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The coldest/hottest you could possibly get in a calendar month.


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Posted
  • Location: Islington
  • Weather Preferences: Below zero and preferably a bunch of snow! Cool summers.
  • Location: Islington

    An interesting, if not rather unanswerable question. It came to me when looking at synoptic charts from the past and wondering the type of months you would get if the same pressure patterns/anomalies presented themselves in the opposite season. I was looking at a February with frequent winds from the north and east and it made me wonder, "what is the coldest C.E.T. you could possibily achieve in a summer month?", but also it would be interesting to ponder the hottest or mildest.

    For many years, the idea of a December in the 9s would have been ridiculous, but then December 2015 smashed it. In a less extreme manner, there was no July in the 19s until July 1983, a figure perhaps thought of as unachievable, especially after a couple decades of cold, soggy summers.

    If a summer month were to be completely dominated by northerly sourced air, how cold could it possibly get? August 1912 is perhaps the closest example we have in detailed record to this kind of month in summer form, on the cold side - being the coldest, wettest and dullest August on record. A look through the synoptics though does show the odd day with a southerly incursion, even if extremely fleeting. Without this, would it be possible to get an August in the 11s or below? Same with July in the 12s, June in the 10s etc. 

    On the flip side, we know a 31 day period can average 20C as it happened in 1976 and 1995, but what about 21C?

    The short answer is obviously yes. A changing climate, whether colder than we currently know or warmer, will obviously change the scope of what is possible, but I am referencing the climatological norms of the past 300 years or so, though that is seemingly changing before our eyes...

    Months like December 2015 and May 1833 are so interesting because they challenge our perceptions of what is possible in the record books. 

    Any thoughts and ideas are highly looked forward to!

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    Posted
  • Location: Manchester
  • Location: Manchester

    You'd think December 2015 would be the upper limit of what's possible for December- it's hard to imagine how it could possibly be any milder unless the UK moved a few hundred miles further south. Temperatures were consistently in the 13-16C range throughout the month- hard to see how it could get higher than that consistently. The cloud cover also kept temperatures in double figures on many nights- again hard to see how it could be milder.

    It's feasible that we could get an equivalent January or February but less likely due to cooler SSTs as the season progresses.

    I think April to September are the months that could theoretically go a lot higher than anything we've seen due to the longer days and stronger sun in those months.

    I've always thought it strange that no other month has challenged May 1833. All we would need is a very blocked month with high pressure stuck to our east and a flow off the continent. The only thing stopping May being as warm as the summer months is the seasonal lag and this would be negated a great deal with a consistent continental flow throughout the month which is theoretically possible, although the odds are always against it. 

    Other than SSTs, everything else is there in May- increasingly long days and strong sun.

    June is the other one that could go a lot higher in theory- get the right blocked setup with a continental flow throughout the month and 1976 could easily be smashed. Don't forget that the first half of June 1976 was nothing to write home about. Imagine if there had been another hot spell (less hot) earlier in the month as well.

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    Posted
  • Location: Exeter
  • Weather Preferences: Warm and sunny!
  • Location: Exeter

    I think September could get into the 17s, maybe even scrape 18°C.  I don't see why a 14°C October might not be possible in the future.

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    Posted
  • Location: Longden, Shropshire
  • Location: Longden, Shropshire
    3 hours ago, Earthshine said:

    I think September could get into the 17s, maybe even scrape 18°C.  I don't see why a 14°C October might not be possible in the future.

    I think there was a point during September 2021 when it looked as though it could finish around 17C, but a late cool down prevented it.  I'm sure a 14C October will be possible in future if climate change continues to accelerate as it is doing!

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    Posted
  • Location: Liphook
  • Location: Liphook

    May and June really do stand out on the CET rankings. Most months have at least a few representatives from post 2000 in the top 10 but they are totally missing in May and June. June for example you have to wait till you get to 23rd place to find a year from 2000 in the list (2018).

    May 1833 really must have been an amazing record back then and we've not really even come close in recent years.

    The one big one I'm watching is the first 20.0c month. July 2006 came pretty close and we've had occasional 30 day means go above that level, but its clearly still in the exceptionally rare bracket (IE, theortically do able, but right at the limits.)

    Mind you, 40c would have been in that same bracket about 6 months ago!

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    Posted
  • Location: Rossland BC Canada
  • Location: Rossland BC Canada

    Part of the answer is to ignore the rigour of the calendar, there's no reason why the warmest 31-day interval (now about 20.2) couldn't overlap calendar months July or August. I think sooner or later there will be a 20.5 to 21.0 month (at least ignoring the calendar), that might be about the upper limit but who knows in a warming climate? 

    Same comments apply to winter, Dec 2015 probably did max out its potential without needing help from either end of nearby months, so 10.0 may be the absolute limit for December and possibly 9.0 for Jan and Feb. The warmest March (1957) will perhaps be one of the earlier ones to go (9.2), May could hold on for a long, long time but the interesting thing is that May 1833 had reached a running mean of 15.6 around the 24th before losing a bit near the end. June (18.2 in 1846) will likely fall in this century despite the noted lack of very warm Junes in recent decades. 

    As to different synoptics applied to other parts of the year, they just wouldn't occur in nature so it's difficult to know, like a 1050 mb high stagnant over Scandinavia in July would no doubt just be like a 1030 mb high, I believe, the temperatures associated might not be any different because of the short duration of overnight hours. A Daniel Defoe type storm moving in during high summer would no doubt be an overperforming Atlantic hurricane that happened to wander far afield. The temperatures and dew points with it would likely be something like 23/21 as they would be responding to recent ocean passage (over a very warm ocean). It's no doubt going to happen sooner or later, warming climate or not, that a mature not quite extratropical hurricane will move into the region, it already has to some extent with Debbie and Ophelia (Charley was more about rainfall). 

    Climate extremes can sometimes be quantum leaps, who would have suspected we would jump from 25.3 to 28.1 as warmest CET daily mean? Before that leap, the 25.3 (2019) which had been 25.2 in legacy CET, and had merely tied the existing mark from 1948, was no great advance, and the 1948 high point was (from memory here) 0.7 higher than a value from 1808. Daily values don't go back far enough (1772) to judge how big a jump that was (perhaps a degree). 

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    Posted
  • Location: Irlam
  • Location: Irlam
    On 01/11/2022 at 16:37, LetItSnow! said:

     

    For many years, the idea of a December in the 9s would have been ridiculous, but then December 2015 smashed it. In a less extreme manner, there was no July in the 19s until July 1983, a figure perhaps thought of as unachievable, especially after a couple decades of cold, soggy summers.

     

    The other side of the coin was December 2010, I don't think anyone expected that the next subzero CET month  (some were even question whether this could still be achieved) would be a December but the amazing thing is that wasn't even the extreme  as 27th November-27th December recorded a CET of -1.6°C    The coldest 31 day CET period for the the second half of the year since at least 1772.

     

     

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

    I reckon June 1975 will take some beating: from widespread frost/snowfall on the 2nd to 30C+ by the 6th!🤔

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    Posted
  • Location: Manchester
  • Weather Preferences: Winter: Ice days, clear skies, blizzards. Summer: cool and dry
  • Location: Manchester
    14 minutes ago, Weather-history said:

    The other side of the coin was December 2010, I don't think anyone expected that the next subzero CET month  (some were even question whether this could still be achieved) would be a December but the amazing thing is that wasn't even the extreme  as 27th November-27th December recorded a CET of -1.6°C    The coldest 31 day CET period for the the second half of the year since at least 1772.

     

     

    I wonder if we will ever get a winter month as extraordinary as December 2010. -0.1C away from the all time record of -0.8 in 1890, that's crazy.  2015 was impressive but on the other end of the spectrum

    I wish to relive 2010 again, some amazing weather for coldies that year. 

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    Posted
  • Location: st albans
  • Location: st albans
    26 minutes ago, Frigid said:

    I wonder if we will ever get a winter month as extraordinary as December 2010. -0.1C away from the all time record of -0.8 in 1890, that's crazy.  2015 was impressive but on the other end of the spectrum

    I wish to relive 2010 again, some amazing weather for coldies that year. 

    Can we wait until the energy crisis is over ? 

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    Posted
  • Location: Islington
  • Weather Preferences: Below zero and preferably a bunch of snow! Cool summers.
  • Location: Islington
    On 04/11/2022 at 00:02, Roger J Smith said:

    Part of the answer is to ignore the rigour of the calendar, there's no reason why the warmest 31-day interval (now about 20.2) couldn't overlap calendar months July or August. I think sooner or later there will be a 20.5 to 21.0 month (at least ignoring the calendar), that might be about the upper limit but who knows in a warming climate? 

    Same comments apply to winter, Dec 2015 probably did max out its potential without needing help from either end of nearby months, so 10.0 may be the absolute limit for December and possibly 9.0 for Jan and Feb. The warmest March (1957) will perhaps be one of the earlier ones to go (9.2), May could hold on for a long, long time but the interesting thing is that May 1833 had reached a running mean of 15.6 around the 24th before losing a bit near the end. June (18.2 in 1846) will likely fall in this century despite the noted lack of very warm Junes in recent decades. 

    As to different synoptics applied to other parts of the year, they just wouldn't occur in nature so it's difficult to know, like a 1050 mb high stagnant over Scandinavia in July would no doubt just be like a 1030 mb high, I believe, the temperatures associated might not be any different because of the short duration of overnight hours. A Daniel Defoe type storm moving in during high summer would no doubt be an overperforming Atlantic hurricane that happened to wander far afield. The temperatures and dew points with it would likely be something like 23/21 as they would be responding to recent ocean passage (over a very warm ocean). It's no doubt going to happen sooner or later, warming climate or not, that a mature not quite extratropical hurricane will move into the region, it already has to some extent with Debbie and Ophelia (Charley was more about rainfall). 

    Climate extremes can sometimes be quantum leaps, who would have suspected we would jump from 25.3 to 28.1 as warmest CET daily mean? Before that leap, the 25.3 (2019) which had been 25.2 in legacy CET, and had merely tied the existing mark from 1948, was no great advance, and the 1948 high point was (from memory here) 0.7 higher than a value from 1808. Daily values don't go back far enough (1772) to judge how big a jump that was (perhaps a degree). 

    Interesting. Thank you.

    Though when I spoke about the opposite synoptics, I meant far less the exact same and more if the same anomalies from years past were to occur in the opposite months of the year. Like, for example, if the general pattern of February 1986 (strong block = frequent easterlies) were to occur in August, it would probably bring a very hot month. Same how many a poor summer month's synoptic anomaly flipped to D/J/F probably would bring a mild, stormy month.

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    Posted
  • Location: Maidstone, Kent
  • Weather Preferences: Anything below 0c or above 20c. Also love a good thunderstorm!
  • Location: Maidstone, Kent
    On 05/11/2022 at 11:02, Frigid said:

    I wonder if we will ever get a winter month as extraordinary as December 2010. -0.1C away from the all time record of -0.8 in 1890, that's crazy.  2015 was impressive but on the other end of the spectrum

    I wish to relive 2010 again, some amazing weather for coldies that year. 

    Obviously one can never say never but I feel we have maxxed out on December at least for the rest of this century. Interesting how in the space of 5 years we've experienced both how cold a December can get and how warm it can get. I'm not yet 30 but I reckon even for people like me Decembers will never beat those two months for their extreme nature, they'll always be 'nah not like 2010' or 'nah not like 2015'.

    I'll definitely return to this thread again soon once I've looked at some stats. A very interesting thread!

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    Posted
  • Location: Rossland BC Canada
  • Location: Rossland BC Canada

    All the discussion of warming climate has pushed natural variability to the background but it is still operating and you have to wonder with the evident new wild card of human influence in the deck, what can the atmosphere do in the future that it has not done in the recent past? We don't really know for sure whether a warming climate would see both ends of the spectrum warming (so never as cold as in the past) or greater variability which could permit the lower end to remain static or even drop slightly while the top end of the range continues to increase. 

    December 2010 may not be a "one off" event in that scenario, perhaps as anomalous warmth sometimes takes up residence in blocking patterns well to the north, that sort of prolonged record cold will return in other winters. We have seen three other notable cold spells but some were briefer, or less intense, with Mar 2013 (into early Apr), then late Feb to early Mar 2018 and April 2021. 

    The UK climate does not seem to do cold Februaries any more, but I feel that's a statistical quirk waiting to be extinguished, given that March 2013 was a very cold month also, no reason why a February cannot be as anomalously cold which would likely produce a mean near 0.5 nowadays. A pattern like March 2013 in February would probably produce a lot more snow than Mar 2013 also.

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    Posted
  • Location: Longden, Shropshire
  • Location: Longden, Shropshire
    12 minutes ago, Earthshine said:

    I think we'll see a 17°C+ June this decade.

    We have not an exceptionally hot June for many years, so we must be due one?!

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

    The May CET of 15.1C has to be broken at some point..dont think it'll be this decade but I think we will see a 14C May at least. 

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    Posted
  • Location: halifax 125m
  • Weather Preferences: extremes the unusual and interesting facts
  • Location: halifax 125m
    On 05/11/2022 at 11:02, Frigid said:

    I wonder if we will ever get a winter month as extraordinary as December 2010. -0.1C away from the all time record of -0.8 in 1890, that's crazy.  2015 was impressive but on the other end of the spectrum

    I wish to relive 2010 again, some amazing weather for coldies that year. 

    The Manchester winter index puts December 2010 at -0.7 deg yet here just a stones throw away December 1981 was -1 deg.There is no doubt however that we will experiance another subzero month it was a long gap between 1986 and 2010 but we have had 12 years since the last one already.Maybe not as long to wait as you might think .

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    Posted
  • Location: Longden, Shropshire
  • Location: Longden, Shropshire
    4 hours ago, hillbilly said:

    Maybe not as long to wait as you might think .

    With climate change gathering apace though, surely it will make a sub zero month more and more unlikely as the years tick by.

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    Posted
  • Location: Hampshire
  • Weather Preferences: Bright weather. Warm sunny thundery summers, short cold winters.
  • Location: Hampshire

    I would say the theoretical maximum for each month might be, about:

    January 18C

    February 21C

    March 26C

    April 30C

    May 35C

    June 38C

    July 40C

    August 39C

    September 35C

    October 30C

    November 21C

    December 17C

    Some of these have been reached as we've seen, but not all (see March, April, May, June, August and I think September). The spring and early summer in particular seems to have lacked really extreme warmth/heat of the sort seen in mid-summer and autumn.

    Edited by Summer8906
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