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December 2019 C.E.T. and EWP forecast contests -- start of the 2019-2020 competition year

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  • Location: Rossland BC Canada
  • Location: Rossland BC Canada

On behalf of J10 and myself, welcome to another new competition year with the winter season of 2019-20 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 2018 are in the table --- they are in bold type to make them easier to find

--- --- --- and colour coded for warmest, middle and coldest thirds of the 38 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 360 tries

 5.8 ... 1997, 2000

 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 2001-18

 5.0 ... 1999

 4.9 ... average for 1989-2018, 1991-2018 (developing 1991-2020) and 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 1659-2017 (all 360 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 Saturday 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. June 2018 was warm enough to boost the running 30-year average to 14.64, its highest value since 1825-54. In between the peaks, the June average got as low as 13.8 (1900-29), rising to 14.57 for 1931-60 and 1932-61, then falling back to 14.07 as recently as 1971-2000. June 2019 resulted in a slight drop of the running June 30-year average, to 14.63. 

The running 30-year December mean actually dropped fractionally (staying 4.9) because very mild 1988 was replaced by almost as mild 2018.

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 106.0 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

____2018 _______ 116.0 mm

____2011 _______ 113.6 mm

____2017 _______ 113.4 mm

____2009 _______ 109.1 mm

_ mean 2009-18 __ 106.0 mm

Mean 1989-2018 __ 102.5 mm

Mean 1981-2010 __ 97.4 mm

____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 4 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 whole number of mm. 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. 



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 plans for 2019-20, 


Good luck to all entrants !! 

Edited by Roger J Smith
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  • Location: Weston-S-Mare North Somerset
  • Weather Preferences: Hot sunny , cold and snowy, thunderstorms
  • Location: Weston-S-Mare North Somerset

6.1c and 140mm please. 

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  • Location: Broxbourne, Herts
  • Weather Preferences: Snow snow and snow
  • Location: Broxbourne, Herts


Upping my game on the rainfall..... I'm going for 143mm (this almost guarantees that my usual 77mm will come in this month!)


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  • Location: Edmonton Alberta(via Chelmsford, Exeter & Calgary)
  • Weather Preferences: Sunshine and 15-25c
  • Location: Edmonton Alberta(via Chelmsford, Exeter & Calgary)

5.9c just because it has never happened before and 85mm rain somewhere

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  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

4.4 C and 91.4 mm please 

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  • Location: Redlynch, Wiltshire / 110m asl
  • Weather Preferences: Cold snowy winters, warm springs, hot summers, warm then stormy autumn
  • Location: Redlynch, Wiltshire / 110m asl

7.0C and 105.7mm.. wet theme continuing with south westerlies throughout the month, cold snap before New Year not bringing mean down a lot

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  • Location: Hertfordshire
  • Weather Preferences: SNOW AND FREEZING TEMPS
  • Location: Hertfordshire
Just now, Steve Murr said:


Dry 70mm

Wow 2.7 Steve . I hope your right mate ??

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  • Location: Yorkshire Puddin' aka Kirkham, Lancashire, England, United Kingdom
  • Weather Preferences: cold winters, cold springs, cold summers and cold autumns
  • Location: Yorkshire Puddin' aka Kirkham, Lancashire, England, United Kingdom

Rest in pieces 2019!  Also rest in pieces 2000s!  Also rest in pieces 2010s!  12C  :oldsad:  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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  • Location: Trowbridge, Wilts
  • Weather Preferences: hot summers; frigid winters; golden fall; bright spring
  • Location: Trowbridge, Wilts

4.6 and 78mm please

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  • Location: Redhill, Surrey
  • Weather Preferences: Southerly tracking LPs, heavy snow. Also 25c and calm
  • Location: Redhill, Surrey

I’m waiting.....I’m strongly of the mind of sub 3c.....and of the mind of sub 2c...but also know it’s knife edge



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  • Location: Comrie, Perthshire, Bonnie Scotland
  • Weather Preferences: Winter: bright & frosty/snowy; summer: hot and sunny.
  • Location: Comrie, Perthshire, Bonnie Scotland

3.0°C and 88.0mm for me please. 

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