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November CET: recent history of trends - mid month - month end


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Posted
  • Location: Steeton, W Yorks, 270m ASL
  • Location: Steeton, W Yorks, 270m ASL

    As for September, here's the November history (since 1975). I've projected a band of 8-9C by the 15th. That would be slightly lower than recent years, bar 2006 - when the outcome finished higher (around 8.1C).

    Intriguingly, from this presumed point, historic outcomes have polarised. The majority finish 8.0C or higher; big falls tending to be in instances where the mid point was unusually warm. There's also a significant minority that cool markedly, into the 6-7 range. Anything lower would be without equal in this sample.

    Tough call from here: it could go cool later in the month, as GP and others show, with a Nina it can be shown that there's a decent relatiinship. Looking at BF's reanalyses, I just wonder whether we aren't missing the slight poleward shift of the PF, and I suspect that we might end up with 'bad luck' synoptics; some cool air, but the coldest sustained air often missing either to our E, or being held just north by HP to our SW.

    I'd also expect a more dynamic pattern towards the month end, which would also argue against sustained cold. At this distance, 7-8 would be my very provisional wet finger.

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    Posted
  • Location: Tunbridge Wells, Kent
  • Location: Tunbridge Wells, Kent

    Interesting

    Not suprised only 6 out of 32 warmed from mid month as the graph is still pointing south although flattening rapidly toward the end of the month.

    2005 was a clear outlier, but it does demonstrate that the downside potential is massive as 0C days are easily possible in November.

    If your CET is sat at 10C mid month and a potent northerly pops up then you can be down to 7.5C in 4 days

    2005 events aren't obviously that common however a couple of similar scenarios have come up of the models of late

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    Posted
  • Location: Steeton, W Yorks, 270m ASL
  • Location: Steeton, W Yorks, 270m ASL
    Interesting

    Not suprised only 6 out of 32 warmed from mid month as the graph is still pointing south although flattening rapidly toward the end of the month.

    2005 was a clear outlier, but it does demonstrate that the downside potential is massive as 0C days are easily possible in November.

    If your CET is sat at 10C mid month and a potent northerly pops up then you can be down to 7.5C in 4 days

    2005 events aren't obviously that common however a couple of similar scenarios have come up of the models of late

    Certainly H2 warming is more likely in November than in Sept / Oct, and cold can be potent - though rarely the case nowadays. I think at any time, though, a drop of 2.5C in four days would be unlikely; that would actually require a net negative return across the period of around -2C per day: that's a huge ask in mid November. In fact, it's a huge ask at pretty much any time nowadays.

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    Posted
  • Location: Tunbridge Wells, Kent
  • Location: Tunbridge Wells, Kent
    Certainly H2 warming is more likely in November than in Sept / Oct, and cold can be potent - though rarely the case nowadays. I think at any time, though, a drop of 2.5C in four days would be unlikely; that would actually require a net negative return across the period of around -2C per day: that's a huge ask in mid November. In fact, it's a huge ask at pretty much any time nowadays.

    Perhaps my example was a little extreme however 0.5C, 0.6C or possibly 0.7C movement in a single day mid month is possible in November if starting from a higher than average base.

    I would suggest that only April if it had a cold/cool start and then a mid month heatwave could replicate in reverse and possibly May and October. Cant see any other months having that much upside or downside potential once a half months worth of data is on the table.

    Nothing significant in this however, just interesting from my point of view.

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    Posted
  • Location: Steeton, W Yorks, 270m ASL
  • Location: Steeton, W Yorks, 270m ASL
    Perhaps my example was a little extreme however 0.5C, 0.6C or possibly 0.7C movement in a single day mid month is possible in November if starting from a higher than average base.

    I would suggest that only April if it had a cold/cool start and then a mid month heatwave could replicate in reverse and possibly May and October. Cant see any other months having that much upside or downside potential once a half months worth of data is on the table.

    Nothing significant in this however, just interesting from my point of view.

    I think that's more sensible Stu, but even then, to register 0.5C would require an outturn at 7.5C below running mean. As you say, it would require either unusual mild period to date, exceptional cold on the day concerned, or some combination of the two. What has then to be remembered though is that subsequent falls will be significantly moderated, all other things remaining equal.

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