B87

richie3846 We also shouldn't be set up for constantly below average sunshine and above average rainfall either, yet here we are. 2019 was the last year that had a fairly even mix of sunshine. Since 2020 it seems like we are usually below average, with 1 or 2 sunny months. 2022 was the only year since then where that sunny spell coincided with the summer.

richie3846 Temperature still needs to average above 20c though, and almost every year we get the 4 months of 20c. You'd expect to see some Septembers and Junes averaging below 20c, yet they are nowhere near as common as a sub 200 hour May-Aug.

We average 4 months with highs above 20c, and usually never have any trouble getting those 4 months most years. When it comes to the 4 months above 200 sun hours... nowhere to be seen.

Azazel And it looks like we will be very lucky to get 30 hours of sun from the first week of May. I mentioned yesterday that if we have a 200 hour sun deficit by the start of June, then we will need a repeat of summer 2022, plus a 230 hour September (which would be the sunniest on record), just to get back to the running average. Hopefully we get a dry, sunny October with an average high of 20c to make up for the lack of spring-like weather in the actual spring.

I don't want to see anyone cheering for a SSW to ruin spring ever again. 2 in a row now. Hopefully 2025 will be more seasonal regarding rainfall and sunshine.

SunnyG Then June manages to combine 1990, 1991, 1998, 2012, 2016 all into one.

TonyH That would also include recording sunshine the second the sun is above the horizon, which is not possible using the WMO threshold. You usually lose about 2 hours where the recorder will not detect anything.

So probably well into June before we see anything warm then. Last year the warmest day of the spring was only 22.7c. This year could be even worse?

Stabilo19 Because the new sunshine sensor under reports, so cant be compared to old data, or other locations in the UK or Europe.

raz.org.rain Not in summer though. Most deserts will still be 25-30c overnight. They can often get frost in winter. Las Vegas has a record low of -13c, which is the same as Heathrow. Albuquerque has colder average minimums that London from October until early April, (including an average January low of -3.1c which is colder than any part of the UK) and a record low of -27c. On the other hand, some desert climates are always warm, eg Djibouti has an average low of 21c in January and 31c in July.

Mapantz As of today, we have just equalled our March total after 24 days of April, which takes our annual total to 334 hours. May 2020 alone saw 330. danm They do, but only on the maps. They should have the actual values available without having to FoI request them.

CryoraptorA303 The absolute maximum recordable sunshine in London in July with no horizon obstruction is about 445 hours. Any obstruction at all and that number will be lowered.

Heathrow sun 1959 vs 2024 Jan: 76 vs 77 Feb: 55 vs 53 Mar: 104 vs 103 Apr: 139 vs 115-125? May: 221 vs ? Jun: 232 vs ? Jul: 277 vs ? Aug: 240 vs ? Sep: 209 vs ? Oct: 150 vs ? Nov: 53 vs ? Dec: 30 vs ? It is theoretically possible, just very very very unlikely.

CryoraptorA303 Assuming we start the summer with a 200 hour deficit, even a repeat of summer 2022 (June 242 hrs, July 250 hrs, August 263 hrs), would need us to see a 230 hour September (which would be the sunniest on record - 2018 saw 210 hours).

TwisterGirl81 350 hours in definitely possible on the south coast, and has happened before in hot/sunny summers. Heathrow has seen 3 months with more than 300 hours of sun. May 2020 (330 hours), May 1989 (310 hours), and July 2006 (302 hours). We are due a 300 hour June or August. The sunniest June was 294 hours in 1975, while the sunniest August was 295 hours in 1995.

Addicks Fan 1981 Between 1991-2023, 2007 was actually the 11th sunniest year with 1703.5 hours. Helped by a very sunny March/April, a slightly sunnier than average August, November and December. At Heathrow, April 2007 absolutely demolished April 2021 in sunshine totals.

TwisterGirl81 The values on the Met Office historic data page, and Meteociel, are the raw values (at Heathrow at least, probably the same for most locations). The true values are the ones used to create the monthly anomaly and totals maps.

CryoraptorA303 December was notable as it was the 3rd dullest on record at Heathrow, after 1969 and 2010. May wasn't that notably sunny, it saw 221 hours vs the average of 208 hours. A full day of sunshine would account for that. If June hadn't been very sunny, the year would have seen around 1590 hours of sun, which would have made it one of the duller years since 1990. It looks highly unlikely that we will claw back the 140ish hour deficit that we will be on by the end of April, by the end of the year, with the first half of May looking unsettled as well, we could have a 200 hour deficit by the time summer starts. danm I only got those 2006-2020 true values as I put in a FoI request to get them.

danm I got the 2006-2020 corrected values from the Met Office, then looked at the average correction for each month in that time period. The method I use now probably isn't 100% accurate, but it always matches up with the monthly sunshine maps that use the true values. To get a good idea of the true value, multiply the raw values by the following numbers (other stations might have different conversion factors): Jan: 1.076 Feb: 1.080 Mar: 1.080 Apr: 1.090 May: 1.124 Jun: 1.141 Jul: 1.129 Aug: 1.122 Sep: 1.099 Oct: 1.091 Nov: 1.077 Dec: 1.068 CS0044355 Heathrow Monthly Sun Hours 2006-2020 (002) (1)-1.xlsx

danm The Met Office historic data page and Meteociel for daily values. The sunshine needs to be corrected by about 6% in December, up to 14% in June. In April the true value is 1.1x the raw value.

richie3846 It was a few hours below the average. It's only really because of June that it got anywhere near the average.

danm Yet we still ended up below average for the year. A single extra sunny day between Nov-Feb can result in a month with 120% of the average. Addicks Fan 1981 Both cool by day and chilly by night, not ideal for being outside if there is any breeze or cloud at all. I recall August 2007 feeling more like September than August.

baddie What you hope will happen or what you think will happen? That May to October period sounds like 1959 or 2003, and would be extremely unlikely I feel. I think May 2024 will be like a wetter and duller version of last May. Wouldn't be surprised if June to September was like 2016, but worse. An atrocious June, a so/so July, August to be the best month but not great, then a warm but very dull September. October will probably be like most Octobers these days. Mild, extremely wet and with less than 100 hours of sun. By the end of the year, we will have seen less sun than 2021 (currently the dullest year on record).

baddie As long as it also gets typical spring rainfall amounts. While autumn 2023 was slightly sunnier than average, it was also extremely wet. Ideally a 200 hour September with very little rain, a 170 hour October with less than 30mm and a 100+ hour November with less than 40mm would help. We are overdue a long long run of dry months.

TwisterGirl81 It was only really June that was meaningfully sunny last year. You can get a 120% sunny January or February just from 1 or 2 extra sunny days compared to normal. Overall, 2023 had slightly below average sunshine and well above average rainfall. It was the wettest year since 2014 and the 3rd wettest on record. If we actually saw the conditions we normally get over the last 2 years, there wouldn't be any pessimism around like there currently is.