We come to the end of another year and so time for a brand new annual CET competition as well as the usual monthly competition. As ever I will start the new year with a reminder of how the competitions work for the benefit of everyone but also anyone who would like to join in for the first time. All are welcome to participate.
How do the competitions work?
Each month a new thread is opened a few days in advance of the start of a new month. Your challenge is to predict the mean Central England Temperature (CET) for the following month. The CET is the longest running temperature series and goes back to the mid 1600's. Each month I post some statistics about the CET for that month in recent years as well as a summary of some of the latest model output and long range forecasts to provide some context to assist you in making your prediction.
Predictions can be made either to one or two decimals (the actual data is published to two decimals). The closest person or persons to the final figure at the end of the month are declared the winner for that month. There are no prizes. This competition is just a bit of fun and the chance to amaze your fellow posters with your skill and foresight in predicting the weather (or you can just make a random guess!).
We use the Hadley data for the purposes of this competition which is maintained by the Met Office. Provisional figures are published daily with a final adjusted number usually issued on the first day of the following month. Other CET series are available (such as that maintained by Philip Eden) but are not always updated daily which is the main reason why we use Hadley.
In addition to the monthly competition there is an annual competition which runs throughout the year (this is different to the one off up-front annual CET prediction competition which is in a separate thread). The annual competition keeps a running total of the cumulative prediction errors from each month for each person. Absolute differences are used so it makes no difference if you overpredict or underpredict the CET in any given month. At the end of the year the person with the lowest cumulative prediction error after totalling each of the 12 months is declared the winner for the year. This is always a hard fought contest and requires a consistency of good predictions in order to win.
Summary of important rules
- For the monthly competition predictions can be made up to 23:59 on the 2nd day of the month to which the prediction relates. No entries will be accepted after this time.
- For the annual competition predictions must be made by 23:59 of the final day of the preceding month in order to avoid penalties. However predictions can still be made up to 23:59 on the 2nd day of the month to which the prediction relates.
- All predictions should be made in the CET thread for the relevant month where possible (except for the final two months of the year - see below). As the thread is usually only opened 3 or 4 days before the end of the month, if you expect to be away or unable to post for any reason you can send me your prediction earlier by way of private message and I will post it in the thread when it is opened.
- Predictions for November and December are to be made by private message to me. This is to avoid tactical predicting at the end of year rather than predictions based on expectations of the weather. The purpose of the competition is to predict what you think the temperature will be not to protect your position in the league table.
- Once you have posted your prediction you are only permitted to change it once. Any subsequent amendments will be ignored. No amendments are allowed after 23:59 on the last day of the month
- You may make a prediction to either one or two decimals. You can predict the same figure as someone else.
- Late entries are subject to a penalty for the purposes of the annual competition. For 2014 the penalties will continue to be 0.2C for each day the entry is late (i.e. an entry made on the 2nd of the month will incur a penalty of 0.4C).
- Where two members have the same cumulative prediction error for the year at the end of any month, the order of ranking in the competition table will be determined by which person has had the closest prediction to the actual CET in any month. If there is a still a tie I then look to the second closest prediction for each person and so on until the tie is broken. If the tie cannot be broken (very unlikely by December but can happen in the first couple of months of the year) then each person impacted is awarded the same position in the table.
Missed predictions
Prior to 2013 anyone who did not make a prediction in every month of the year became ineligible for the annual competition. This was changed last year as there are sometimes unforeseeable reasons that prevent people making a prediction in time. The following rule applies where a prediction is not made in time:
If a person in the annual CET competition does not make a prediction in any one month (including January) their prediction error for that month will be calculated as follows:
- the upper quartile (75th percentile) of the prediction errors of all the people in the annual competition who did make a prediction for that month will be calculated at the end of the month;
- the normal penalty for a late prediction on the 2nd of the month (i.e. 0.4C) will be added to the figure above
The result of the above calculation will be used as the CET prediction error for any person who misses a prediction in a particular month subject to one further point:
- If, for any person, their average monthly prediction error for all the previous months in the year to date is higher than the 75th percentile of errors (for those that did make a prediction) in the month the person in question made no prediction, then the average prediction error will be substitued instead of the 75th percentile figure. The 0.4C penalty will still be added on top. This override is only likely to apply to those people towards the foot of the table who have very made very large errors in previous months.
While the above may sound a little complicated it is very easy to calculate on a spreadsheet and seems to have worked fairly well in 2013.
One final important point. No one person may miss more than two predictions during a calendar year. If a third prediction is missed that person will be eliminated from the competition (otherwise it would mean 25% or more of the annual error being calculated on non-existent predictions which would reduce the credibility of the competition too much).
January historic data summary
Here is the usual rundown of historic data for previous years.
4 of the last 5 January's have seen a CET more than 0.5C below the 1971-2000 mean.
Long run averages:
1971-2000: 4.2C
1981-2010: 4.4C
1989-2013: 4.7C
In 2013 the January CET was 3.5C. In 2010 it was just 1.4C. However, in 2007 and 2008 we saw a CET of 7.0C and 6.6C respectively. So plenty of warm and cold January's in recent years.
Here is a chart of the January CET since 1961 with a 10 year moving average
Here are some details of what the models and forecasters generally are saying at the moment.
GEFS (850 and 2m temps)
http://www.wetterzentrale.de/pics/MT8_London_ens.png
http://www.wetterzentrale.de/pics/MT2_London_ens.png
http://www.wetterzentrale.de/pics/MT8_Manchester_ens.png
http://www.wetterzentrale.de/pics/MT2_Manchester_ens.png
Looks fairly average overall throughout if not slightly above average at 2m temperature level
ECM(De Bilt) maximum and minimum temps
http://www.knmi.nl/exp/pluim/vijftiendaagse/index.php
http://www.knmi.nl/exp/pluim/kansverwachtingen_staafdiagram.php?run=00&type=tn
http://www.knmi.nl/exp/pluim/kansverwachtingen_staafdiagram.php?run=00&type=tx
Above average at first but trending down towards average.
Weatheronline
http://www.weatheronline.co.uk/cgi-app/reports?MENU=Month-ahead
Turning cold by mid month after a relatively mild start. Perhaps turning milder in the south by the end of the month.
Met office
http://www.metoffice.gov.uk/media/pdf/i/i/A3_plots-temp-JFM.pdf
Close to average or just above
Pattern matching (just for fun)
We may end up with December 2013 being warmer than November. This has happened fairly often historically although the last time was back in 1993 and it has only happened three times since 1943.
Looking back at the records when December was warmer than November and the December CET was around 6 - 6.8C typically the January CET came in within about +-0.5C of the 1971-2000 mean. This is consistent with the Met Office contingency planners forecast. So something between about 3.5C and 4.7C seems the most likely range for where the Jan 2014 CET will come in based on the pattern matching alone.
Edited by moderator
05 February 2014 22:30:42
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