Worryingly Wet & Worryingly Sunless

[CryoraptorA303]

 danm It wasn't that. Those August thunderstorms more or less missed the deep SE. I think November in particular was extremely wet in the SE, so that's probably what took it above.

Out of interest, here are all the months:

As I suspected, November and to a lesser extent December were especially wet in Kent and Sussex, and the east coast of Hampshire, so the anomaly is probably coming from that.

Aside from that, February is really the only month until September that saw significant rainfall in the deep SE all year. Keep in mind that average rainfall in spring is already quite low in the SE quadrant, so a single major storm passing through could bring rainfall totals to near average, even if no rain falls on any other day at all. May was overall quite a humid month, perhaps what you could expect February 2024 to look like in May, just without so much rainfall.

One thing I will mention though is I have no idea where that still-dry-but-less-dry-than-the-surroundings in Kent anomaly comes from in July. I don't remember any significant rainfall all month and I'm only down the road from East Malling where the rainfall would've been picked up. I remember a single rainfall from the entire period July-early September that was either in late July or earlier August and it was a light shower that would've deposited perhaps a few mm. The first major rain I remember was in early September when big scary sounding thunderstorms started moving over and dropping bombs for about 10 minutes at a time. Perhaps overnight there were a few light to moderate showers over the month that brought rainfall totals up slightly. May I don't remember any rain at all but the anomaly mostly looks like a single big thunderstorm moving through which could have happened overnight. All the other months check out with what I remember.

[danm]

 CryoraptorA303 yep that explains it. November and September too. 

[kold weather]

 danm that would personally be my reading of things.

the only real way to know 100% would be to look at rain days and what the numbers look like. You could convicably have less rain days but higher average. Of course in recent years with sluggish broad patterns such setups are producing exceptional spells on a fairly regular basis

[danm]

 kold weather The Met Office anomaly maps do show rain days above 0.2mm, above 1mm and above 10mm and how that compares to the long term average, but only month by month rather than on an annual basis. 

 

[CryoraptorA303]

Someone call NASA, there's a strange object in the sky!

[CryoraptorA303]

So I've fairly quickly drafted up what I would like to see as my ideal April this year. Normally I wouldn't want to see the temperatures I'm going to put here, but 1. it's good to get the extremes out of the weather's system before it's summer proper, and 2. we need a warm, very dry month to start seeing all the nasty groundwater on its way.

"April 2024":
1st: 13.7°C Hereford
2nd: 12.5°C St James's Park
3rd: 13.1°C Exeter
4th: 12.9°C Pershore
5th: 18.6°C St James's Park
6th: 23.8°C Pershore
7th: 26.6°C Frittenden
8th: 21.7°C Santon Downham
9th: 18.4°C St James's Park
10th: 15.3°C Exeter
11th: 19.6°C Heathrow
12th: 19.3°C Benson
13th: 25.4°C Frittenden
14th: 23.1°C Herstmonceux
15th: 17.6°C St James's Park
16th: 18.1°C Santon Downham
19th: 23.2°C Coningsby
20th: 27.3°C Wisley
21st: 25.9°C Heathrow
22nd: 24.4°C Otterbourne Waterworks
23rd: 25.2°C Herstmonceux
24th: 22.8°C Wellesbourne
25th: 23.6°C Heathrow
26th: 25.4°C Wisley
27th: 28.5°C East Malling
28th: 24.2°C Weybourne
29th: 17.2°C Chivenor
30th: 16.5°C St James's Park

Bold would be daily records.

The month would start with average to below average temps for many, and perhaps some very light showers in some areas. Things quickly become settled as much warmer conditions move through over the 7th. Some very light showers on the 10th but nothing to worry about that. The country then sees its longest dry spell since last year with virtually zero rainfall for anyone over the period. Some showery breakdowns over the 28th and 29th, but again fairly light considering everything.

Ideally hot southerlies will only be drawn on the very hottest days and humidity will remain low, allowing for nights to not be overly warm in the period and preventing any massive thundery breakdowns and also making sure I don't end up being too uncomfortable in this spell of heat I have ordered out of character. In theory this should also stop the Atlantic from being microwaved if air temperatures significantly decline at night and prevent the signal strenghening again over May and June. April 2011 tried this at first but in the second half got impatient and went for the persistent blocking route instead, and May really messed it up by having the northerly jet so the cyclones could continue to build and finally hit us over summer. In an ideal world May would've been significantly less dry for the south as well as Scotland so the April buildup was out of the Atlantic's system and then summer could've continued on April's note. Most very hot summers in our history did this, sacrificing May for the summer, including 2003 and 2022, and 2019 attempted it but got the timing a bit wrong so we were still hit by a lot of cyclonic activity, despite the high temperatures over late June, July and parts of August.

Overall this April will be the 10th driest since 1884, being slightly drier than 2020, and no more than the 5th warmest on record owing to nights not being out of control.

Hopefully this will be enough to get rid of the excessive moisture, but May and June will have to keep it up with the dryness before July or August could be allowed to be average or slightly wetter again. Ideally the whole summer is modestly dry (as high temperatures will of course act as a counter to water settling so intense aridity is not as pertinent) but average can also work if AMJ was very dry overall. As for autumn, this would be a good time to have that overdue notably dry autumn with a late summer extending into September and seeing it as one of the 10 driest, and then October and November are average to dry as well, but as long as averages are roughly kept to, we should not be facing the same level of problems we are right now come next year.

You'll also notice that the warm spells are very SE quadrant-centric. Normally I'd like to give more daily maxima to the other hotspots like Pershore, Benson etc., but this time the SE really does need the highest temps of the warm spell. I'm sure overall it's still very warm for other regions.

Edited March 18 by CryoraptorA303

[Summer8906]

 CryoraptorA303 I hope you're right for dryness!

Struggling to see synoptics in early spring that would lift the absolute max from 13 to 27 in three days though, and following a relatively sustained cooler spell (assuming it starts this Friday and continues into April as shown above).  Normally in April, high temps come after a long period of dry sunny weather so the air has a chance to gradually warm and the ground becomes very dry. The 2007 and 2011 hot spells for instance came after weeks of fine, dry weather. Also the saturated ground would presumably knock temps on the head, difficult to see how we could get almost 27 in early April with ground as saturated as now.

Edited March 18 by Summer8906

[Freeze]

6 hours ago, danm said:

A couple of localised patches very slightly above. It may be as simple as a couple of summer thunderstorms in those areas upping the totals.

My area is under the slightly wetter than average anomaly on that map of 2022, we had loads of thunderstorms during that summer/ autumn.

[CryoraptorA303]

 Summer8906 I would've also said the same about reaching 19.9°C in NW Scotland in January after late October-early January had been a total jaffa cakes-up, or Pershore and Teddington reaching 18.1°C in February after late January onwards had yet another massive jaffa cakes-up, but here we are.

Ground conditions definitely have an impact on temperatures, but it's not as much as people think and I'd argue a lot of the impact is in how long-lived a spell is over the actual maximum temperatures reached. In July 2019 groundwater was above average but we still reached 38.7°C for a day with ~20°C uppers. The difference between that and say August 2003 is the July 2019 spell died much faster while August 2003 kept its potential for nearly two weeks. And wind direction wasn't a factor here in the temperatures reached, if anything it was more ideal in August 2003. Here in this hypothetical spell you can see we get a hot southerly and temps are whacked up for a day or two before the potential is completely killed off as all the heat is transferred to evaporation. By later April it's been dry and warm enough that the next big southerly has more staying power and once the high establishes we can stay above 20°C.

Another thing here is a big warm spike would encourage flora to aggressively bloom and they'd also be helping in drinking some of the water on the ground.

Also important to keep in mind southern Europe is in the opposite situation to us, so hot air from the south will be getting no challenge there before it's shunted into us, if that's the course it takes.

[LetItSnow!]

Long post coming up but I thought it's interesting. Mods can move this if they think it's better somewhere else.

The "is it getting wetter?" question is interesting, so I thought I'd put the anomalies of each decade of the past 100 years, though since we're only in 2023 I'm doing it like 1914-1923, 1924-1933 etc. The anomaly I'm using is the all time UKP average from 1766 to present day so it takes into account all wetter and drier phases. Also, since these are just slices of ten years in time you could say it's rather arbitrary, but it's a crude way to see if the percentages are going up or whether they fall in line with natural variability.

The all time annual rainfall average is 922mm.

1914-1923: 926.4mm (101%)

1924-1933: 962.7mm (104%)

1934-1943: 912.8mm (99%)

1944-1953: 914.6mm (99%)

1954-1963: 931.6mm (101%)

1964-1973: 910.1mm (99%)

1974-1983: 929.2mm (101%)

1984-1993: 925.6mm (100%)

1994-2003: 969.2mm (105%)

2004-2013: 956.3mm (104%)

2014-2023: 1012.1mm (110%)

Interesting things to point out: 

The UK has always had a cyclical pattern between dry spells and wet spells, often alternating between them every 3 to 10 years. In the earlier part of the record when temperatures were a lot colder, this pattern still occured but often with the die loaded towards dryer than average conditions. In the 20th century both ends became more extreme with stark contrasts in rainfall between decades; for example, the 1910s-1920s was generally wet, but the 1930s-1940s generally dry, the 1950s and 1960s saw the polarisation increase even more, particularly the 1960s when the first half of the decade was very dry, but the second half exceptionally wet. These polarising extremes reduced into the 1970s, 1980s and into the first half of the 1990s as the wet spells and dry spells became shorter, leading to more of an "average" results. From the late 1990s onwards as temperatures have increased the results are showing the same as the earlier half of the record, but instead of the die loaded towards dry it's now loaded towards wet, which makes sense as warmer air holds more moisture and our climate is dominated by the Atlantic. However, despite the past ten years being anomalously wet, it isn't unprecedented; 1874-1883 had an average of 1017.2mm despite occuring in generally dryer times, which means despite the die being loaded in favour of one outcome, natural variability will still be at play.

The moral of the story; we're getting wetter, but don't rule out an anomalously dry period that lasts 5 to 10 years, but err on the side of wet being perhaps the "norm", at least for the forseeable future (next couple of decades; the effects of a moving Hadley Cell and other unknown variables may change this outlook into the latter half of the 20th century, but if our Atlantic remains dominant then expect those storms to be juicer than ever!).

[CryoraptorA303]

As a supplement to my previous post, allow me to demonstrate a proof of concept:

This is April 2018. After a very wet March and a wet start to April (and I'm pretty sure it'd been wet all-around since July 2017), in the space of a week, temps jumped all the way from ~12°C to 29.1°C, the highest ever reliably recorded in April.

After another short spell, the weather became astoundingly anticyclonic and summer 2018 was one of the hottest and driest on record.

It really can turn around this quickly, and as far as I know there wasn't a drought in southern Europe allowing hot air free access north that time. Global temps are much higher than 2018 at the moment.

The bigger issue at the moment will be getting the Atlantic signal down and keeping a high above us.

Edited March 18 by CryoraptorA303

[B87]

 Summer8906 29c in April 2018 came after weeks of absolute cold, wet and dull rubbish!

[kold weather]

You only have to look at how rapidly things shift in a continental airflow to know of course things can shift pretty drastically. It's just far more rare here as we are surrounded by water which will always nerf extremes.

 

[CryoraptorA303]

 kold weather Unless that name's extreme is "Coningsby"

[SunSean]

Just got back from holiday & the weather in England is exactly the same as when I left including the week ahead forecast lol. 

Going to miss those glorious blue skies from Tenerife!

Looks much more vibrant, happy & beautiful than a constant blanket of grey don't you think?

[danm]

 CryoraptorA303 yes it switched very quickly in 2018. BFTE, mini BFTE, a very wet and cool end to March and start to April and then a sudden switch to warm/hot and sunny. We didn’t look back after that, and the Summer was a classic. 

[richie3846]

 LetItSnow! It surprised me how little variance there is between the 10 year periods you selected. Taking into account the 7% more rain per celcius formula, that is often cited these days, the rainfall patterns appear to be virtually static, even over the last 3 decades you provided. 

I noticed the same pattern on the rainfall chart someone kindly posted a few days ago in this thread. While there is a slight upward trend overall, the cyclic pattern is very clear. Our rainfall patterns are pretty well defined over a period of time.

[LetItSnow!]

 richie3846 The little variance in the percentages hides large differences as stated. If I had selected years from before then it would be relatively dryer. Variability as part of the cyclical pattern has always existed but seemed to be rather more polarised in the mid-20th century.

[kold weather]

Interestingly on the rainfall front looking a the UK as a whole, since 1931 7 out of the wettest 10 years across the UK as a whole average have been since 2000. Considering thats over 90 years of records, to have 70% of them be in a 23 year period is pretty telling in itself...and I think a little high to be just coincidence.

 

 

Edited March 18 by kold weather

[Daniel*]

6 minutes ago, kold weather said:

and I think a little high to be just coincidence.

It’s not coincidence 

[raz.org.rain]

 B87 when I was a kid I always had this impression that a heatwave in spring would result in a poor summer, but perhaps my perception was shaped by that run of poor summers we had in the late 2000s. Come to think of it, we've had numerous years where we've had a good spring and a good summer combination. 

[CryoraptorA303]

 raz.org.rain I think the key is moderation, with something like 2003 or 2022 instead of absolutely unhinged spells like 2007 and 2011. Sacrificing May seems to be quite important as well - Can anyone here find a significant May spell that then led to a sunny and/or dry summer? I highly doubt it. 2010 is the closest we've ever been IIRC.

Edited March 18 by CryoraptorA303

[raz.org.rain]

 CryoraptorA303 by the sounds of things, we stand a good chance of seeing a good May and good summer combination this year. I seem to remember May 2022 was decent for warmth too.

[MP-R]

 CryoraptorA303 Depending on what you mean by significant, 2018, 1995 and 1990 come to mind. The nineties examples were week long spells though.

[CryoraptorA303]

 raz.org.rain Funnily enough, May 2018 is the third hottest and we know how that summer turned out, so it's not completely absolutely impossible to have a hot May follow into a hot summer. I'd rather the big heat spikes come in April though before they have the potential to start getting stupid hot, and then May and June can just be pleasantly warm but not extreme. July-September though I have a feeling will be extreme no matter what, it's either 2023 again or they're going to be (imo) way too hot. A third of me is still betting on that consecutive September annual max.

If I had to choose which hot summer to repeat though, it would definitely be 2018. That one seems to have been the least bad for me out of the ones in my lifetime, and in the grand scheme of things it didn't see any absolutely psychotic temperatures like the others in this century have. I wonder how having April significantly drying up instead of waiting until May to go from jaffa cakesfest to bonkers would affect it though, if that happens we could start seeing the 36°C demon turning up later in July or early August.

I imagine if we had for example May 2018, summer 2010 but with August replaced with 2022 instead, and then some sort of frankenstein of Septembers 2014, 2016 and 2020, people would be quite happy with that. We probably would end up with September reaching >35°C in that scenario and getting us the consecutive September annual max. Adding one of the psychotic Aprils into that would probably seal the deal for most, but that's likely not a plausible coalition. My proposed April is the best you're going to do if you want the rest, otherwise the Atlantic is getting microwaved and will make July onwards impossible.

Edited March 18 by CryoraptorA303