Well I hope everyone made the most of the reasonably warm conditions this week, at least here in the south. Although the wind did temper that a bit. A major change has taken place overnight in the airmass that is affecting the CET area. We are in a much cooler regime now and will stay that way for the rest of the month. The warm dew points will briefly return to the far south on Sunday as the next major Atlantic low moves across, but you won't really notice that due to the wind and rain.
A substantial fall is expected in the CET for the final 10 days of the month with every day being below average. Indeed Monday and Tuesday look like returning a single figure CET mean. Grass frost will be widespread next week across the UK with air frost likely over the highest ground in the north and in frost hollows. The flip side of that is their will lots of dry, sunny weather with relatively light winds. So it should feel fairly pleasant by day even though temperatures will be lower than of late.
The CET is now expected to finish at 13.70C which is in line with the 1971-2000 mean and quite a bit below the 1981-2010 mean. So the first cool month for a while.
The current CET estimate for the final 10 days of September is 10.90C. That is not especially cold but is much cooler than we have typically seen in recent years. The 1981-2010 mean for the final 10 days is 13.13C. So if the current estimates verify it would be 2.23C below average.
The last time we had such a cold end to September was actually only a few years ago in 2012 when the CET was 10.82C.
It is worth looking at some analogues here. A cold finish to September has often been the prelude to a cool / cold Autumn and some cold weather in the winter.
2012 late Sept CET 10.82C. Oct was cold, Nov and Dec average and then Jan-May 2013 was a very cold period with of course the infamous March.
1993 late Sept CET 10.71C. Oct and Nov were both cold as was the following February. Dec average and January mild.
1974 late Sep CET 9.41C. Oct was also very cold but Nov was average and then Dec and Jan were very mild. But March turned cold again.
1954 late Sep CET 10.62C. Oct and Dec were very mild. But Jan to Mar was a very cold period.
1952 late Sep CET 10.61C. Oct - Dec was a very cold period. Jan also cold and March also below average
1943 late Sep CET 10.40C. Dec was cold but otherwise no significant cold weather followed Sept.
1940 late Sep CET 10.49C. The following Dec through to May was an extended period of very cold weather.
1932 late Sep CET 9.64C. October was cold as was January but otherwise fairly average
1931 late Sep CET 10.83C. Feb was cool but no other month
1928 late Sep CET 9.45C. Dec-Feb was a very cold winter. CET never got above 2.1C in any of those winter months
1927 late Sep CET 10.40C. Cold Dec was the only notable cold month.
1926 late Sep CET 10.38C. No significant cold weather.
I could keep going as there were quite a lot of years with cold ends to September in the early 1900s. Although not so many of these were followed by significant cold periods.
Worth also noting that none of the years above had a hot summer. The warmest summer of any of these years was 15.7C which is bang on the 1971-2000 average. So we have not had a hot summer followed by a cold end to September in the last 100 years.
Might be worth Gavin P doing some analogues of cold ends to September as part of his winter updates series.
Edited by user
21 September 2018 09:23:56
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