North-Easterly Blast

@sundog Looking at records, it is a well known fact of the British weather patterns that anomalous warmth in September (a high September CET) bodes badly for cold conditions during the following winter, in particular from high latitude blocking and northerly and easterly spells. I have looked at Septembers over previous years and my conclusion is that a cooler or even average September CET appears to have very little bearing on the following winter's weather patterns, and it looks to be still possible in some cases to have a near or even slightly above average September CET and still have a colder winter to follow, but it is very rare, if not almost unheard of, to get a cold winter in the UK, or to get a winter that is anything other than above average, after anomalous September warmth in terms of a high CET. It is clear that if you are hoping for a reasonable chance of cold outbreaks in the winter to follow, you do not want to see anomalous warmth in September like last year, and a number of others in the last 25 years or so.

Yes very true, although there were two notably mild Januarys in 2007 and 2008.

Another January passes by without being notably cold. Only January 2010 was significantly (well) below average since 1987. In fact we have had no January other than 2010 with a CET under 2.5 in the last 37 years. In recent times we have on odd occasions been a little under the older historical 1961-90 (and even 1951-80) average, in 2021 and 2013, but other than 2010, we have not had another January that could reasonably be described as "significantly cold" since 1987, so the lack of really cold January CETs in the last 37 years must be close to, if not a record.

Well as for anyone saying that UK winters are getting colder, the truth is, and you cannot hide the facts, that we have not had a below average winter since 2012-13 (by 1961-90 standards) in terms of the overall CET - that is now over ten years ago. We have also not had an overall really cold winter since 2009-10 - 14 years ago, and we have not had a single notably cold month since December 2010 (13 years ago), though that said if you count it as winter the last single notably cold month that we had was March 2013. Putting the above into perspective, all this evidence points against winters in the UK getting colder. No winter in the UK since 2012-13 could reasonably be described as being colder than average, and since then winters 2017-18 and 2020-21 were respectable for the standards of the last 35 years or so, but still slightly above the 1961-90 and most earlier averages. Most winters since 2012-13 in the UK have been milder than average with little in the way of cold outbreaks (at least from HLB and notherlies / easterlies) and a fair few in the very mild category.

You are dead right there. I cannot think of a year from memory in the last 30 odd years that had a notable warm / hot spell in late August (around the last week of the month), despite a number of years in that time having a notable warm spell in the first week or so of September. Even August 1995's heat fizzled out in the last week of the month, as did August 1997, and August 2003 became cool in the final week of the month. We seem to have had so many early September warm spells, but we do not seem to be able to achieve a warm spell in the final week of August.

I think that before 1986, the previous time that we had such a cool August was 30 years before it in 1956, which overall was a wetter month than in 1986. There were similarly cool Augusts further back in 1920 and 1922, and of course, the coolest on record in 1912. If you look at rainfall for August 1986, the overall EWP average is 118mm, which is similar to that of August 2020 which was 3.9*C warmer for the CET, so although August 1986 was very cool, it would have felt similar rainfall-wise to the warm August of 2020. Another example is that August 2004's rainfall of 156mm combined with a CET of 17.6 was only 2mm drier than August 1956 that was over 4*C cooler for the CET. September 1986 was certainly very cool with a CET of 11.3, although this was a dry month dominated by high pressure to the north of the UK which allowed cool airstreams from the north to cover the country producing a large number of cool nights and even occasional frosts, but the average maximum CET in Sep 1986 was similar to that of Sep 1993, so it was the cool nights in Sep 1986 made the overall CET over a degree lower than that for 1993. Just for the fun of it, it would be interesting to see an August like 1986 again, although the coolest August that we have had in recent times was in 2014 which had a CET of 14.9 on the legacy series, but slightly higher on the revised series.

Looking at average CETs for July, on the legacy series; the 1961-90 average is 16.1*C (16.05), and the 1991-2020 average is 16.8*C (16.79). In between those the 1971-2000 average is 16.5*C (16.48) and the 1981-2010 average is 16.7*C (16.71). Looking at this we did have some fairly cool Julys in 2011 and 2012, and the coolest since then was in 2020, which did finish slightly below the 1961-90 average.

I think that I was referring more to topsy turvy months that had spells of both above average and below average temperatures, or spells of two or more different weather types in them. You are correct that it is less common to get the coldest February weather later in the month compared to earlier on, but another of those examples for February that I can think of is 1994; now that was a fairly cold month but with the cold spell centered on the middle to latter half. Another February as well that I can think of that was cold in the second half compared to the first half was 1981.

Months of two halves that I can think of: February 2005 had a colder second half compared to its first half. August 2020, a hot first half followed by a very wet second half and cooler compared to its first half. Februarys 2009, 2012, and 2021 all had cold first halves then went downhill into very mild second halves. June 2005 was a bit of a reverse of 2004; that had a relatively cool first half then a warm second half. February 2019 wasn't particularly cold in the first half, it was only cold for the first three days, then it turned milder with some unsettled weather before becoming exceptionally mild and settled in the second half, although I should say warm, as the second half of that month was more typical of an April spell of weather than February. November 2005 - a mild first half then a cold second half. In some ways November 2010 was of extremes - that started very mild then became average, and exceptionally cold in the last week.

Well the most notable feature is that we are long overdue a notably cold February. We have not had a really cold one since 1991 - 32 years ago. We have not had a winter that was even below average at all by 1961-90 standards since 2012-13, so there has been far fewer cold outbreaks since then - so it can be said that many different parts of the winter season have lacked notable cold spells since then.

The 1961-90 winter average is 4.1*C, and if you go back to the 1951-80, then the winter CET average is 4.0. Going further back to 1941-70, then the winter CET average is 3.8. So 2012-13 was just about a typical 1941-70 winter, although it had a notably cold March on top.

March 2013 had a CET of 2.7 on legacy, but Cv2 revised it upwards to 2.8. January 2013 is one of those months where the overall CET does not tell you accurately about the sort of weather that the UK experienced during the month. It contained a two week significant cold spell from the 10th to 25th where the CET was -0.1 for 16 days, but the CET up to the 8th was 8.0, so it had a very mild first eight days, and then it turned milder late on in the month, so it was a case of where despite it having a 16 day significant cold spell, the month's overall CET actually didn't end up particularly cold in the end. February 2013 was one of those months that was generally cold for most of the month, with little in the way of mild weather, but did not really have a big freeze.

Mid January to mid February 2002 had a CET of 8.0, which is higher the all time record for each of the calendar months of January and February. I believe that December 2001 was one of those cool but nothing exciting months - in that it was anticyclonic with frequent frosts but without any real major cold spells - just short lived northerly outbreaks later in the month, although it did become cold in the final few days and this lasted into the opening days of January 2002, before it all went downhill significantly and there was no further cold weather at all for the rest of the winter.

Februarys 2013 and 2018 were below the 1961-90 average as well. February 2015 was in between the 1961-90 and 1971-2000 averages. It is certainly a true nail in the coffin for cold to think that since the CET record began in 1659, there were about 45 Februarys that had a CET of 6*C and above, but five of those were in the last ten years. Just over ten years ago, 2011 also saw a very mild February as well (6.4 on legacy, 6.5 revised), so that makes it that six of the 45 6+CET Februarys in the CET record have been in the last 12 years. Further back, there was a similar run of extremely mild Februarys in the late 1990s to early 2000s, with 1995, 1997, 1998, 2000 and 2002 all having CETs over 6*C, so that means that 11 of the 45 6*C+ Februarys in the CET record have occurred in the last 28 years. All this is just ridiculous and sickening from a cold perspective. Something has certainly gone wrong to cause this. On top of that, we actually went 29 years from 1961 to 1990 without ever seeing a 6*C+ February CET. I know that in the mid Victorian era there was a notably high number of very mild Februarys for a number of years, but I think that the last 30 odd years have had milder Februarys overall than the mild February period of the mid-Victorian era. So again we avoid a cold February. It is now 32 years since we last had a really cold February, in 1991. On a handful of occasions in recent times we have been 0.5 to 1*C below the 1961-90 average, such as in 2010, 2013 and 2018, and way back in 1996 we got down to 2.5 CET, but there has not been a significantly cold February (CET under 2*C) since 1991. (32 years ago). It just makes one ask the question that "Will we ever see a really cold February (CET below 2*C) ever again?" For one possible answer to this, I looked at the weather patterns of earlier in the winters that had really cold (sub 2*C CET) Februarys in the past, and it appears that the majority of really cold Februarys with CETs below 2*C, had been preceded by a significant cold outbreak for a while in the December or January before them, with about the only main exception to this that I can think of being 1982-83, now that winter had a cold February following little in the way of significant cold outbreaks earlier in the winter, but it appears that, if there has not been a cold spell for a while in the preceding December or January it appears that the odds are stacked against getting a cold February.

Yes when the 11 day December cold spell broke on the 18th of that month, the weather abruptly switched to a mild zonal pattern almost non-stop for another four weeks, then we did get just over a week of colder weather (although nothing overly dramatic), but since about January 25th it has just been a complete high pressure borefest, devoid of any cold outbreaks and just a few night frosts here and there. Basically it has been a potent cold spell staring winter off then it disappeared abruptly on December 18th into next to nothing apart from a cold feeling week or so just after mid-January.

In reality so far it has been a winter of a very cold 11 days in December, then a very mild four week spell from December 18th to January 14th, then a colder, but nothing overly dramatic, period for ten days, then from January 25th up until now in the second week of February, an average to mild, anticyclonic, uneventful period, with a few night frosts at times, but never anything that cold by day.

Well the CETs do not really back that up. December 2022 did have a notable cold spell for 11 days but that fizzled out after the 18th, and the month did finish colder than average, although slightly less cold than December 2009. January 2023 was quite a mild month overall, although it did get colder for a time from around mid-month up until about the 24th, and its CET was 3.7*C warmer than January 2010 - so significantly milder. February 2023 has been quite mild so far with its CET up to this point being well into the 5s, though it has had a fair few frosty nights.

Although on average March, particularly the first half, is on long term averages not much different temperature-wise to the start of winter (early and mid December), so all in all, the first half of March often brings a similar amount of cold weather to early and mid December. Whereas when you reach the second half of March average temperatures do on average begin to increase for spring, then on average it gradually gets warmer as time passes through April, May and into June.

I think that there is now a good chance of winter 2022-23 ending up slightly colder than the 1991-2020 average, but being below the 1981-2010 or 1971-2000 average is looking less likely now, let alone being under the 1961-90 average. For something of note, although this winter has not been particularly cold, this February only needs a CET of 4.3 or less to make it the coldest winter since 2012-13. This now looks unlikely although it could be possible if a cold spell does materialize later in the month, but something in the 5s looks favourite for this month at the moment, which would mean that winter 2022-23 would finish a little milder than 2017-18, 2020-21 and likely 2014-15.

When you look at records, it clearly appears that in 1988 that the UK entered a warm era where cold outbreaks in the winter became much less frequent and generally more short lived than prior to 1988, and in the 1988-2013 era, only 1990-91, 1995-96, 2008-09, 2009-10, December 2010, and 2012-13 brought winters that could reasonably be described as being cold, or having notable potent and long lasting cold spells in them, showing that in the 1988-2013 era, it was still possible to occasionally get significant cold spells or a colder winter overall in the UK. Other than that, any cold outbreaks in other winters were mostly less potent and relatively short lived, and many winters in the 1988-2013 period were notable for the lack of cold outbreaks in them. Though since the 2012-13 winter, we appear to have moved into a super warm era, with both the mild winters and the lack of winter cold outbreaks stepping up a gear compared with the 1988-2013 era. I mean to say that before 2013; December 2015 style winter warmth or February 2019 style winter warmth was unheard of, and winters like 2013-14, 2019-20 and 2021-22 that notably lacked any even modestly cold outbreak were almost unheard of prior to 2013. In the last ten years the most "colder winter weather" that the UK has experienced has been relatively short lived potent cold outbreaks, or longer lived rather tame, more moderated cold periods, and it appears that a winter like 2017-18 or 2020-21 (which were a little below the more recent averages but still a little above the older averages) may be regarded as cold or even severe in the post 2013 era and as the new benchmark for a colder winter, and that now and ever since 2013, the sort of cold winters that occurred late in the more modest warm 1988-2013 era, like 2009-10 and 2012-13, and month long lasting severe cold spells like December 2010, may well and truly be now consigned to the history books.

To me and looks and has also been said a number of times that a winter like 2020-21 or 2017-18 may be regarded as cold or even severe in the post 2013 super warm era, and that getting a colder than average winter (by 1961-90 standards) is no longer realistically possible, and that 2017-18 or 2020-21 may be the new benchmark of the greatest depth of cold now realistically possible in a UK winter.

At this stage anything from the 4s to the 6s is possible for the final CET, with something in the 5s looking favourite at the moment, which would still be a milder than average winter by 1981-2010 standards, and winter 2022-23 could still even finish above the 1991-2020 average. This would clearly put into perspective that it looks almost certain that after 2013 the UK entered a "super warm era", and that winters like 2009-10 and 2012-13 and spells like December 2010 are now well and truly consigned to the history books and will never be seen again, and that a winter like 2017-18 or 2020-21 may be regarded as "cold" or even "severe" in the post 2013 super warm era, and the greatest depth of cold that it is now realistically possible to achieve in an UK winter.

The cold spell in January 2013 was quite potent and lasted for two weeks, and that followed an SSW I believe. The late Feb / early March 2018 cold spell was an intense and potent although not particularly long lived cold spell as it was for little more than a week, although it did return for a time in mid March 2018. Further back, late February 2005 saw a great cold synoptical setup develop with a reasonably long lived easterly spell (a fair bit more long lived than the late Feb / early March 2018 easterly) and the cold synoptics lasted into early March, although the weather that the UK experienced on the ground never really quite lived up to its full potential for the synoptics that developed. The synoptics from around Feb 20th to early March 2005 look great on paper to get the cold air in to the UK, but at that time Central Europe was not particularly cold, and so the cold air that reached the UK was moderated somewhat, and although snow fell at times in many parts of the country including to lower levels, any lasting snow cover was mostly restricted to areas with elevation. If central and eastern Europe had have been properly cold at that time, the late February 2005 easterly spell really could have been as potent for cold as the one in late Feb 2018 but more long lived as well. The late February 2005 easterly spell developed after what had been a quite a mild winter up to that point with not much going on from a cold perspective, and showed that it was still possible to get a pattern change late in the winter to something favourable, although I am not sure if there was an SSW shortly before it developed.

I would say that a February CET finish somewhere in the 5s looks favourite at the moment, and yes we could still see a very mild 6s finish if the month remains devoid of anything remotely cold, but if the SSW predicted in a week or so's time helps something colder to materialize before the end of the month then a final CET in the 4s could be possible.

February 1955 sticks out to me as being very similar synoptically to February 1969, and in the type of weather that it delivered. In both Februarys 1955 and 1969 the cold spells were maintained by Greenland Highs and the cold was mostly from northerlies with low pressures at times approaching the UK from the south at times in both months. Prior to the cold February 1955, the cold spell in early to mid January 1955 was brought about by a similar setup especially in mid Jan 1955, but we did get a cold spell from the east with a Scandy High in the early part of Jan 1955. Although Jan 1969 was not up to much in terms of cold, late December 1968 (around Christmas to New Year) saw a cold spell from very similar synoptics to mid January 1955. Following on from 1955, we did have a very cold February again in the following year (1956), although the cold that month came mainly from the east and Scandinavian blocking as opposed to Greenland blocking and the cold from the north.