmest despite the cold start. Another 11C+ year incoming.

What a grim month!

Quite reminiscent to Feb 2019's progression in the CET. It's been grim since the 5th with the odd cold night. Last 10 days have seen max temps above 10C. This month has pretty much been an inverse of last month. Strangely getting milder as the month progressed. 

[Typhoon John]

I thought my 7c was going to be way too high. I had meant to revise it down a bit once the cold start was on the cards. I'm pleased I forgot to now.

[Rheidolinflood]

4 hours ago, reef said:

6.9C - already joint 15th warmest despite the cold start. Another 11C+ year incoming.

What a grim month!

Not so bad for those of us who have to pay the heating bills.

[LetItSnow!]

Hoping that December 2023 will be to January 2024 what December 1986 was to January 1987... a colder February than in 1987 would be nice to follow though!

[Roger J Smith]

EWP is around 111 mm at present and looks to finish 145-150 mm. At 150 mm annual total will be 1183 mm ranking 7th just behind 1960 (1195.0 mm) and well ahead of 1903 (1160.3). As of today the year is passing 9th place 1877 (1144.1) and 8th place 1882 (1146.2). We passed tenth place 1848 (1130.1 mm) a few days ago. So it looks like either 7th or possibly 6th as 5th is a bit out of reach probably (1852_ 1213.0 mm), it would require 180 mm for Dec (or substantial edits of Oct-Nov table values as the EWP values are adjusted several times before settling). 

Rest of top ten is fourth wettest 2000 (1232.4 mm), third wettest 2012 (1244.4 mm), second 1768 (1247.3 mm) and first 1872 (1283.9 mm). 

Keep in mind it was very dry in Feb 2023 (16.5 mm). Of the years in current top ten, the driest month any of those had was 12.8 mm in march 1768, followed by 17.1 mm in march 1852, several others had no totals below 30 and 1872 had a low value of only 66.2 (in may). It seems to be common for wet years to do most of their business in second half of year with perhaps one or two wet months before July. This may be because average values are higher for January and the last four months of the calendar year. 

CET output now looks a bit colder again, and would end up about 6.7 on today's guidance. Looks very windy for night of 30-31 Dec. 

[Roger J Smith]

Two more CET daily records fell on 25 Dec, mean daily 10.7 breaks 10.4 (1824) in v2.0, it was tied w1983 in CET legacy but 1983 became 10.2 in v2.0. 

Also minimum of 10.1 broke 9.1 from 1983. 

The max of 11.3 was not a record.

The count for high mean daily records in 2023 is now 10.5 ... now tied with 1947 and 2011 for most daily records.  2022 had 9.5.

1947 also had 5.0 low mean daily records; none of the other years mentioned had any. 1895 is another year with a significant count in both categories (4.0 and 7.0). 

The years with the highest count of low daily records (v2.0) are 1816 and 1841 both with 9.5. 1812 has 8.5. 

Edited December 27, 2023 by Roger J Smith

[The PIT]

The first pause for a while. Sunny Sheffield still at 6.4C +1.4C above average. Rainfall 129.1mm 147.5% of the monthly average.

[Summer Sun]

6.8c to the 26th

2.3c above the 61 to 90 average
2.2c above the 81 to 10 average

[The PIT]

Sunny Sheffield remains at 6.4C +1.5C above average. Rainfall 138.5mm 158.3% of the monthly average.

[Summer Sun]

6.9c to the 27th

2.4c above the 61 to 90 average
2.4c above the 81 to 10 average

[WYorksWeather]

Based on figures from now to the end of the year, it looks like we're going to be roughly in a holding pattern. Maybe a slight rise to 7.0C after a mild day today is possible, then staying the same or a slight fall. Don't think it'll move very much now, a finish probably in the 6.8-7.0C range.

[Harveyslugger]

On 19/11/2023 at 09:42, Roger J Smith said:

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 !!

 

3.7c and 72mm please

[Dancerwithwings]

1 hour ago, Harveyslugger said:

3.7c and 72mm please

December is too late ….You need to go to 

 

 

[Summer Sun]

7.0c to the 28th

2.5c above the 61 to 90 average
2.5c above the 81 to 10 average

[Metwatch]

CET is at a balmy 7C now which makes it as mild as March, and just a little bit below November this year.

It's ahead of April 2021 by 0.5C now. If you want to know how many October's have been colder than this month, it would be around 6, with 1896 last having a sub 7C October CET.

it looks like December 2023 will be the second warmest December of this century if it can stay above 6.8C, which was December 2018's CET. However December 2015 is still in a league of its own.

Edit: Answering your Q @snowray doesn't look like there has been!

Edited December 29, 2023 by Metwatch

[snowray]

39 minutes ago, Metwatch said:

CET is at a balmy 7C now which makes it as mild as March, and just a little bit below November this year.

It's ahead of April 2021 by 0.5C now. If you want to know how many October's have been colder than this month, it would be around 6, with 1896 last having a sub 7C October CET.

it looks like December 2023 will be the second warmest December of this century if it can stay above 6.8C, which was December 2018's CET. However December 2015 is still in a league of its own.

Looking at your list there, can I ask, has there ever been a 7c December?

[Optimus Prime]

Hideous month. Not quite as bad as 2018 due to the chilly start. 

[TillyS]

That’s quite a jump again and I ‘think’ it will hold fairly steady now. Today’s temps will be offset by a cold-ish night but then probably around the 7C mark for the last two days.

It’s incredible to see all the shoots up and trees coming into bud. I even saw cherry blossom out in Surrey today.

[The PIT]

Sunny Sheffield up to 6.5C +1.7C above average. Rainfall up 141.9mm 162.2% of the monthly average.

Fifth warmest December on record here and looks likely to stay there. Likely to be the sixth wettest on record. It may make the 5th wettest. The year 2nd wettest on record here since 1954. Unless we get 70+ mm of rain tomorrow which isn't going to happen.

[summer blizzard]

1 hour ago, snowray said:

Looking at your list there, can I ask, has there ever been a 7c December?

See the post just above yours, yes. 

With 14 out of ~300 years of records it's about once every 25 years. 

[Scorcher]

19 minutes ago, summer blizzard said:

See the post just above yours, yes. 

With 14 out of ~300 years of records it's about once every 25 years. 

I think the question might have been whether there has been a 7.0C month on the button- which there hasn't. Plenty of 7C+ Decembers though yes.

[TheOgre]

How warm does this month need to be for 2023 to be warmer than 2022?