A new year is near here so time for a brand new CET competition. I will start the new year with a reminder of how the CET 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. 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 generally be accepted after this time unless I am late in opening up the thread.
- 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 2016 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
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 substituted 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.
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 annual 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). However, an entry can still be made for the monthly competition even if predictions have been missed in previous months.
January historic data summary
Here is the usual rundown of historic data for previous years.
Long run averages:
1971-2000: 4.2C
1981-2010: 4.4C
1996-2015: 4.6C
January 2015 was close to average at 4.4C. 2012 and 2014 were warm at well over 5C. 2009, 2010 and 2013 were below average at 3.5C or less. 2010 was only 1.4C. 2007 and 2008 were the last very warm January's with 7.0C and 6.6C respectively.
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
Looking close to or slightly above average
Met office
http://www.metoffice.gov.uk/media/pdf/4/f/A3_plots-temp-JFM_v1.pdf
Contingency planners forecast suggests the probabilities favour a slightly above average January but the signal is not strong.
Pattern matching (JFF)
The temperatures in November and December have been unprecedented. However, if we look at other years which have seen warm conditions from October through to December we typically see mild conditions prevailing for the rest of the winter. The best comparison years are 2006 and 2011 but the sample size here is small. The main exception to this was in 1986 when it turned cold in January and stayed that way until March.
January CET graphs
Here is a first look at the January CET. Current output suggests fairly average conditions for the first 11 days overall. Just trending slightly above average. However, will feel quite chilly indeed relative to the incredibly mild conditions in December. the CET will be some 5C lower than December in the first 10 days of Jan.
Edited by moderator
15 February 2016 20:05:22
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