December 2017 C.E.T. forecasts -- start of 2017/18 competition year -- and an optional precip contest begins

[Roger J Smith]

The temperature forecast contest continues without change of format, and we are now entering a new competition year (aligned to the four seasons as well as the calendar year 2018). 

We will start a new contest that is optional for entrants in the main temperature contest (who knows, a few NW members might want to enter only this precip contest). If you want to know more about the optional precip contest, read part 2 of this post, below the dotted line partition. If you're only into the temperature forecast, you can ignore that and enter as you always have in the past. And J10, good news for you, this precip contest will be scored separately and you don't need to do any extra work over all that work you already do scoring the temperature contest... 

with that said, here's the table of averages and extremes to guide you on the temperature forecast for December ...

 

CET averages and extremes for December

--- all CET values 1981 to 2016 are now in the table --- they are in bold italic to make them easier to find ---

 

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

 

 6.5 ... 2006

 6.4 ... 1994

 6.3 ... 1985, 2013
 6.2 ... 1986

 6.0 ... 2011, 2016

 5.9 ... has never happened in 358 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*

 5.0 ... average for 2001-2016, and 1987-2016 and 1999

 4.9 ... average for 1991-2016 (developing 1991-2020) and 1989, 2007

 4.8 ... 2003, 2012
 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 1659-2016
 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 Thursday 30 November, or take the increasing late penalties for entries 1-3 Dec.

*This 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.

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). 

 

 

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

 

Optional Precip Contest -- details

We often talk about how precip compares to normal values, but we don't track it like we track temperatures in our contest. There's nothing like a contest to sharpen our awareness (and in my case, I have not paid much attention to precip compared to CET values). I thought about using the CEP but "central England" as defined in the precip data looks considerably different, it extends east across the East Midlands into northern East Anglia. Then I thought, why not just go with national averages using England and Wales, then almost everyone is playing on home field (except for our Scottish, Irish, European and Canadian folk).

First point -- this contest is entirely optional. It won't affect scoring in the temperature forecast contest, and vice versa.

Second point -- scoring will be handled by myself, J10 has lots to do already and so this is more or less a separate contest. I would put it in a separate thread but I imagine most of those interested will be active here, and it saves you one step. 

I have chosen the "England and Wales" precip option rather than some smaller region or the larger UK precip. 

The contest asks you to predict an amount in mm (not a percentage) for this statistic.

For December, here are the averages and extremes for your guidance. Data go back to 1766.

 

Max on record ____193.9 mm (1876)

Max since 1981 ___ 175.2 (2012)

Mean 1987-2016 __ 98.3 mm

Mean 1981-2010 __ 97.3 mm

Min since 1981 ___ 34,1 mm (2010)

Min on record _____ 8.9 mm (1788)

 

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 will be based on ten points for the closest forecast, reduced as far as 9.5 if that forecast is more than 55 ranks (46-55 reduce by 0.5, and similarly down to 6-15 reducing by 0.1) different from the outcome in the table (see link at end) so the closest forecast will score 9.5 to 10.0, then each other forecast in rank order will score a step lower between that value and 0.0 for the least accurate forecast, correction could be applied but unlikely as that forecast would have to be within 55 ranks of the actual to get any boost. In each case, the most beneficial rank among ties will be used to assess the corrections.

Here's one example. Let's say for December, closest forecast is 120.0 and actual is 155.0. That would be 15th wettest, while the best forecast would be 48th wettest. The difference is 33 ranks, so best score is reduced from 10.0 to 9.7. Then if the worst forecast is any more than 55 ranks different from actual, which is likely to be the case most months, it will score 0.0, and the rest of the scores will be equally placed between 0.0 and 9.5. If the worst forecast were 45 mm, that would be 214th wettest (38th driest) and would be well outside correction range. 

Once the max and min scores are known the rest will be calculated to nearest decimal place. 

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. Only the max and min scores will depend on order of entry (in the unlikely event of ties). Non-extreme scores will not depend on when you entered relative to anyone with the same forecast error as you.

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 will only use end of month values posted, any later quality control will not be used for recalculation.

I hope we get at least one-third of our temperature regulars interested so we can have an interesting contest. Subject to cancellation if numbers not sufficient for a valid contest. 

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 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). 

[NorthYorksWeather]

5.6c

101.9mm

Cheers

[V for Very Cold]

3.9C

122.6mm

thank you

[pegg24]

5.3c 

119.1 mm

[chrisbell-nottheweatherman]

6.7C and 93.1 mm, please

[Dami]

6.2c

80.8mm - all snow

cheers and Merry Christmas 

Edited November 20, 2017 by Dami

[weirpig]

very cold December this year  and dryish    lots of northerly incursions    1.9c    41mm

Edited November 20, 2017 by weirpig

[Coldie24]

A cold start to winter - 2.1C please

[Radiating Dendrite]

3.1c and 62mm for me please.

[Methuselah]

Okay then, here we go:

4.4C and 75.0mm...

Q. What's a 'sticky note'?

Edited November 20, 2017 by Ed Stone

[BLAST FROM THE PAST]

5.8C

[Weather-history]

Junes with a CET of 16.0C or greater are frequently followed at the end of the year by a below average December. Stats quirk?

2003: 4.8

1976: 2.0

1970: 4.3

1960: 3.9

1950: 1.2

1940: 3.8

1896: 3.9

1858: 4.8

1846: 0.5

1826: 5.8

1822: 1.6

1818: 3.6

1798: 1.5

1786: 2.8

1785: 2.8

1781: 5.4

1775: 4.5

1772: 4.8

1762: 3.6

1728: 1.6

1726: 1.6

1707: 3.5

1676: -0.5

1672: 4.5

 

[simshady]

3.7c and 99.2mm please.

[Mapantz]

5.1°C and 77mm

Thank you please!

Edited November 20, 2017 by Mapantz

[LetItSnow]

2.7°C please. 

[The PIT]

December 5C and 84mm of rain.

[Roger J Smith]

4 hours ago, prolongedSnowLover said:

A cold start to winter - 2.1C please

I assume you want 2.1 and not --2.1 ... anyway use of the dash in your sentence is confusing (me). 

[Roger J Smith]

4 hours ago, Ed Stone said:

Okay then, here we go:

4.4C and 75.0mm...

Q. What's a 'sticky note'?

Not sure how your question relates to this thread but a sticky note (I think) is one of those small peel-off yellow post-it notes that somebody might use to leave a message on a door or near something that doesn't work properly. 

Speaking of which, in my explanatory note, the scoring example should have said that other scores would run between 0.0 and 9.7 (not 9.5 as it says). So consider this a thread sticky note.

Also while I'm at it, thanks for all these precip entries, it looks as though we'll have almost a full overlap which will make it more fun, I think. I should have mentioned for anyone not familiar with how precip is measured, snowfall at the various locations that are part of the EWP would be measured for its liquid equivalent, and this is usually around a 10:1 ratio so if you're expecting a snowy December keep in mind that every 10 cm of snow will only leave 10 mm of precip in the totals, for example Dec 2010 had more snow than most Decembers, little rainfall, and ended up with a monthly precip of only 34.1 mm. 

[I remember Atlantic 252]

6.2°C, dominated by the Atlantic, stormy, vile, filthy month

Edited November 20, 2017 by I remember Atlantic 252

[Weather26]

5.9c Please 

[Coldie24]

1 hour ago, Roger J Smith said:

I assume you want 2.1 and not --2.1 ... anyway use of the dash in your sentence is confusing (me). 

Haha, yes 2.1 please!

[Stationary Front]

My regular December guess for the elusive 5.9 please.

[cheeky_monkey]

im going for a below average 3.8c ...cold second half possible very cold after Xmas...im also going for a cold December here -15.5c please and thank you.

[BlueHedgehog074]

Wouldn’t mind a Canadian style December! ❄️

Not feeling convinced it will be all that cold here, to be honest. 5.6*C please, although if someone vanquished the Greenland Vortex, I’d re-adjust the estimate to -5.6*C.

[Bobd29]

5.3C and 68mm plse