2015 is nearly upon us so time for a brand new CET competition following what looks like being a record breaking 2014. As ever I will start the new year with a reminder of how the various 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 (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 2015 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 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 6 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 2014 the January CET was 5.7C, the warmest since 2008. In 2010 it was just 1.4C, the coldest since 1987. 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/MT2_Manchester_ens.png
http://www.wetterzentrale.de/pics/MT8_Manchester_ens.png
850 temperatures look very average overall throughout although T2m temperatures probably slightly above average
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=tx
http://www.knmi.nl/exp/pluim/kansverwachtingen_staafdiagram.php?run=00&type=tn
Temperatures likely to be a little above average for the first part of January.
Weatheronline
http://www.weatheronline.co.uk/cgi-app/reports?MENU=Month-ahead
Generally on the cool side possibly colder later. Rather unsettled especially in the north.
Met office
http://www.metoffice.gov.uk/media/pdf/5/9/A3_plots-temp-JFM.PDF
Contingency planners forecast suggests a very average Jan to March period but with lots of uncertainty. Greater likelihood of blocking occurring later in January but this does not necessarily mean a period of sustained cold for the UK.
http://www.metoffice.gov.uk/public/weather/forecast
30 day forecast suggests average or slightly above average temperatures.
Pattern matching (just for fun)
Looking at years since 1900 with a similar temperature profile to 2014 in the final two to three months and particularly the final two months there are only a few matches. The years in question are 1959, 1984, 1986, 1997, 2006 and 2011.
What we see is that the following January and February temperatures in those years vary considerably so no obvious pattern. If we also consider the QBO in those years we get a slightly different picture. Most years with a positive or neutral QBO see average or above average temperatures in January and February. However, negative QBO years tend to be cold (e.g. 1984 and 1986).
But there are some exceptions. 2011 is the most obvious as it had a very negative QBO but a warm winter. Why? Well no doubt a number of factors were involved but if we consider sunspot numbers we see that those years with a negative QBO but relatively high sun spot numbers did not tend to have a cold winter (such as 2011).
The two best analogue years to 2014 are 1984 and 2011. The QBO in 2014 is much closer to 2011 as it is more heavily negative. The sun spot numbers are also much more aligned to 2011. The December 2011 figure was around 70 on average which is similar to what we are seeing this year. In 1984 sun spot numbers were only 19 in December.
So 2011 is clearly the best fit and in fact 2011 temperatures are almost identical to 2014 all the way back to August. It is true that November and December 2011 were a bit warmer but generally a very good fit. What we saw at the start of 2012 was an above average January but a slightly below average February.
In fact there was a sustained cold spell between 29 Jan 2012 and 12 Feb 2012. In this period the mean CET was -0.6C and the CET never exceeded 2.2C. There were 10 days where the CET was negative.
For 2015 the first third of January looks like it will be above average and possibly quite a bit above average. That would follow the pattern of 2012. The suggestions of a weakening of the positive NAO during the latter part of January plus the possibility of a SSW might increase the chances of a cold spell towards the end of January similar to what we saw in 2012.
Given the consistent modelling we have been seeing in recent days for the start of January I think there is a greater than average chance of a warm month albeit it might turn cooler later on.
Edited by moderator
09 February 2015 13:50:17
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