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September 2021


Luke Bowett
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Posted
  • Location: Stockport
  • Location: Stockport

    So I haven't looked at the CET in a while but when I clicked on it, my jaw dropped. As of the 17th, the CET is 17.3°! 1.5 degrees warmer than August and 0.5 degrees warmer than the record set in '06. Global warming has proven that August and September have flipped around.

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    Posted
  • Location: Scunthorpe
  • Location: Scunthorpe

    Could be quite possible that starts ticking upwards again this weekend if the predicted warm to very warm spell comes off. Wonder if we could end up with a September CET above the July one this year.

    July came in at 17.7C

    Provisional September value up to the 19th is 17.2C (+3.2C above average)

    I think September 2006's record of 16.8C is a goner now with how many days of the month are left and the warm spell this weekend that should keep us above 17C

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    Posted
  • Location: Exeter
  • Weather Preferences: Warm and sunny!
  • Location: Exeter
    4 hours ago, SqueakheartLW said:

    Could be quite possible that starts ticking upwards again this weekend if the predicted warm to very warm spell comes off. Wonder if we could end up with a September CET above the July one this year.

    July came in at 17.7C

    Provisional September value up to the 19th is 17.2C (+3.2C above average)

    I think September 2006's record of 16.8C is a goner now with how many days of the month are left and the warm spell this weekend that should keep us above 17C

    I have a feeling the usual monthly corrections may just keep 2006 in the lead (although it'll be close).

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    Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

    I think it's unlikely that we'll beat 2006.  In the final third of September you need a bigger temperature anomaly in order to keep the CET that high than you would early in the month - we'd probably need a positive anomaly of 3.5 to 4C in the last third of September to manage it.  Also, as the latest GFS run illustrates, if we had a day or two of polar maritime north-westerlies at the end of the month, that would chop a fair amount off the CET value.

    I reckon we'll probably be looking at something between 16.0 and 16.5 after corrections.  Still pretty exceptional though.

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    Posted
  • Location: Manchester
  • Weather Preferences: Winter: Ice days, clear skies, blizzards. Summer: cool and dry
  • Location: Manchester

    If we had an end similar to September 2011, then I'd say we would beat the 16.8c record. But it is cooling down around the 27th so with corrections I feel like it will sit close to 16c

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.
    6 minutes ago, karyo said:

    Warm Septembers tend to be followed by mild winters so not what I wanted to see.

    To be fair though, @karyo, most Septembers (whether they be cold, warm or indifferent) tend to be followed by mild winters?

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.
    54 minutes ago, Weather-history said:

    Sept 2014: 15.1  Winter 2014-15: 4.5

    Sept 2015: 12.6 Winter  2015-16: 6.7

     

    Well, I did say 'most', Mr. D!

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    Posted
  • Location: Ossett, West Yorkshire
  • Location: Ossett, West Yorkshire
    2 hours ago, Weather-history said:

    Sept 2014: 15.1  Winter 2014-15: 4.5

    Sept 2015: 12.6 Winter  2015-16: 6.7

     

    I have never thought that there is a link between cool or average Septembers and the sort of winter that follows - I really think that the September trend tends to work only at the warm end, that it is a well known fact of the UK's weather patterns that it is very rare to get a cold winter after a really warm September and most of the time winters following warm Septembers are mild.  The example you post about the warm Sep 2014 actually led to a winter that was in fact not that cold, it was still average or even a touch above, despite a very negative QBO as well, of which appeared to give a good chance of it being a colder winter but it wasn't.  After a warm September I would say the result is that they are mostly followed by mild winters, with a small chance that the following winter will be near average, but there appears to be virtually no chance of a colder than average winter after a warm September.

    That said, we have had cold winters after Septembers that were slightly above average but not extraordinarily so, like 1978 and 2009 (in the low 14s), but the warmest that September has been that I can think of, that has led to a winter with at least notable cold spells, is something like 1981 and 1985 (around 14.5-14.6); but I cannot think of any good cold winters following Septembers warmer than this.  

    The overall statistics really show that there is not much of a trend to the type of winters that follow cool or average Septembers, but when September is significantly above average (warmer than about the mid 14s CET), it appears to be very rare to get a cold winter after it.

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    Posted
  • Location: Islington
  • Weather Preferences: Freezing cold snowy winters & unsettled summers.
  • Location: Islington

    I really don't believe that something as arbitrary as temperature in September is indicative of what's coming in the winter. I would be much more inclined to look at synoptic matches, solar cycles, etc.

     

    However, here is a list of warm 15+ Septembers with cold winters following:

     

    1677/1678

    1708/1709 (exceptionally cold)

    1730/1731

    1750/1751 (cold February)

    1779/1780 (sub-zero January)

    1780/1781

    1825/1826 (very cold January)

    1958/1959 (cold January)

    1961/1962 (cold December and bitter early January)

    2005/2006 (while not a bitterly cold winter it was often seasonably chilly and frosty with no overly mild weather and then a cold March)

     

    So, you can see it does happen, and that's why I think it's pointless worrying about it.

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    Posted
  • Location: Carmarthenshire
  • Location: Carmarthenshire

    A quick and dirty comparison of September vs following winter CET from 1760 to 2015 (because Excel will only allow 255 entries on the chart) shows the relationship is all rather random aside from the few very warmest Septembers > 15.7 showing the following winters to be above 5C - probably not enough examples for a meaningful comparison as yet.  

    image.thumb.png.97c2f2fd69fedf90f285c10b815a90ce.png

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    Posted
  • Location: Ossett, West Yorkshire
  • Location: Ossett, West Yorkshire
    1 hour ago, LetItSnow! said:

    I really don't believe that something as arbitrary as temperature in September is indicative of what's coming in the winter. I would be much more inclined to look at synoptic matches, solar cycles, etc.

     

    However, here is a list of warm 15+ Septembers with cold winters following:

     

    1677/1678

    1708/1709 (exceptionally cold)

    1730/1731

    1750/1751 (cold February)

    1779/1780 (sub-zero January)

    1780/1781

    1825/1826 (very cold January)

    1958/1959 (cold January)

    1961/1962 (cold December and bitter early January)

    2005/2006 (while not a bitterly cold winter it was often seasonably chilly and frosty with no overly mild weather and then a cold March)

     

    So, you can see it does happen, and that's why I think it's pointless worrying about it.

    Winter 2005-06 was actually close to average overall - it did have a fair amount of blocking to the north-east, and eastern Europe did see some very cold spells, but the really cold air never succeeded in becoming established over the UK, so for us in the UK, the blocking was mostly a bit too far east and we were left in mostly benign and near average conditions.  As I said, the QBO was easterly that year with a weak La Nina, and we still did not end up with a particularly cold winter.  You rightly point out that further back mostly 200+ years ago there were some Septembers that were warm that did see good cold spells in the winter, but it seems at least in the modern day, and since back into the 1800s, the trend is clear that it is very rare to get a cold winter after a significantly above average September.  It seems as though the September / winter relationship only works with the warm September reducing the chances of cold weather in the following winter, whereas if September is average or cool it is not clear that there is any trend in the sort of winter that follows.  The warm September relationship in ruining the chances of the following winter being cold, I would say has got to be one of the most well known aspects of the UK's weather patterns.

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