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December 2020 C.E.T. and EWP forecast contests -- start of the new contest year for 2020-2021


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On behalf of J10 and myself, welcome to another new competition year with the winter season of 2020-21 fast (?) approaching (??). The contests will include the CET forecast and the (still optional) EWP forecast, with some guidance provided in two sections below ... 

 

CET averages and extremes for December

--- all CET values 1981 to 2019 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 the 39 most recent years. 

 

13.1 ... warmest daily mean, 19th 2015

12.9 ... previous warmest daily mean, 12th 1994

 9.7 ... warmest December 2015
 8.1 ... tied second warmest Decembers 1934 and 1974
 7.7 ... fourth warmest December 1852

 7.6 ... fifth warmest December 1733

 7.5 ... 1988

 6.9 ... 2018

 6.5 ... 2006

 6.4 ... 1994

 6.3 ... 1985, 2013

 6.2 ... 1986

 6.0 ... 2011, 2016

 5.9 ... has never happened in 361 tries

 5.8 ... 1997, 2000, 2019

 5.7 ... 2002

 5.6 ... 1983, 1987

 5.5 ... 1993, 1998

 5.4 ... 2004

 5.2 ... 1984, 2014

 5.1 ... average for 1971-2000* and 2001-19

 5.0 ... average for 1990-2019, 1991-2019 (developing 1991-2020) and 1999

 4.9 ... 1989, 2007

 4.8 ... 2003, 2012, 2017

 4.7 ... average for 1961-90 and 1991

 4.6 ... average for 1981-2010, also 1901-2000

 4.4 ... 1982, 2005

 4.3 ... 1990

 4.1 ... average for 1659-2019 (all 361 years)

 4.0 ... average for 1801-1900

 3.9 ... average for 1701-1800

 3.6 ... 1992, 2001

 3.5 ... 2008

 3.4 ... average for 1659-1700

 3.1 ... 2009

 2.9 ... 1996

 2.3 ... 1995

 0.3 ... 1981

--0.4 ... tied fourth coldest 1788 and 1796
--0.5 ... third coldest 1676
--0.7 ... second coldest 2010
--0.8 ... coldest December 1890

-10.8 ... lowest daily mean 25th 1796

_______________________________________________

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

*1971-2000 is in fact the highest 30-year average for December in the CET series, and the only one that rounds to 5.1, from 5.06. With the exception of June, this is the furthest back one has to go to find the maximum value. For most months it is one of the past four (1987-2016, 1988-2017, 1989-2018 or 1990-2019). For June, however, it was 1822-51 (14.72) followed closely by an earlier peak, 14.70 for 1772-1801. 

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. 

_____ _ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _ ________

 

Optional Precip Contest -- details

The EWP contest now enters its third year. It remains entirely optional, in the first two years about two-thirds of the regular temperature forecasters entered this second contest. (there were no precip-only forecasters). 

The contest asks you to predict an amount in mm (not a percentage) for this statistic. Any forecasts entered as percentages are converted using 1981-2010 averages.

After using the 1910-2017 "NCIC" precip values for the first contest, and scoring Hadley as an alternative, I went with the somewhat later appearing Hadley values for the second contest year, to reduce the complexity of scoring and reporting. You will have to be patient as Hadley posts their numbers around the 5th of each month. Preliminary numbers are available on the 2nd of each month and they rarely change much when given a decimal. Then the practice is to tweak the numbers through the following several months, which led me to start an "ultimate scoring" alternative table that adjusts the contest scores by these later amended values. However, the first reported values are what we use for the official contest results. In any case, most people stay within one rank or at the most two ranks of where they were in the immediate scoring. 

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

The last ten December EWP amounts appear in the table below. Both 2010 and 2012 qualified as min and max values for the period 1981-2018.

... the average of these past ten Decembers is 107.2 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 on record ____193.9 mm (1876)

Max since 1981 ___ 175.2 mm (2012)

____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 2010-19 __ 107.2 mm

Mean 1990-2019 __ 101.5 mm

Mean 1981-2010 __ 97.4 mm

Mean 1766-2019 __ 88.6 mm (all 254 years of data)

____2014 ________ 77.3 mm

____2016 ________ 41.3 mm

Min since 1981 ____34.1 mm (2010)

Min on record _____ 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 5 mm of the earlier peak. 

 

Your forecast should be in mm with one decimal allowed. If you enter a percentage, that will be applied to 1981-2010 mean of 97.3 to derive your contest entry. Any number that appears without a % sign 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.

Scoring rules (general summary) ....

Top score will be 10.0 regardless of error. Lowest score will be 0.0, and all other scores will be calculated from step values. This contest year, order of entry will affect your score, but each later (equal ranked error) forecast will drop by 0.1 rather than the full step value (which is often 0.2 or 0.3). The lower scores after these ties will resume at a point determined by full step value drops. Example, three are tied at 7.0 by step values, so they score 7.0, 6.9 and 6.8. Then the next score will be 6.4 (as though three steps had been used). Forecasts with equal errors on either side of an actual value (example, 60.0 and 80.0 with actual 70.0) will score the same, and their respective later entries will also score the same as each other (if both have duplicate entries).

Late penalties are applied as follows: 0.2 per day late. Example, you score 8.4, but enter on second late day, penalty of 0.4 reduces that score to 8.0. No score will be negative after this rule applies.

The table of ranked monthly amounts (for EWP) can be found here. With a bit of navigating you can also find other products of the precip product. The contest scores are based on the earliest posted table values and when those change slightly as they tend to do within 3-4 months, ultimate scoring section below the main contest scoring in the excel file will alert you to how your score would have changed (but the ultimate contest scoring is not to be considered official).

I hope we get an even stronger contingent of our temperature regulars involved in this precip forecast. 

Reference:

http://hadobs.metoffice.com/hadukp/data/ranked_monthly/HadEWP_ranked_mly.txt

If entering both contests, just post once (not a requirement, you can post separate forecasts but try to remember to use mm)

A sample "good" entry would be

5.0 C, 82.5 mm

(that's not my entry, I will enter around the 30th). Order of contest posting can become different for CET and EWP if a forecaster changes one but not the other forecast earlier submitted.

Good luck and thanks again on behalf of all of us to J10 for scoring and administering the temperature forecast contest. 

He may want to let you know about any scoring changes planned for 2020-21,  The CET scoring awards points for various measures of accuracy and you need to enter at least eleven

of the twelve contests to be ranked in the table at the end of the contest year. 

 

Good luck to all entrants !! 

Edited by Roger J Smith
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20 minutes ago, Stationary Front said:

5.9 it will be so this year! With 85mm

Or 9.5! 😨

Not my guess at this stage! 😉

Edited by Don
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  I think its going to be disgustingly mild....worse than the infamously mild December 2015. 10.3.C (a new record) with a ridiculously mild feed around Winter Solstice....I see temperatures hitting 20.C on the 20th in 2020 making for a great headline. Check climate reanalyser out, as of 19th Nov the Arctic area anomaly is an outrageous +6.7.C and thats with respect to 1980-2000! Rainfall roughly 100mm

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I think something similar to 2017.  Some spells of cold but unsure as to whether the frosty or snowy type yet.  Not always long lived though and there will be a mild period lasting at least several days.

5.0C and 115mm

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3 hours ago, Shillitocettwo said:

  I think its going to be disgustingly mild....worse than the infamously mild December 2015. 10.3.C (a new record) with a ridiculously mild feed around Winter Solstice....I see temperatures hitting 20.C on the 20th in 2020 making for a great headline. Check climate reanalyser out, as of 19th Nov the Arctic area anomaly is an outrageous +6.7.C and thats with respect to 1980-2000! Rainfall roughly 100mm

Wasn't far off last year, reached 18.7°C in Scotland.  Foehn effect works wonders up there.

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Rest in pieces 2020!  Also rest in pieces bloody COVID19 and please naffoff for good!  Also 12C  😞  Last sub 0C, last sub 1C, last sub 2C, last sub 3C and last sub 4C December all in 2010.

200mm of Atlantic garbage

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On 20/11/2020 at 07:52, Lettucing Gutted said:

Rest in pieces 2020!  Also rest in pieces bloody COVID19 and please naffoff for good!  Also 12C  😞  Last sub 0C, last sub 1C, last sub 2C, last sub 3C and last sub 4C December all in 2010.

200mm of Atlantic garbage

5 years since you underestimated the December CET!  Wonder if you'll be under again this year?... 😂

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