- 2 days ago
This is an in-depth Met Office UK Weather forecast for the next week and beyond. Temperatures are rising across the UK as high pressure builds from the south. Many places will be dry with sunny spells this Bank Holiday Weekend but how hot it actually gets will depend on where and when thundery downpours take place, especially during Saturday. Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:00Air, similar location, mid-Atlantic, but it's not at four kilometres height.
00:06So what's going on?
00:08Essentially, what's going on is that the air that ends up being hot over London at the surface on Friday
00:17descends much further down the atmosphere.
00:19It comes from higher above, and then it starts to sink because of the high pressure at the upper atmosphere
00:26and the high pressure at the surface.
00:28That high pressure takes the air from four kilometres and pushes it down to the surface.
00:35It compresses it.
00:36So all these layers of atmosphere, we'll go back to Friday, all these layers of atmosphere are being squeezed.
00:43You can see that squeeze four kilometres down to the surface, all being squeezed down to a much shorter
00:51or much lower thickness part of the atmosphere.
00:54And when you squeeze air, when you compress it, it's called, meteorologically, adiabatic compression or adiabatic subsidence.
01:04When you squeeze it, it warms up.
01:08Have you ever pumped up a bike and felt how hot the valve is?
01:12What you're doing there is you're squeezing the air.
01:14It heats up.
01:15And that's because if you take a parcel of air and compress it, there is less space for the molecules
01:21in that air parcel to move around.
01:23So they're bumping into each other more.
01:24The temperature rises.
01:26That's what's happening.
01:27So, no, we're not importing the air from the south.
01:30We're just seeing the air from the Atlantic become squeezed under high pressure.
01:35How common is this?
01:37Well, here's an interesting paper from 2019 from the Quarterly Journal of the Royal Meteorological Society.
01:45It was a study that looked at heat waves across many parts of Europe from 2079 to 2016.
01:53And what caused them?
01:55Was it air that was moving from somewhere else, known as advection?
02:00Was it adiabatic heating, where the air is sinking under high pressure?
02:05Or was it diabatic processes would be where the sun is shining and drying out the soils and the air
02:18is rising as a result?
02:19Now, just to explain, adiabatic means that the atmosphere isn't gaining or losing heat from elsewhere.
02:26It's simply warming up as a result of being squeezed or compressed.
02:30Or when you get rising air currents, it's cooling down because the air is rising through the atmosphere and cooling
02:37as a result.
02:37So that's what we call adiabatic heating or cooling.
02:42It's where you don't take hotter air from elsewhere and that's why it warms up.
02:46It's just warming up in situ because it's sinking or rising.
02:50So, diabatic processes are where the air is getting some heat input, i.e. from the sun.
02:57And this paper was interesting because it looked at various regions across Europe and it found, I've highlighted it here,
03:04in all regions, horizontal temperature advection is almost negligible.
03:08In other words, high temperatures for European heat waves are almost always not caused by hot air being blown from
03:17somewhere else.
03:20But in the UK, it says, subsidence and adiabatic warming are of first order importance.
03:29In other words, most of the high temperatures we get in the UK are caused by that compression, high pressure
03:35sinking air rather than air being imported from elsewhere.
03:40An aside to this as well, they looked at Western Russia and they found that diabatic processes were more important.
03:47Solar heating and a very local transport and, you know, turbulence of the air and so on.
03:53So, really interesting study.
03:56I do recommend it if you're interested in what causes heat waves in the UK, what causes high temperatures.
04:01But that's something that I thought was worth pointing out for this.
04:05Now, how hot will it get in the UK as a result of that adiabatic compression?
04:13Here is a summary of the expected temperatures during the next few days.
04:19Let's take this off and let's go through them.
04:21So, Tuesday, it's already feeling a bit warmer out there compared with the northerlies that we had last week.
04:26But, of course, tempered by the fact that we've got a lot of showers across the UK.
04:30So, we're getting up to the 19, perhaps 20 Celsius mark Tuesday.
04:33By the time we get to Wednesday, 21, perhaps 22 Celsius.
04:37Mid to high teens widely.
04:39So, feeling warmer.
04:40Temperature's not far from average.
04:42A little bit warmer in the east.
04:43A little bit cooler further west.
04:45By the time we get to Thursday, and again, still a lot of cloud, especially for northern parts of the
04:51UK.
04:51And still some showers or even some longer spells of rain for the likes of Northern Ireland, Scotland, Northern England
04:57at times.
04:58So, yeah, Thursday's warmer again, but it's not entirely dry and sunny.
05:03The driest and brightest weather will be towards the south.
05:05But you can see how those temperatures are rising by Thursday, up to 24 Celsius in London and the southeast.
05:1122, 23 for eastern England, up to 20 Celsius or so, or a touch more, across eastern Scotland, as well
05:18as Wales and western England.
05:20But Friday, those temperatures jump significantly.
05:24By Friday, we're talking about mid to high 20s widely across England and Wales.
05:31The highest temperatures, once again, eastern and southeastern England.
05:37But temperatures creeping up to 20 to 24 Celsius across northeast England and eastern Scotland.
05:42Always, always going to be cooler towards the north and northwest of Scotland.
05:46Mid teens here, but widely across the UK.
05:49We're into the 20s at least, and the mid to high 20s in the south and southeast.
05:55Now, Friday is going to be widely sunny.
05:57We've got the surface area of high pressure over the UK.
06:00We've got that upper high pressure over the UK.
06:03So, it's a fairly straightforward one.
06:06By Saturday, the most likely temperature in the southeast is 28 Celsius.
06:13Mid to high 20s widely elsewhere.
06:16And similar values compared with Thursday for Scotland, northern England and northern Ireland.
06:22But there are increasingly, by Saturday, some complications.
06:27Now, both Friday and Saturday have the potential to be even hotter.
06:33I said the most likely temperature was 28 Celsius.
06:35There's a 20% chance on Friday and a 20% chance on Saturday of 30 Celsius, again, towards the
06:44southeast.
06:45But on Saturday, what we call the spread of temperatures in the computer models is even larger.
06:56So, this is the temperature trend for London.
06:58And I'm focusing on London because that's likely to be one of the hottest places in the country during the
07:02next few days.
07:03So, it's a good example of how temperatures are rising, the kinds of extremes we might see, and the uncertainties
07:10involved heading into the weekend.
07:11This is London, and this is from the European model, the temperature trend.
07:15This is taking into account 51 computer model runs, and it plots the results in terms of box and whiskers.
07:22Red for daytime maximum temperatures, blue for overnight minimum temperatures.
07:27And you can see the red line here in bold, that's the average, so it's 17, 18 Celsius.
07:34And we're bang on average pretty much Tuesday and Wednesday, and then it's rising.
07:39These boxes are rising.
07:40Friday, well above average, close to the more extreme values that we see in past years.
07:46And by Saturday and Sunday, those boxes are, again, significantly above average.
07:53But Friday's box is really small, so we can be reasonably confident about Friday's numbers.
08:0028 with a smaller chance of 29 or 30 Celsius.
08:03But by Saturday, most likely, it's going to be similar to Friday.
08:09But there's a chance that it'll be higher, also a chance that it'll be lower.
08:13And the reason for that is because there are some showers developing as we go into Friday night and Saturday.
08:21They will introduce more cloud, and obviously, where showers do fall, they're going to introduce cooler air as well.
08:29So, Saturday's temperature is highly dependent on where those showers will fall.
08:34But at the same time, the air is getting hotter, despite the increased chance of showers.
08:42Let's take a look at what's going on.
08:44Friday, if we turn off those layers and put on a closer look at the jet stream, it will make
08:52it a little bit clearer.
08:53Friday, we've got this upper ridge, this upper area of high pressure.
08:57You can see the jet stream, the winds at jet stream level going around the UK like so.
09:02So, upper high and surface high close to the UK, widely settled weather.
09:11But out here, you can see this upper trough, this dip in the jet stream, and that's approaching the UK.
09:17And as it approaches, it gets sharper.
09:19It pushes, digs south and gets narrower.
09:22And it's this upper trough that is the fly in the ointment by the time we get to Friday night
09:28and Saturday.
09:30Because as that approaches, then we've got a couple of things going on.
09:34We've got a hot plume of air ahead of it, high temperatures and high humidities.
09:41We've also got rising air as this upper trough approaches, especially on the forward side of it.
09:50Why do you get rising on the forward side of it?
09:52Well, as it's narrowing and dipping south, it squeezes the winds together.
09:56And we get this strengthening of the winds in the upper atmosphere around here.
09:59That removes air from the top of the troposphere.
10:04And you get this vacuum effect.
10:06So you get this area just ahead of the upper trough where the air is forced to rise.
10:12And, of course, with the high heat and the high humidity at the surface, that adds energy.
10:18You've got this energetic rising air.
10:20So it's just ahead of this.
10:22Here we are, 5 a.m. Saturday, where we've got a front and the chance of some showery rain and
10:33some thunderstorms.
10:34Just to give you an idea of the chance of rain and thunderstorms, this shows, between Friday night and Saturday,
10:42those areas most at risk from some heavy downpours.
10:47It's very blocky because it's taking a number of computer models and working out some complicated calculations.
10:54But, essentially, it's showing that it's eastern parts of the UK that are more likely to see some heavy downpours
10:59on Friday night into Saturday.
11:01And then this graphic here, similar sort of thing, but it shows on Friday night into the early hours of
11:08Saturday, the likelihood of lightning.
11:10And this is actually quite a high probability across eastern parts of the UK for this lead time.
11:18So Friday night, and it's highlighting the Midlands, East Anglia, and the southeast as that narrowing upper trough moves in,
11:25increased chance of showers.
11:27And that remains with us on Saturday.
11:32If I move it forward a little bit, you can see 3 p.m., this dip in the upper troposphere
11:41wind arrows, indicating that we've got this instability higher up that's going to cause rising air.
11:48But, of course, showers and thunderstorms always hit and miss.
11:51At the same time as that dip coming along in those winds, we've got the plume of heat and humidity
11:59intensifying.
12:01So two things going on.
12:02The personality of the air, or the potential of the air, turning even hotter on Saturday.
12:07So if you didn't have any showers, if you didn't have any thunderstorms or cloud surrounding them, then there's the
12:15potential for temperatures to get to 30 Celsius in the southeast, a higher potential compared with Friday, because the inherent
12:22characteristic of the air is hotter.
12:24But you've also got that increased chance of showers and thunderstorms, and if they directly hit those areas that are
12:31more likely to be hot, then they'd end up being cooler.
12:34As a result, more cloud, more showers, cooling things off.
12:37That's why there's this spread in temperatures on Saturday that we don't see on Friday.
12:40Friday is much more straightforward with the high pressure in the upper atmosphere and the surface.
12:46Now, how common are temperatures like 28, 30, 32 Celsius?
12:54It's worth showing this to put it all into context, because the most likely temperature, as I say, Friday and
13:00Saturday, 28 Celsius.
13:01And this shows the occurrences of 28 Celsius since 1931.
13:07And essentially, there are too many occurrences to fit on the screen here.
13:12So, we've only got the most recent years, the most recent, 1st of May, last year, 2025.
13:19Let's go back to that, sorry.
13:23Most recent, 2025, 1st of May, and then 2020, there were three days, 2018, and so on, all the way
13:30back to 2003.
13:32But there were many more years before that, going back to 1931.
13:36So, yeah, every few years or so, we get 28 Celsius or more in May.
13:42But, looking at the threshold of 30 Celsius, and this shows the number of years, or the number of days
13:48in May, rather, since 1931, that 30 Celsius has been recorded.
13:53Over here, by the way, there are the number of weather stations that recorded that value.
13:58And there are only six years in total, with some years seeing a few days, like 1944, 1947, but six
14:08years since 1931, in which 30 Celsius or more has been recorded.
14:12So, that's relatively unusual.
14:14It's not unprecedented, but it's relatively unusual.
14:16Last time, 2012, I should say.
14:19Now, this is where you make the threshold 32 Celsius.
14:24It's only ever happened on one day in May, back to 1931, and that was the 29th of May, 1944.
14:31The record breaker, in other words, the highest temperature in May on record, 32.8 Celsius.
14:38That's very unlikely this weekend, but like I say, 20% chance Friday and Saturday of 30 Celsius, which would
14:45be fairly unusual, but not unprecedented.
14:49In terms of whether or not that would then classify as a heat wave, well, Friday, yeah, we're likely to
14:58breach thresholds for heat wave conditions.
15:02And that's where we get a temperature exceeding a certain value, depending on where you live.
15:09And that value is shown here, northern England, Scotland, Wales, southwest England, northern Ireland, it's 25, and then towards the
15:16southeast and around London, it's higher.
15:19So, 28 Celsius, for example, London up through Cambridgeshire and so on.
15:22So, Friday, we're likely to exceed those values, but for a technical heat wave, you need those values to be
15:27exceeded for three consecutive days.
15:30Saturday, a bit of a question mark in places, especially around the southeast, because of the increased chance of showers
15:37and cloud from those showers, but always the chance that will, again, exceed those thresholds.
15:41Then into Sunday, there's a small question mark over how much the hotter plume will get shunted away and how
15:51much temperatures will rebound to similar kinds of values compared with previously in the weekend.
15:59And then, of course, we've got bank holiday Monday.
16:01More on those two days in a sec.
16:02I just want to quickly go over nighttime temperatures as well, because they are another remarkable aspect of the forecast.
16:10And these are the minimum temperatures.
16:13We're already seeing milder nights next few nights, temperatures back in the double figures and the teens after remarkably low
16:19temperatures overnight last week.
16:21But if we skip ahead to the start of Friday, we're talking about mid-teens.
16:27Start of Saturday, look at 19 Celsius, it's showing.
16:32For London.
16:33Now, to put that into context, the record overnight minimum temperature in May in the UK is 18.9.
16:40That was Folkestone.
16:41So if 19 Celsius is the overnight minimum temperature, and it's most likely somewhere like London or somewhere just downwind
16:51of higher terrain like North Devon, North Wales and so on.
16:56And if that temperature overnight doesn't drop below 19 Celsius, then it would be the warmest May night on record.
17:0717 Celsius for the start of Sunday.
17:09But it's complicated by the fact that you need the right weather station in the right location to sample those
17:14areas that can be very localized, but very warm overnight.
17:18And also by the fact that you need a 24-hour period in which the temperature doesn't drop below those
17:25values.
17:25So you basically need two warm nights in a row in many instances.
17:30So something to keep an eye on.
17:31But there is that chance of some very warm, oppressive feeling nights coming up.
17:38On to Sunday and Monday, because the forecast actually becomes a little clearer later in the weekend.
17:46The one complication is the position and the effect of the showers on Saturday and any thunderstorms that come along.
17:54But by the time we get to Sunday, that, let's put that back on actually, it shows it quite nicely.
18:05There's the narrow trough moving across the UK through Saturday.
18:10It then pushes through.
18:12End of Saturday, it's out of the way.
18:14We've got a ridge of high pressure building in again.
18:18Oh, what happened there?
18:19I've never seen that before.
18:21Okay.
18:23And that ridge of high pressure will settle things down once again.
18:28And high pressure will build at the surface again.
18:31But the main uncertainty actually going through Sunday and into bank holiday Monday is not necessarily how much sunshine and
18:40how much dry weather will get.
18:41Yeah, there'll be some rain through Saturday and into the start of Sunday in the far northwest.
18:45But otherwise, high pressure will return and settle things down.
18:48The main uncertainty is whether that hot plume will return into the south early next week.
18:55And here's another thing to look at.
18:59This is Tuesday, midday, and this is from the European model.
19:04And it shows high pressure firmly across the UK.
19:08And in fact, I can click on any number of these.
19:10They mostly show the same thing, high pressure sitting close to the UK.
19:15So you can see a very settled start to the week.
19:17But one difference between all these different computer model runs is the position of that high.
19:23And that's going to be crucial.
19:24So Sunday, Monday, just want to emphasize a lot of fine weather out there.
19:28And you might not really care whether it's going to be 26, 27 degrees or whatever.
19:33It's going to be mostly fine for the bank holiday weekend, especially through Sunday and Monday as high pressure rebuilds.
19:39But this is just one aspect of the forecast that is quite interesting to look at.
19:44Because I mentioned the heat plume, the hot and humid air being shunted to the east at the end of
19:49Saturday.
19:50It doesn't go that far.
19:52It stays close by.
19:54And just to give you an example of the effect that has on these different computer model runs.
20:01Let's skip ahead to bank holiday Monday.
20:05And if I put on member number one from the European model, you can see a temperature there in the
20:11southeast of 26 Celsius.
20:14But skipping to member 11, it's 16 Celsius.
20:1921, it's 30 Celsius.
20:2231, it's 23 Celsius.
20:25Big variations in temperature.
20:27But not massive variations in terms of the overall outlook for Monday.
20:32Mostly, despite the variation in temperatures, we've got high pressure near the UK.
20:38A lot of fine weather.
20:40Now, member 11, where we've got 16 Celsius, there is lower pressure over the continent.
20:45And the potential for some showers to affect the south of the UK.
20:50But otherwise, mostly it's high pressure.
20:52And it's just the varying positions of these high pressure systems
20:55that make the difference in terms of whether the hot plume returns from the south
21:02and introduces higher temperatures and or an increased threat of showers and thunderstorms
21:08or whether it stays away and it's just mostly fine with temperatures a little bit down compared with Saturday.
21:14But otherwise, a lot of dry and sunny weather.
21:16So, those are the uncertainties we're dealing with by the time we get to Sunday and Monday.
21:21Big variations in temperatures depending on whether the plume to the south and the east returns or not.
21:29But despite all this talk of differences in temperatures,
21:33worth emphasising that it's high pressure that will be close to the UK.
21:35Many parts of the country this Monday experiencing a lot of fine weather.
21:42And compared with May so far, well, we can't really be too disappointed with that.
21:48Of course, we need the rain in some parts of the east and the southeast.
21:52And there may be some of that to come for the second half of the half-term week.
21:58But for now, we're seeing drier, sunnier and much warmer weather arriving just in time for this bank holiday weekend.
22:07So, if you've got outdoor plans, make the most of the forecast and the fine weather.
22:12And if you need that day-to-day detail, if you need to know whether it's going to be showers
22:16where you are through Saturday
22:18and perhaps into bank holiday Monday, we'll keep you updated right here.
22:23We've got you covered on the Met Office YouTube channel.
22:26Thank you for watching. Bye-bye.
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