Longest run of consecutive wet months?

[LetItSnow!]

 Summer8906 I perhaps wonder if this is a symptom of the rising Hadley Cell. Poor summer months in times gone by were usually very cool but weren't always remarked as extremely dull. Due to weaker heights to our south, low pressure often had an easier time pushing straight through or even becoming a cut off low (July 1987) that wandered around for days. That happened a lot, yes, but I suppose it did allow for more PM air which at times was more showery. It could also explain somewhat our less thundery summers as if you look at the reports from the very poorest summers, they often had very severe thunderstorms which made them very interesting. Summers like 1980, 1985, 1987 etc all had severe thundery spells and not always from plumes. I think the more southerly track lead to "different" types of unsettled conditions and also N Atlantic ridges which brought cool but dry spells of weather which are almost non-existent now.

Instead nowadays, with high pressure becoming semi-permanently fixed over Iberia, the areas of low pressure become stuck and often have a TM airmass associated with them, which brings unexceptional days but very mild nights and a whole lot of cloud and oddly, perhaps less thunder. It also means those cool ridges become harder to maintain because the forcing is coming from the south with these heat pulses wafting up.

Short version: Pre-1990s could often be cool, dull and wet, but could have different types of "poor" conditions which were usually brighter and also more convective, but now we have more humid, boring south-westerly conditions due to a semi-permanent southerly quadrant to our summer winds.

Just a thought. It's basically what's happeend to our winters so why not our summers too.

If this needs to be moved elsewhere, .

[Summer8906]

 LetItSnow! I think that probably is the case. Previous poor summers as you say did seem to have more in the way of colder polar airmasses from north of west, and many of the lows moved on a WNW-ESE track. This meant that there was more polar air and it was perhaps brighter. As well as the 80s, the 2007-2011 period seemed a bit like this too: while often very wet these summers didn't have the long periods of damp, drizzly air that have characterised a lot of recent summers.

It also seems to be the case that thundery slack lows in polar air are more rare in the summer, as you say.

A poster in another group referred to the "anomalous northwesterly" in 2007-12 in which the summer wind direction was more NW-ly than usual which brought cool and changeable weather. I also do remember the now-rare cool and dry conditions you mention occasionally occurred in this period: much of August 2007 was dry and on the cool side, parts of June and the middle part of July 2008 the same, and parts of August 2009 and July 2010, as well as the first 10 days or so of July 2011. I remember cool and dry used to be quite a common setup during June - I have quite a few memories of June days with not especially warm daytime temps, days which started and ended sunny with Sc sheets in the midday period, and a strong Atlantic anticyclone. June 2000 had a lot of weather like this if I remember right as well as the first half of June 1995.

Now we seem to have an "anomalous southwesterly" in the summer and the lows still come, but this time on a WSW-ENE track producing cloudier and more humid conditions with mostly Tm and rPm (both often dull) and little true Pm getting a look-in. The second half of August 2020 is a good example of the wetter end of this type, while the first half of August 2021 would be a good example of a less-wet but still dull and damp variant.

Perhaps it's less Iberian high pressure driving this, though, and more high pressure over central and southeastern Europe, hence a SW-ly type across most of Europe which means hot and dry to the south and southeast but dull and damp to the north and northwest. It does seem that the normal NW-SE rainfall gradient across Europe has been exaggerated in recent years with Germany, not too far from here, receiving a lot of droughts and warm to hot summers when it's been dull and damp here.

A lot of our previous poor summers were also poor in central Europe, with the formerly common NW-ly type also associated with extensive shallow low pressure over the continent. For example in July 2011 I spent about 10 days in Austria and Germany and the weather was frequently cool and unsettled. The first half of July 2012 was unsettled in the Austrian Alps, albeit warm and humid.

Edited April 2 by Summer8906

[LetItSnow!]

 Summer8906 It would be the ultimate British irony if the Hadley Cell rose far enough to all but kill our winters but also grot up our summers as well. Instead of a future of 1995s, just a sea of warmer 1974s...

[Summer8906]

 LetItSnow! Indeed. Actually 1974 does closely resemble a cooler version of the typical weather conditions of recent years (not 2023 or 2024, though) with a mild wet winter, a dry sunny spring and an unsettled summer - so perhaps that "sea of warmer 1974s" has already happened. October 1974 is not typical of the modern October, though!

That said, I would accept a repeat of April and May 1974 this year. Probably a bit late now for the former in full, but say from mid-month onwards...

Edited April 2 by Summer8906

[Summer8906]

Back to the checking out of potential long wet runs, I've looked at 1965 and 1966.

1965 in particular looked like it was an exceedingly wet year - but no such long run. Both Feb and Oct were very dry; one or two other months were dry in the southeast. August, despite being cool and changeable, was slightly below average by EWP with the southeast exactly average. So just a 5 month run in 1965: March to July.

Then 1966 which I've heard associated with wet weather. It had less wet months than 1965; January, March, September and November were all dry making the longest run 5 months from April to August.

An interesting feature of 1966's wet period was how three consecutive months ended with a warm sunny spell which also saw in the following month: April, May and June. Strangely, 28 years later in 1994 with the exact same calendar (and 28 years is the calendar cycle), changeable months of April and May also ended with a warm sunny spell - the similarities between end April/start of May 1966 and 1994 are quite staggering.

That said summer 1966 was considerably worse than 1994, overall!

Jan 1967 was dry ending another possible run starting in Dec 1966 (and in another strange 28-year coincidence, the start of Jan 1967 sounds identical to the start of Jan 1995). Will come back with 1967/68 later.

Edited April 2 by Summer8906

[LetItSnow!]

 Summer8906 I'm also scrolling through the data, though just the EWP data for now. One thing I've realised from looking at the data is that, a lot of people have spoken about wet years in recent times having unusually dry months within them (see February 2023 for example) and how it's a sign of ever growing erratic rainfall, but historically it seems that a lot of these exceptionally wet years through times have been interspersed with very dry months here and there (further adding to the perhaps unprecedented run we're in now), so I don't think it's a new thing for us to see those rapid shifts within wet years.

Edited April 2 by LetItSnow!

[Summer8906]

 LetItSnow! Indeed. Let's hope it's not unprecedented for all time; I wouldn't like to exceed 1872's record and September to be the next dry month!

1998 was another more recent generally wet year but also featuring occasional dry months: strangely every 3 months (Feb, May, Aug and Nov) though July was dryish in the south.

I have a strong feeling that it might be unprecedented since the war though, as many of the years I thought of as wet are failing to reach even 7 consecutive wet months, never mind the 10 which now seems a certainty even if it's bone dry in the second half of this month.

For the 10 months to be reached or exceeded in 1965, Feb would need to have been wet (difficult) as well as August (easier; one extra active frontal system could have done it, perhaps). Dec 1964 was also wet so that would have given us a 10-month run, Dec 1964 to Sep 1965.

Interestingly the 1965 wet months were often cold cyclonic. Snow was quite a feature at times that year, with Jan, March and Nov all possibly producing significant lowland southern England snow - so it could safely be said that 1965 was a lot more interesting than 2023/24.

Edited April 2 by Summer8906

[LetItSnow!]

 Summer8906 I do think I'll live to see the first 1300mm EWP year on record. I'll probably live to see the first 12, maybe even 13C year in the C.E.T.

Also speaking of those extremes, 1852 was quite like 2020 because the spring was very dry; March and April only averaged 17mm and 20mm! May was near normal though. Yet the year averaged 1,213mm and had a 202mm November! Imagine if 2024 pulled a 200mm month out the hat. We haven't had one in 121 years. If any year was gonna do it...

I went through the entire data set and I cannot find anything longer than the 13 month period from January 1872 through to January 1873. The time length I could find closest to where we're at right now was 8 months, the exceptionally wet period from July 1960 to February 1961 as well as the infamous September 2000-April 2001 period. We've surpassed those though as we're onto month number 9. To break the (I'm assuming) record, we'd need to keep above normal precipitation until August 2024 and make it 14 months.

The all time averages for April through July are: 

April: 58mm

May: 64mm

June: 67mm

July: 79mm

August: 83mm

We wouldn't need a washout neccesarily to make it. With that the case, it would be fascinating to see if we break it, though knowing the chances we'd probably get a dry May scupper the chances. Not sure many would be sad about a dry month though! I kinda would like to see it be broken at this point as, as stated, we wouldn't need an absolute washout to do it.

Edited April 2 by LetItSnow!
Added incorrect and missing info.

[Summer8906]

 LetItSnow! Interesting, so 1872/73 was literally the only one to exceed the 8 months? We've already had 9 and it seems more likely than not we'll get a tenth, perhaps just from this week's rainfall alone!

(Was 2000/01 not also an 8-month wet spell, starting September?)

Edited April 2 by Summer8906

[LetItSnow!]

 Summer8906 Yes, you can add September 2000-April 2001 to that. I mistakenly miscalculated the January average (The all time average is only 82mm and January 2001 was 84.4mm so it technically counts). We've beat 1960-1961 and 2000-2001, pretty exceptional!

Unless I missed some, I couldn't see any that lasted more than 6-8 months. 

[A Face like Thunder]

 Summer8906 not in London, see my post of 23rd February

 

Edited April 2 by A Face like Thunder

[WYorksWeather]

 Summer8906 To be fair though, such summers have always been exceptional - 2018 and 2022 are amongst the hottest ever recorded, along with 2003 and 2006 at times. To have four such summers this century probably already indicates an increasing frequency.

I think there's a difference between what models predict for the distant future and the present. We don't see much of a trend for decreasing summer rainfall at the moment, but it comes up more as we head into the 2040s, 2050s and beyond as a possibility. Another 10-15 years of data before then might shed some light.

The cloudiness aspect I think probably comes as others have said from more Tm and rPm airmasses and fewer clear Pm and true northerly airflows due to the increasing Hadley Cell influence.

[LetItSnow!]

 WYorksWeather It's whether we end up shifting the HC far north enough to have a persistent influence. Indeed I can imagine summer rainfall overall not changing much due to those hot, dry summers being alongside very wet, humid and poor summers.

[WYorksWeather]

 LetItSnow! Yep, it's definitely possible. Of course, we won't know until 2050 whether the predictions verify or not 

[*Stormforce~beka*]

What's a Hadley cell.a battery?

[Summer8906]

 WYorksWeather Pure Pm definitely seems something of a novelty these days, whereas back in the 80s it was bog-standard, almost the default airmass.

A recent example being the weekend of March 23/24, which produced a bright and cool true Pm for a couple of days along with the classic spring hail showers on the Saturday. As I said, once as common as muck but now almost on a par with tropical continental for relative rarity.

A shame, as when true Pm gets in, the aesthetics are much better and you might achieve more than 2 hrs sun/day.

Edited April 3 by Summer8906

[Summer8906]

 LetItSnow! Perhaps, yes. To be fair I don't think the recent summers have been especially wet (in terms of volume of rainfall) compared to previous eras, just very dull and damp and lacking much in the way of northerly types of any description. 2021 and 2023 were the only two since 2012 which were really seriously wet.

So summers aren't getting wetter, just perhaps cloudier and damper (higher DP and RH) as already discussed. London and the far east of the country perhaps doing relatively well for sunshine though due to shelter from the interminable SW-lies, while in this area, and western/southwestern parts in general, the summers are disproportionately dull, damp and cool by day. August 2019 and August 2023 being two good recent examples of summer months where it's been cooler and cloudier here compared to other more eastern areas.

Edited April 3 by Summer8906

[damianslaw]

 Summer8906 Haven't the stats but we've had a number of thoroughly wet summers here since 2015, only 2018 and 2022 can be classed as very dry, 2021 quite dry. 

[Summer8906]

 damianslaw That would probably figure with the anomalous SW-ly type: hilly areas in the west would be especially wet.

Edited April 4 by Summer8906

[LetItSnow!]

 Summer8906  Summer8906 I averaged out the last ten summers (2014-2023) for the EWP and it basically came out average to the long term mean. Summers are definitely wetter compared to the 1990s, but 1990s summers were exceptionally dry (as a whole compared to average). In fact, the 1990s climate fit the idea of wetter winters and drier summers very well.

Out of interest I looked at the summer rainfall anomalies of the 1980s, 1990s, 2000s, 2010s and 2014-2023. Here are the results:

1980s - 210.5mm (92.1%) | Surprisingly, the infamous decade of summers ran pretty dry. None of the poor summers were extremely wet and some were drier than you may think, for example; 1981 had 141.4mm which is just 62% of normal and drier than all but four summers from the 1985 to 2023 (drier than 1989 too). 1986 was also slightly drier than normal despite that poor August.

1990s - 195.3mm (85.4%) | An exceptionally dry decade for summers with only three years wetter than average (The summers of 1992, 1997 and 1999). The infamous poor summers of 1993 and 1998 were both dry and the decade included the driest summer on record to date, 1995 with 66.9mm.

2000s - 228.8mm (100.1%) | This decade was running on a par with the 1990s for summer dryness up until 2006 with 2004 being the only wetter than average summer (yes, even 2002 was marginally dryer than average) but then the trio of very wet summers from 2007 to 2009 brought the count to very slightly over 100%.

2010s - 236.9mm (103.6%) | Whether a natural cycle back to wet, climate change induced or a mixture of both, the 2010s brought the return of regular unsettled summers, including 2012 which is the 4th wettest on records. The summers that weren't exceptionally wet tended to range from near normal to pretty wet and there were only two dry summers the whole decade, 2013 and 2018.

2014-2023 - 225.3mm (98.6%) | The loss of 2012 brought the total down and the very dry summer of 2022 alongside 2018 also added in reducing the averag, but that may be due to the wet summers of 2019 and 2020 not being into the exceptional category to balance it quite back to 100%. Still the signal remains changeable as 2023 proved to be a wet summer. 

Now we wait to see what the summer of 2024 will add to the table.

 

Edited April 4 by LetItSnow!

[Squally77]

While it's clear there's no particular trend in Summer rainfall, to get another summer month as cold as say, June 1991 or August 1986 for example, would only be possible as a result of a Volcanic winter. 

[Pulpstar]

Hi All,

 

I've had a look at this and played around with a  Google sheet from the England, Wales rainfall data.

 

It's been very wet over the start of the year (3rd wettest since records started in 1766 (2014 was the wettest start to the year) and after March we're currently ranking 5th of 1108 consecutive 12 month periods since daily records in 1931). 

Here's my work:

Weather - Google Sheets

DOCS.GOOGLE.COM

---

Daily rain record <a href="https://www.metoffice.gov.uk/hadobs/hadukp/data/daily/HadEWP_daily_totals.txt">metoffice.gov.uk/hadobs/hadukp/data/daily/HadEWP_daily_totals.txt</a> Daily England...

25 year moving average might move above a metre soon !

Edited April 5 by Pulpstar

[Summer8906]

 LetItSnow! I know what you mean about the 80s summers as it happens. They didn't seem that wet, with the exception of a few "bogeyman" months (June 1980, June and August 1985, August 1986, June 1987 and July 1988). I don't remember that many severely disrupted school holidays when I was stuck at home all the time, except 10 days of August 1986 culminating in "Charley". And the following year, August 1987, I actually remember as being mostly fine which - in contrast to contemporary summers - it was in the southwestern quarter of the country.

The main theme of many 80s summers was coolness rather than wetness.

Regarding summer 1981 I can well believe it was dry. I don't remember much rain (just a lot of cool and cloudy weather in June and July) and in fact the school holiday period was very dry and sunny, August 1981 being, IMO, better than any August in the past 20 years aside from 2022.

Same with summer 1993, it was only the final three weeks of July, the rest was generally dry though sometimes cool and cloudy.

I wonder how the 60s and 70s compare; the 70s obviously had 1975 and 1976 but also some more dodgy summers like 1974 and 1978. I can see how those of us whose first full decades of summer memories were the 80s and 90s might have the opinion that they have gone downhill recently!

Edited April 5 by Summer8906

[damianslaw]

 Summer8906 Though memories are quite hazy, I've commented before on how I don't recall much in the way of lengthy warm weather in the summers of 85-88 when I was 7-10 yrs old. Warm isn't the same as dry though, and we were often outside whatever the weather. Summer 89 though, what a treat!

Edited April 5 by damianslaw

[LetItSnow!]

 Summer8906

The 1960s - 227.3mm (99.4%) | The 1960s looks to have seen healthy variation between some fairly wet summers and some dry ones. 1960, 1966 and 1968 were very wet but none of the summers in either direction were record breakers.

The 1970s - 188.2mm (82.3%) | A very dry decade for summers, dryer than the 1990s! 1971 and 1974 were the only wet summers, the rest ranging from dry to exceptionally dry. Of course, 1976 was the driest summer on record at the time but now sits and 2nd place behind the aforementioned summer of 1995.

 

Perhaps comments of summers getting wetter is actually a reaction from a generation accustomed to dry summers? But that leads to an interesting question about longer term cycles, so here's the average summer rainfall for each decade for the 1900s up to the 1950s and see if we see any trend.

1900s - 226.3mm (99%) | Generally varied with few extremes except 1903 which was very wet.

1910s - 228.4mm (99.9%) | Once again varied, but with more extremes. Includes the wettest summer on record which is 1912 with 409.7mm. Also of note is how extremely dry the summer of 1913 was with just 114.4mm, only 50% of the normal. Only 1976, 1983, 1995 and 2022 have been dryer since. Also drier than 1911.

1920s - 230.0mm (100.6%) | Another varied decade, but 1921 was the only notably dry summer. 1927 was extremely wet with 336.8mm (147%), perhaps a bit of a forgotten dud summer. Might do a historic thread on that one.

1930s - 216.4mm (94.6%) | Perhaps not as dry as you'd think but there were a couple of really wet ones including 1930, 1931, 1936 and 1939 which somewhat offset the dry ones.

1940s - 204.1mm (89.3%) | Getting dryer... 1946 was the only notably wet one and 1949 was exceptionally dry.

1950s - 244.2mm (106.8%) | An unusual frequency of very wet summers despite a couple dry ones. 1950, 1953 and 1957 were wet while 1954, 1956 and 1958 were exceptionally wet.

So the trends show that the first 30 to 40 years showed little trend either way in summer rainfall, but a sharp decline occured from the 1970s until the mid-2000s, so it echoes my comment of: "Perhaps comments of summers getting wetter is actually a reaction from a generation accustomed to dry summers?".

I suppose it also adds more questions too. Was the period from the 1970s to the mid-2000s part of the warming trend where we expected to see a drying trend for our summers or was it a part of natural variability? Are the wetter summers of the past 17 years reverting to a wetter phase that'll last 30-50 years or is that climate change interfering with a natural dry cycle? So many questions and variables and not to be answered on this thread so please direct them there instead, but very interesting nonetheless.