Apologies for the late start to this thread.
September has been a very cool month - the coldest for over 20 years and continues the theme of rather cool weather we have seen since May. This is the first month in 2015 that has been more than 1C below average. Will that trend continue through the rest of Autumn?
Please post your October CET predictions in this thread. The deadline for entries without incurring any penalty is extended this month to 23:59 on Friday evening (2nd) due to this thread being opened late.
October historic data summary
Here is the usual rundown of historic data for previous years.
The last two Octobers have been very mild with a CET of 12.5C. 2011 was similarly mild has have most years been since 2001. But we have had a few cool Octobers as well such as 2008 and 2012 with 9.7C and 2003 with 9.2C. The mean October CET for the last 20 years is a very mild 11.3C.
Long run averages:
1971-2000: 10.4C
1981-2010: 10.7C
1995-2014: 11.3C
Here is a chart of the October CET since 1961 with a 10 year moving average
Current model output
GEFS
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
Above average start but cooler later. This may not translate accurately to the surface though in the first few days as we remain under high pressure.
ECM (DE Bilt)
Sorry my ECM links have broken and I don't have time to sort them at the moment.
Met Office Contingency planners forecast
http://www.metoffice.gov.uk/media/pdf/r/r/A3_plots-temp-OND_v1.pdf
Looks like the probabilities are favouring a warmer than average October which is consistent with the pattern matching analysis below. Strong QBO at the moment also helps to favour a positive NAO although this is likely to be tempered somewhat by the cool Atlantic SSTs. So this reduces the likelihood of a very warm October.
Pattern matching (just for fun)
I have been looking at years where the CET for July, August and September was cool in all three months. I will post something separately in due course about what this might mean for winter but there are very few matches in recent years. However, if you go back to the 1950's, 60's and early 70's you find quite a lot of matches.
Of the 11 reasonable matches I found since 1950 there is not much of a trend as far as the October CET is concerned. But there is tendency towards somewhat milder than average conditions. 8 of the 11 years saw the October CET at or above the 1971-2000 mean with 4 registering 11C or more. But only 1 year was higher than 11.1C (being 1954 with 11.9C). So there are no matches with a CET similar to the 12.5C we saw in 2013 and 2014. There are 3 years with very cool October CETs - 1950 with 9.6C, 1974 with 7.8C and 1993 with 8.5C. So a chance of a cold October but more likely to be close to or slightly above average based on the pattern matching.
October CET tracker
Here are the current prediction charts for the first part of October. After a chilly start it could turn very mild for a time (but more unsettled). If this does happen it will be due to some extremely high minimums rather than maximums increasing. So overall the first half of October could turn out to be rather mild.
Edited by moderator
13 November 2015 10:51:27
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