- 2 days ago
This is an in-depth Met Office UK Weather forecast for the next week and beyond. Aidan talks to Deputy Chief Meteorologist Dan Holley about last weekend's storms. Are there more to come? Or will the jet stream keep things cool and changeable? Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
You may also enjoy:
– 10 Day trend forecast https://www.youtube.com/playlist?list=PLGVVqeJodR_ZDSHKqsgszMnk9d5IEF5UH
– Podcasts exploring weather and climate https://www.youtube.com/playlist?list=PLGVVqeJodR_brL5mcfsqI4cu42ueHttv0
– Daily weather forecasts https://www.youtube.com/playlist?list=PLGVVqeJodR_Zew9xGAqYVtGjYHau-E2yL
You may also enjoy:
– 10 Day trend forecast https://www.youtube.com/playlist?list=PLGVVqeJodR_ZDSHKqsgszMnk9d5IEF5UH
– Podcasts exploring weather and climate https://www.youtube.com/playlist?list=PLGVVqeJodR_brL5mcfsqI4cu42ueHttv0
– Daily weather forecasts https://www.youtube.com/playlist?list=PLGVVqeJodR_Zew9xGAqYVtGjYHau-E2yL
Category
🗞
NewsTranscript
00:00The jet stream has returned to the UK's shores, but why now? How long will it continue to stray close to the UK?
00:09And why does it mean different things for different people?
00:13I'll be talking about all of that in this week's Met Office Deep Dive.
00:17Hello, I'm Met Office meteorologist and weather presenter Aidan McGiven.
00:21We do these in-depth discussions of the UK's weather and beyond every Tuesday.
00:26If you're a fan of these, don't forget to tell your friends about them and subscribe as well so you never miss one of these updates.
00:33So I'm going to be talking about heat waves around the world this week.
00:36I'm going to be talking about how high temperatures could climb in the UK early next week.
00:43And I'll be talking about some very changeable weather we can expect over the next few days.
00:47But before all of that, earlier on today, I had a really interesting discussion with Deputy Chief Meteorologist Dan Holley all about the thunderstorms that we saw over the weekend.
00:59I'm joined now by Dan Holley, who is now becoming a regular and much appreciated guest on the Deep Dive since Dan moved to the Met Office following time as, well, BBC Look East's presenter amongst many other things.
01:16You might remember Dan from BBC Look East.
01:19Mention that because your old workplace was flooded in a previous batch of thunderstorms, wasn't it?
01:24Yeah, we had a round of storms that went up across Kent and East Anglia Friday week before and caused some flooding in the studio.
01:31And so that was out of action for a fair few days, actually.
01:34But thankfully, it's all back up and running now.
01:36Yeah, that was one batch of thunderstorms that we had a couple of weeks ago.
01:40We're not here to talk about that.
01:42We're talking about the batch of thunderstorms that we saw in this area, northern England, southern Scotland in particular, during the summer solstice and overnight into Sunday the 22nd of June.
01:52And one of the reasons that Dan is here is because Dan is particularly an expert at supercell thunderstorms.
02:01So we're going to be touching on supercell thunderstorms.
02:04Before we talk about the setup that we had at the weekend, I wanted to show some very impressive pictures that Dan took on a recent trip to the US.
02:15Talk us through this one first, Dan.
02:16Yeah, so this was taken about three weeks ago, back in early June, in eastern New Mexico.
02:22And what we're looking at here is a supercell, as you've already mentioned.
02:26But, you know, for me, this is probably the best structure I've seen.
02:29I've been storm chasing in the US quite a few times.
02:31And when we saw this enhanced, obviously, by the time of day with the sun setting and the oranges you get there, it just looked incredible to see firsthand and even in pictures afterwards.
02:41But it's a nice example of the kind of dynamics at play here.
02:44You've got the updraft region, so where the warm, humid air has been pulled upwards into the storm on the left-hand side.
02:50You can tell the storm is rotating, which is what a supercell is.
02:53It has a rotating mesocyclone.
02:55The updraft is rotating.
02:56Yeah.
02:56By the fact that you've got this sort of curvature going on here and you get lots of different levels to this.
03:01And then over here, you've got the downdraft, so the rain and hail coming out of the storm, lightning, obviously, you can see there as well.
03:07So what this shows nicely is the fact that the updraft region is separate from the downdraft region.
03:13And that's the key part of supercells.
03:15They have this separate updraft and downdraft because of the windshed, which we can touch on in a moment.
03:20And that allows them to last for many hours.
03:22If they remain discreet and on their own and not impeded by other storms, then they can produce all sorts of hazards.
03:28Yeah.
03:28And single-cell thunderstorms, as you were alluding to there, they have updrafts.
03:36It can be quite powerful updrafts, but they have updrafts that then with the single-cell thunderstorm, it doesn't have much of a change in wind with direction.
03:44And so the updraft goes up, downdraft comes down, and within an hour or so, kills off the updraft.
03:50So the important thing, as you were saying there, is that you've got a separate updraft, downdraft, makes it last for hours and produces much more energy, more impacts as well.
04:00Yes.
04:00And that rotation can also result in things like this.
04:06Yeah, that's right.
04:07So this was on the same day.
04:09This was actually from a different supercell that day.
04:12But you can see the size of hail you can get out of these storms.
04:15If they've got enough energy and they last long enough to sustain themselves, you can get some pretty big hail.
04:19Just for comparison, this is an American quarter coin.
04:22It's roughly two and a half centimetres in diameter.
04:25So some of these pieces of hail are larger than three centimetres here.
04:29This was on a separate day, but same idea, rotating supercell thunderstorm.
04:33And if the rotation is strong enough, especially in the low levels, then they can produce tornadoes, which can be quite strong where they do occur.
04:39So you're looking for rotation.
04:41You're looking for the energy that's available in the atmosphere.
04:44And we've got a great schematic here, actually from Jersey, from Storm Chiron.
04:51I don't know if you remember Storm Chiron.
04:52Really powerful storm, a windstorm, a low pressure system that's crossed the channel a couple of years ago, was it?
05:01Yeah, early November 2023, I think.
05:03Yeah, and it ended up producing, not only did it produce damaging wind gusts by itself, but it produced a supercell thunderstorm within it as well.
05:11And that's the structure we're seeing here, isn't it?
05:14Yeah, I mean, the probability of Jersey being impacted by a tornadic supercell is incredibly small.
05:20So it's just very unfortunate that it went across the island that night.
05:22But yeah, what you would normally expect when you're looking at radar presentation, so reflectivity on radar, is this general shape that you see by the grey shading here.
05:31So you've got this area of precipitation, rain and hail.
05:34This is the forward flank downdraft.
05:36Very strong winds, in this case from the southwest, pushing that well ahead of the storm.
05:40So this is sort of why you get the anvil pushing well ahead of the storm here.
05:43And then you get this hook feature down here, which is where the rear flank downdraft wraps around.
05:49And it's in this portion here where you've got your inflow, so that warm, moist air feeding in, being pulled upwards into the storm, helping to generate the big hail.
05:57Because obviously the stronger the updraft, the bigger the hail you can get.
06:00And it's in this hook.
06:01So quite often meteorologists are looking for these hook-like signatures where you get this enhanced spin, which can work its way down to the ground.
06:07And if that's the case, you can get a tornado, which is what this red shading here is.
06:11That's the track of the damage from a tornado, which roughly is separate from the track that we saw, all the large hails.
06:17All of these circles here, these are hail reports correlated by size.
06:22And you can see some of the hail in this event was sort of six, seven centimetres in diameter in November.
06:27So, you know, it's not just the summer you can get these big storms.
06:30It's astonishing.
06:30Yeah.
06:31Yeah.
06:31And there's the tornado damage.
06:33There was damage, significant damage from this tornado, wasn't there?
06:36And people reporting really scary moments with the incredible sound coming through.
06:43Where would you want to be as a storm chaser?
06:46Obviously, most people, most normal people want to avoid tornadoes.
06:50But someone who's experienced, like Dan, knows how to approach these storms safely to get some amazing shots like the ones you got from the U.S.
06:58Where would you approach the storm to get some shots of a tornado?
07:01So most chasers will want to be on, if it's in this situation where the storm is moving northeastwards, they'd want to be on the southeast side with a clear view of the rain-free base.
07:11Not all storms produce tornadoes, I should say.
07:13You know, only a handful of supercells in the grand scheme of things actually go on to produce tornadoes.
07:18But if that's what you're looking for, then you'd want to be on the southeast side with good road options so you can get out of its path.
07:25Because supercells don't move in a straight line.
07:27They're very finely balanced with all the forces around them.
07:30And they wobble around quite a bit.
07:31They can deviate to the right or sometimes to the left of the mean steering flow.
07:35So you've got to, you know, bear that one in mind if you're, you know, around a very powerful supercell.
07:40If you're looking for large hail, then, you know, you'd want to be in probably the forward flank downdraft.
07:45But obviously I wouldn't advise that because your car could experience quite a bit of damage if you do do that.
07:50Yeah, and the visibility would be poor there as well.
07:54So you're more at risk of a tornado coming out of nowhere.
07:57Whereas here you've got the clearer visibility.
08:00You can see the storm from a distance.
08:03Now, you're so experienced at looking at these storms in the U.S., where, of course, we do get these enormous supercells.
08:11You were on shift last Thursday and you were telling us that the setup was similar to what we get in the U.S.
08:19Yeah, so when we're looking at forecasts for thunderstorms in the U.K., very rarely do we get this overlap of a lot of instability and a lot of wind shear.
08:30But, yeah, last week we were looking at things on Thursday, for example, and there were growing signs in the models for the midweek period that we would see some thunderstorms on Saturday.
08:39And what was particularly interesting, as I say, is that overlap of strong wind shear and strong instability.
08:43Now, we get a lot of wind shear in the cooler season, autumn and winter, because the jet stream is very strong and it's often overhead.
08:49And wind shear is obviously driven by changes in wind speed or direction with height.
08:54So if you've got very strong winds aloft and not as strong winds at the surface, that's going to give you strong wind shear.
08:59But it's, for the U.K., not very common to get strong wind shear in the summer, because usually the jet's weaker or it's further north.
09:05And certainly, if we're talking about big instability, which is driven by usually high surface temperatures, usually that's under a very quiet pattern, which is hot and sunny for the most part.
09:15So to get the two combining is quite reasonably rare in the U.K.
09:19But we can see evidence of that strong wind shear in this forecast tephogram here.
09:23Obviously, this is a plot of temperature, which is the solid black line and dew point as you go up through the atmosphere.
09:28But the winds here on the right hand side give an indication.
09:31So we've got more of a southerly wind at the surface.
09:33And then as you go up through the atmosphere, it turns more to the southwest.
09:36It also gets stronger.
09:37And so it's that change in speed and direction with height, with those high temperatures we saw on Saturday, that gave us cause for concern for some quite nasty thunderstorms potentially later on in the day.
09:47So you've got the two really important ingredients there.
09:49You've got the high energy because of the high temperatures and humidity towards the surface.
09:54And then you've got that potential for strong updrafts.
09:57But they're not going to stay in the same place as the downdrafts because the whole thing is potentially rotating.
10:04But it was really finely balanced, wasn't it, because of what was going on during the afternoon.
10:09Actually, let's show a satellite sequence of what was going on because that's really important.
10:15As we went into Saturday, zoom in a little bit.
10:19This was at 10 a.m. and had some cloud moving in, didn't we?
10:24Medium level cloud.
10:26Yeah.
10:26So a lot of this cloud was driven by what we call elevated convection.
10:29And these are essentially thunderstorms that are driven by a warm layer that's in the mid-levels, so above the ground.
10:37So you can get thunderstorms where it's relatively cold to us, but the weather doesn't really care how it feels as such.
10:44It cares about differences in temperature with height.
10:46So if you've got a warm layer about a mile above the ground and there's some cold air above that, that's still unstable.
10:52And you can get these elevated showers and thunderstorms.
10:55As you can see on the radar, as you put up here, you know, a lot of precip showing up.
10:59Now, not all of this will have been reaching the ground, and we can see that in the tephograms in a moment.
11:03But, yeah, a lot of cloud across the U.K. on Saturday, which generally suppressed temperatures a little bit.
11:09We still obviously reached 33 in Surrey, where we had some longer, sunnier spells down in the southeast.
11:14But places like northeast Wales, northwest England, where we could have got into the low 30s, we didn't quite get there because of this rather extensive early convection, which wasn't particularly severe.
11:25And that lowered the threats of some quite nasty storms, at least in that part of the U.K. during the sort of late afternoon and evening hours.
11:32And we had a yellow warning, didn't we, for parts of northern England, was it into parts of Wales?
11:38Yeah, the far northeast.
11:39Yeah, into parts of southern Scotland.
11:42And that yellow warning talks about a low probability of medium-level impacts.
11:48Yes.
11:48And that's because of all these different factors that are competing.
11:52You've got the ideal ingredients, on the one hand, the powerful updrafts and the rotation potential.
12:00But you needed that energy to be released, and you needed the temperatures to rise at the surface.
12:05And those temperatures were inhibited by the earlier arrival of the cloud and the showers.
12:12So what we were going to do here is to show two scenarios, either of which could have happened, only one ended up happening.
12:22So this is the first scenario, isn't it?
12:23Yeah, so as this says up here, 18z, so that's 7pm over northwest England.
12:28And I've modified this profile to kind of give an indication of what could have happened if temperatures were high enough in this part of the world.
12:35And you can see lots of instability.
12:37So this red shading here is what we call CAPE, or convective available potential energy.
12:42And this is of the order of 1,500 joules per kilogram.
12:47So, you know, fairly decent CAPE for UK standards.
12:49In the US, they probably wouldn't, you know, bother too much about that amount of CAPE, but for the UK, it's pretty good going.
12:55And again, you can see that strong wind shear.
12:57So south-south-east winds at the surface, south-westerly aloft, and they increase with height.
13:00So, you know, decent CAPE, strong wind shear, could have generated some pretty nasty thunderstorms.
13:06Now, when it comes to tornado potential, you need these supercells to really be interacting with what we call the boundary layer.
13:12So the lowest part of the atmosphere near the ground, because that's where the strongest turning with height of these winds was on Saturday.
13:19Yeah.
13:19As it transpired, we didn't really see a huge amount of surface-based convection, because temperatures didn't quite get high enough.
13:26So the convection that happened later in the day, being elevated in nature, driven by warm air higher up, wasn't able then to tap into that really strong shear down at low levels.
13:35So as far as I'm aware, we haven't seen much in the way of tornado reports, but we have seen some pretty big hail from the storms later in the day.
13:41Yeah, because we still had this second scenario, and this is the one that played out, isn't it?
13:46We didn't quite get the temperatures at the surface, but we still had that strong instability, all that energy available higher up in the atmosphere.
13:53Yeah, so this is a profile a bit further north, up towards sort of Cumberland or Thumberland Way, at around 11pm.
13:59And you can see by this stage, this solid black line here, which is our temperature traced with height, has started to cool off at the surface, which is common in the evening as temperatures start to fall away.
14:08So we're no longer going to get surface-based convection at that point, because we've got this warm nose aloft, which sort of acts as a cap.
14:15But we still have plenty of instability from these layers higher up above the ground.
14:20As you can see, still plenty of capes showing up on this diagram, and still plenty of shear.
14:24So the ingredients were still there for some pretty nasty thunderstorms, but we could have seen even more further south earlier in the day, had we just had a bit more heating in the afternoon.
14:33Just goes to show how finely balanced these things are.
14:36And another thing to bear in mind is how localised they can be as well.
14:41Looking at the radar here, we're going to talk about two different types of radar.
14:45One thing to note is that some places didn't get much at all, even if you're in the warning area.
14:49Of course, we always emphasise that in our forecast, that some areas won't get everything coming together in the right way.
14:55And of course, if you get some significant thunderstorms in one location, they can inhibit the development of thunderstorms in another location.
15:01So it's so finely balanced, but we've got two radars here, a more typical radar that we're used to seeing on top, which we can look at now.
15:09And then a Doppler radar on the bottom, which we can explain what's going on there.
15:13So this is half past 11?
15:17Yes.
15:18Yeah.
15:18So this is what we call single-sight radar.
15:21Usually we look at a composite, which is lots of different radars all merged together over the UK.
15:25So the radar is based here where there's little white crosses.
15:28And what we see here, ignore a lot of this, this is sort of general clutter in the radar, things like hills and wind turbines and stuff like that.
15:36What we're looking at over here are the big storms that developed over Cumbria into western Northumberland.
15:40And these two cells in particular, thinking back to the schematic we looked at earlier from Jersey, we can see that same sort of shape being revealed here in the radar signatures just from the reflectivity, so just from the precipitation signature.
15:54And that's why, burrowing into some of the other data we can get from the radar, we start to get some more interesting features coming through.
16:00And you look at this, don't you?
16:02This is Doppler radar.
16:03Can you explain how this works?
16:04Yeah, so this is looking at what the winds are doing, which is quite handy, especially in these sorts of situations.
16:11So there's a lot of noise on here, so ignore that.
16:14But what we're looking at are these red and green shaded areas over here in particular.
16:18So where we see this red shading, this is where the radar is picking up winds or particles moving away from the radar.
16:25The radar site, of course, is down here.
16:27So this would indicate some sort of southeasterly component to the wind.
16:30Where we see the green shading, that's the opposite.
16:32The winds are sort of flowing towards the radar, so some sort of westerly component.
16:37And where the two meet, that's indicative of rotation, essentially, especially where they start to get really bright colours, the stronger flow.
16:45And we see these two couplets here, which I've put in these two white circles, which correlate with the position of those reflectivity echoes we just saw.
16:54So this is quite a strong indicator that we had rotation in those thunderstorms.
16:57In other words, they were supercells.
16:59But also worth bearing in mind, we're quite far away from the radar site, so the beam gets higher the further away you go from the radar.
17:04So we're sampling these in sort of the mid-levels rather than down at the surface.
17:08Yeah.
17:09And that kind of rotation, that kind of storm can produce considerable impacts, which you were warning of on Thursday.
17:17Remember your forecast on Thursday, we were talking about large hail.
17:19What are we looking at in this image here?
17:22Yeah.
17:22So later last week, we were talking about the potential for two to four centimetre size hail in some of the most impactful storms.
17:28This product over here from the radar is trying to estimate the maximum hail size we could theoretically get from that storm.
17:36And you can see there are various storms here, which suggests with the key down here, sort of one to two centimetre hail.
17:41But this particular storm that crossed out of Cumbria across the fells into Northumberland is being picked up as potentially having four centimetre diameter hail in it.
17:50Now, the only issue with that, with that being able to verify it, is the fact that it's over a pretty rural area with no one around.
17:57So we're none the wiser whether actually four centimetre hail came out of this storm because, you know, there isn't anyone really there to report it.
18:04And obviously, it's in the middle of the night as well.
18:06So, as I say, we don't really know whether we got four centimetre hail from this.
18:10But we certainly got reports of two centimetre hail from parts of south-east Scotland where these storms kept running over the same area.
18:16And people talked about thunderstorms occurring for several hours, didn't they?
18:19Yeah. Yeah. So underneath this line, we saw numerous cells.
18:24You can see the two supercells here. There may have been others earlier on in the sequence.
18:28But, you know, numerous storms running along this same line up across similar areas, Cumbria and Northumberland into south-east Scotland.
18:34Some places had more than 40 millimetres of rain.
18:36And we did see a little bit of flooding in some places as well.
18:38Yeah. So pretty big impacts.
18:41There was a yellow warning, of course.
18:43It could have been escalated to an amber had those temperatures been realised at the surface.
18:49And, you know, we had a lucky escape.
18:52People of northern England, southern Scotland had a lucky escape in many ways because those really powerful storms didn't quite materialise.
19:00But we certainly saw plenty of impacts from the rain and the hail and the frequent lightning as well.
19:06But of course, as is always the case, and we always emphasise this in our forecast, not everywhere in the warning area is going to experience these storms.
19:14You know, no matter how much the ingredients can come together in these locations, they just don't happen in that way, do they?
19:21No, that's right. And even outside of the precipitation, you could be somewhere over here and seeing this constant flashing of lightning to the north, but not getting any rain, you know, where you are.
19:31And I just want to end on this, because this is spectacular, isn't it?
19:34From Philip Cadwallader.
19:35Yeah, so this was taken in Darlington a little bit earlier on in the evening.
19:39And, you know, I saw this on social media and I thought that actually looks, you know, visually like a supercell.
19:45You can see it's similar to the pictures we were looking at earlier with that curvature going on here.
19:49Fairly high-based.
19:51But, yeah, so, you know, if nothing else, we've got radar evidence, but we've also got some ground evidence from the photos that we did see potentially some supercells on Saturday evening.
20:00Darlington, well, it could be, bring us back full circle, New Mexico.
20:05It could have been, yes.
20:06Yeah, which is exactly what you were talking about on Thursday when you were talking about all those ingredients potentially coming together for the weekend.
20:12Yeah.
20:12Dan, thank you very much for coming on the Deep Dive and sharing the imagery and your expertise with us. Much appreciated.
20:19That's been a pleasure. Thank you.
20:21Thanks again to Dan Holley for that really interesting discussion.
20:24Dan had to rush off to another appointment when we recorded this earlier in the day,
20:28but he's so conscientious that he messaged me later to say that he forgot to mention a couple of small details
20:34that were really interesting, actually, in terms of how these thunderstorms developed and why they occurred where they occurred.
20:42And we've got two images here that show two different aspects of the atmosphere that basically coincided to decide where those thunderstorms were occurring.
20:51One, the image on the top, is the water vapour when you're looking down from high up.
20:56So it's the water vapour in the atmosphere and where you've got dark areas occurring, that's where there is less water vapour.
21:04So it's indicative of what we might call a dry slot.
21:07And this dry slot of the atmosphere coming in, way up high in the atmosphere, coming into north-west England, south-west Scotland there on Saturday.
21:17But that coincides, that overruns an area of warmer and moist air at lower levels, although still relatively high up.
21:25This shows what we call the wet bulb potential temperature at 700 hectopascals.
21:30700 hectopascals is what we call the slice of atmosphere that typically lies at around 3,000 metres or 10,000 feet high in the sky.
21:42So this is a slice of atmosphere and it's showing the temperature and the humidity at that level.
21:49So it's the redder, orangey colours show where it's particularly warm and humid at three kilometres above the ground, basically.
21:59And that high humidity, high temperature air at that height is sitting over parts of Wales, north-west England and south-west Scotland.
22:08But what this suggests is that higher up than that, we've got this area of cooler, drier atmosphere that is running in over the top.
22:17And, of course, that then increases the instability at those higher levels in the atmosphere.
22:23So, where you've got the cool, dry zone running in over the top of the warm, moist zone at 3,000 metres, then it causes enhanced instability.
22:35And that's why this particular location, where you've got the very warm, moist air at 3,000 metres, 10,000 feet, sits below the cooler, drier air, even higher up.
22:45But that's why we saw those thunderstorms breaking out across parts of north-west England into southern Scotland.
22:52So Dan could explain it much better than I could, but hopefully that has covered that.
22:56He also wants me to mention the reason why we saw a lot of rain on the radar earlier in the day on Saturday, but not much of that rain has reached the ground.
23:06And it's basically because we had a lot of dry air towards the surface, and so a lot of that rain was evaporating.
23:11It was being captured by the radar, but by the time it reached the ground, it was evaporating.
23:16And, yeah, I experienced it myself in Devon.
23:18We had these very large drops of water coming down, not many of them, very large drops.
23:24On Saturday afternoon, I was at the dog show, and my daughter's won first prize for the best junior handler, by the way.
23:33But during that dog show, these big drops of water came down.
23:37I checked the radar, looked very angry on the radar, but it was nowhere near as heavy as that in reality.
23:43Now, moving on to something that is very related in terms of thunderstorm development, but in a different location.
23:51I want to look at the potential for thunderstorms on Wednesday evening.
23:55And we've got a similar setup, but, as I say, in a different location compared with over the weekend,
24:01which, of course, was centred over parts of northern England and southern Scotland.
24:06This is Wednesday morning, and what you can see here is the jet stream starting to move over the North Atlantic.
24:14And over the UK, it's a mostly fine day with a ridge of higher pressure there,
24:18with a ridge coming up from the south, a weather front sitting, but decaying over central parts of the UK.
24:24But meanwhile, there's another filament of the jet stream that's just cut off from the main flow that's sitting over Iberia.
24:31So there's this circulation way up high in the atmosphere, and that's causing a lot of instability,
24:37because where you've got this area of low pressure way up high in the atmosphere, it creates a vacuum.
24:41You've got this rising air, so you've got all this rising air over Iberia.
24:44And then through Wednesday, that area starts to move northeastwards into France.
24:52If I put the rainfall forecast there, then you can see some of these heavy showers breaking out
24:57mid-afternoon across parts of France into northern Spain, as well as perhaps Portugal.
25:04The whole thing by the evening is progressing northeastwards.
25:09And there's a few things going on that relate to our discussion with Dan earlier.
25:16We've got the upper area of low pressure, so we've got rising air from the surface, as well as some wind shear.
25:22So that difference in wind speed and direction with height, lighter surface winds, but then as you go up through the atmosphere,
25:28you meet those stronger winds because of the jet stream.
25:30And a change in wind direction, as well, with the jet stream further out in the Atlantic wanting to bring in cooler air.
25:38You've also got relatively high temperatures over the near continent and just fringing into the southeast of England.
25:47So with those relatively high temperatures, high humidities, and the change in wind direction with height,
25:55we've got a lot of available energy and the potential for some of these severe thunderstorms to break out.
26:01And if I just show you this graphic here, which is the forecast CAPE.
26:07Dan mentioned CAPE. It's basically a measure of the amount of available energy in the atmosphere as a result of those temperature differences
26:15and the rising air as you go from the surface higher up in the atmosphere.
26:21And there's all these bright colours across the near continent there.
26:24And so that indicates the potential there. Lots of energy over the continent.
26:28And as you get that filament of the jet stream moving in, you've got the rising air.
26:33You've got a lot of potential for some severe thunderstorms to break out.
26:38But the edge of that higher energy potential is just staying on the continent.
26:44And there are a lot of uncertainties about the extent to which those thunderstorms will fringe upon the far southeast of England.
26:52Meanwhile, there will be some other showers drifting north across other parts of the UK.
26:56Basically, the southeastern half there of the UK, if you were to have a dividing line somewhere from Lime Bay up towards parts of northeast England,
27:06it's that southeastern half where we could see some showers drifting north later Wednesday and into the early hours of Thursday.
27:13But for the proper thunderstorms, including frequent lightning, large hail, gusty winds, torrential rain,
27:21they're mostly going to be breaking out over the near continent.
27:24But there is that risk that they'll just brush past the far southeast of England, particularly Kent.
27:31So it's one of those situations that is finely balanced depending on the track of these storms as they develop later Wednesday and through the early hours of Thursday,
27:39whether they precisely hit the UK land area or whether they just stay to the east.
27:46But it is the far southeast at greater risk of that.
27:50And of course, we keep updated on the details of that.
27:54I mean, the computer moles, if we go to Wednesday, you can just keep I wouldn't take this too literally because, as I mentioned,
28:02there are uncertainties over the track of these.
28:04And often we don't have a full confidence in where they're going until they start developing.
28:09But you can see here some angry looking blobs of rain then start drifting north.
28:17So that just shows how it may well play out across southeastern parts of the UK.
28:21This is heading towards midnight on Wednesday and going into Thursday before they clear away.
28:27Meanwhile, ahead of that, we've also got the potential for some other showers across parts of England and Wales, for example, as we end Wednesday.
28:35But Wednesday itself, before all of that happens, mostly dry day, a few showers here and there, some sunny spells, but a lot of cloudier areas drifting around.
28:44And as I mentioned, that hotter air that we've got over the near continents, the more humid air, it will make some inroads into the south of the UK,
28:52even if northern parts of the UK stay cooler with temperatures closer to average.
28:57And there is a heat wave ongoing across parts of Europe at the moment.
29:00So we can take a look at the temperatures that we can expect over the next few days.
29:06In fact, I need the touchscreen pen for this to draw some temperatures on.
29:12And if we skip ahead to Wednesday, what we can see there is 28 Celsius for London.
29:19That seems like a most likely temperature for the southeast.
29:2222 for Dublin there, if we put a few more temperatures on there.
29:25Nothing particularly outstanding for, I think I captured a mountaintop there across northwest Scotland.
29:32That's why the 8s and 9s are coming up.
29:34But more likely the mid to high teens across Scotland, low 20s across northern and western parts of the UK.
29:39It's really that southeast corner where we're getting to the mid to high 20s in places.
29:45So, yeah, not as hot as it was on Saturday when we had 33 Celsius in Surrey,
29:51but still hotter and more humid because we're just getting into the edge of this heat wave
29:57that is across southern, central and eastern parts of Europe.
30:04The heat, of course, that we had at the weekend that has been brushed to the east and southeast.
30:08And over the next few days, we can expect temperatures to rise quite significantly across this part of Europe.
30:16We're talking about the Balearics into Corsica and Sardinia, Italy.
30:20And if we go forward to Thursday, you can see the temperatures are increasing across parts of southeastern Europe, especially.
30:29Friday, then, the heat starts to build once again across Spain and Portugal.
30:35So, yeah, there's always the potential for all this hot air to the south of the UK.
30:41And it will occasionally fringe upon the south and southeast.
30:45And I'll talk more about temperatures early next week in the southeast in a moment.
30:49But for now, really, certainly through Wednesday, we're on the edge of that heat.
30:55And it's along that edge where we're likely to see those showers and thunderstorms breaking out.
31:02Meanwhile, it's not just Europe where we're seeing very high temperatures.
31:08If we go back to Tuesday, so the time of recording.
31:10Now, I'm recording this at 1 o'clock, and so it's 8 a.m. across northeastern parts of the U.S.
31:20And already it's 32 Celsius at 8 a.m.
31:23JFK Airport, Newark Airport as well, 32 Celsius.
31:28And it looks likely that New York, this is New York here, will see a temperature of 38 Celsius during Tuesday.
31:35It could even exceed 38 Celsius.
31:37New York's June record is 38 Celsius.
31:41And we're likely to see temperatures in some parts of this region.
31:45I don't know if it's the right spot there.
31:47We've got a 39 there.
31:48Just saw it at the corner of my eye.
31:50So mid to high 30s widely, perhaps 40 Celsius.
31:53So these are locally, at least, some record-breaking temperatures from northeastern parts of the U.S.
32:00The heat wave peaks on Tuesday before gradually easing over the next few days.
32:06As you can see, it's still staying hot.
32:07But, you know, we're seeing temperatures climb back to the low 30s or high 20s more widely.
32:13Why is it so hot across North America?
32:16Well, actually, let's switch to this view.
32:18It will help to explain things because we've got the jet stream here.
32:23And what you can see from the jet stream is this big dip over the Rockies.
32:31And so the jet stream becoming more amplified.
32:33It's diving south over the Rockies.
32:35Then it rises high over northeastern USA.
32:40And as a result, what we've seen over the last few days is hot and humid air over the Gulf of Mexico being drawn northwards.
32:48And this big plume of hot and humid air pushing northwards into northeastern parts of the USA.
32:54Now, this isn't just relevant in terms of North America.
32:58It's also relevant for ourselves because it will have an effect on our own weather, as is often the case when you get these big contrasts over North America.
33:07It can cause a more powerful jet stream.
33:10Let's take a look at the temperatures on the jet stream.
33:14Turn off the jet stream there.
33:16And so the temperatures across North America, we've got this cool air, this cool air here, hot air over here, and in between, a more powerful jet stream develops.
33:30And that is indeed what we're seeing.
33:33And it's this.
33:35Oh, I can't get that off now.
33:37Hang on.
33:37Let's turn that off.
33:38OK.
33:38It's this part of the jet stream over North America that ultimately starts to come our way.
33:44So if we skip forward to Wednesday, you can see that powerful streak in the jet stream relatively in a flat position starting to make its way across the Atlantic.
33:57And it's that streak, that flat streak in the jet stream that will eventually, during Thursday and into Friday, impact the UK's weather.
34:08And as a result, we're going to see very changeable weather across the UK, but big differences depending on where you are.
34:16And as you can see, you've got low pressure that's pushing through Iceland, higher pressure over the Azores extending into Iberia.
34:23It's in these kinds of setups that you get big differences between the cool air to the north, so this area is cool, and the very warm air to the south.
34:37And initially, because of those big differences, you get areas of cloud and outbreaks of rain along what's called a warm conveyor pushing into the UK.
34:48And where those clouds and outbreaks of rain push into higher parts of west and northwest UK, you get rather a lot of rainfall in the north and west, breezy conditions, and some quite strong winds, actually,
35:01because of the jet stream helping to deepen these areas of low pressure, so some quite strong winds across the north and northwest.
35:07Meanwhile, because of these westerlies dumping a lot of the rainfall across western hills, it's going to be relatively dry towards the south and the southeast,
35:16notwithstanding the potential for those thunderstorms that I mentioned on Wednesday night, which could bring a lot of rainfall.
35:22And with this setup and the increased temperature differences and pressure differences across western Europe,
35:29you can get the heat building across Spain, Portugal.
35:34And so, eventually, with hot air building here, if the jet stream, and this is what I'm going to mention in a moment or so,
35:40if the jet stream then just points in a slightly different position, then the UK is primed to see some of that warmth arrive in the south and southeast.
35:52So, yeah, over the next few days, the weather's turning more changeable.
35:55The jet stream in charge setting up this conveyor that initially brings some wet weather later Thursday and into Friday.
36:06Actually, if I play this forward, you can see how this is the rolling rainfall totals.
36:12So, between now and Thursday, you can see how some of these darker blues are indicating 25 millimetres of rainfall across parts of Cumbria and to western Scotland.
36:24If we skip forward to Friday, there are some spots showing 50 millimetres or more across Cumbria and western Scotland.
36:32But equally, these white areas and certainly the lightest blue colour indicates very dry weather continuing across parts of eastern England.
36:41But some of the darker spots there showing up across just the east of London, east Anglia and the southeast because of the potential for those thunderstorms.
36:50But, of course, with the uncertainty over the track, I wouldn't take that too literally.
36:54So, that west-east contrast enhanced during Thursday and Friday as we see spells of rain move in because of the westward jet stream that's coming in from the Atlantic.
37:11So, wet picture basically across northwest England, western Scotland, but drier towards the southeast.
37:17And the winds are potentially going to be very strong as well.
37:24Not unusually strong, but, yeah, let's pick up the winds.
37:30It's going to be a breezy few days, certainly later Thursday and into Friday.
37:35Just the hint there of 50 miles an hour, that's what these colours are showing across western and northern parts of Scotland.
37:41So, approaching 50 miles an hour for some exposed northern and western coasts of the UK.
37:45Blustery for many of us in the north and the west during Thursday and Friday.
37:51A little bit blustery for Glastonbury for the set-up before those winds ease later Friday and into the weekend.
37:58And we're going to see that jet stream continue to stay with us as we start the weekend, enhancing those north-south differences.
38:08So, here's how Saturday looks.
38:13We've got, let's move it back a few frames.
38:17That's not working.
38:18There we go.
38:21We've got a weather front moving south, becoming detached from the jet stream, which is starting to push north.
38:27That weather front then fizzles away.
38:30Brighter skies follow with some cooler air across northern parts of the UK.
38:35But by the time we get to Sunday, the jet stream is beginning to push north again and higher pressure is beginning to move up north again.
38:44And as I mentioned, when you've got that strong west to east jet stream lying across the Atlantic, you can see the heat build up over Iberia, whilst it stays very cool across northern parts of the UK.
38:55But then if the jet stream then starts to build north again and you get higher pressure building up from the south, some of that heat over the continent can start to drift north as well.
39:06And so, it's going to be much more localised and less intense compared with the last hot spell that we had at the end of last week.
39:13But there's the potential, because of this new situation that evolves into Sunday and early next week, for some reasonably high temperatures in the south and southeast.
39:24Let's take a look at that.
39:25And I was just going to show you the probability of 30 Celsius to show that it's mostly confined to the southeastern quarter of the UK and certainly a much higher chance over the near continent.
39:39So, widely across many parts of England and Wales, we can expect temperatures to be, this is Monday, we can expect temperatures to be in the low to mid-20s and across southeastern areas into the high-20s, perhaps nudging up towards 30 Celsius.
39:57So, like I say, not as high as the temperatures that we saw at the start of the weekend, but still the potential for 30 Celsius there in the southeast.
40:04And again on Tuesday, just a probability there, not the strongest probability, but the signs there of 30 Celsius across parts of eastern and southeastern England.
40:18Meanwhile, Scotland, Northern Ireland, perhaps northern England, seeing temperatures closer to average, although perhaps a little bit warmer than average and certainly warmer than we're seeing over the next few days.
40:29But you can see that difference in the north-south distribution of the temperatures and the trend.
40:34If we look at a meteogram, this is for London and it shows these red boxes here.
40:39That's the range of possible temperatures each day.
40:42The days progress along the bottom here.
40:45We've got Tuesday and Monday, Monday the 30th.
40:48And you can see the boxes heading up towards the extremes for the time of year.
40:54So, that's the red line up here.
40:55Here's the average, that's the bold red line.
40:59But then, by Tuesday, the box is really big, basically indicating that there's uncertainty about how high the temperatures get on Tuesday.
41:07Could be anything from average up to well above average in London and the southeast.
41:12Before, much greater clarity for those temperatures return closer to average from Wednesday onwards.
41:18Similarly, this is for Glasgow.
41:20And it also shows a rise in temperatures through the weekend, but not as high.
41:25It doesn't quite reach the extremes that London sees.
41:28And it doesn't quite reach the extremes that we saw indicated for Friday and Saturday for parts of Scotland as we were looking at it last week.
41:36So, warmer than average spell coming up for Glasgow there.
41:40Temperatures around the low 20s.
41:42We feel those temperatures dip back down more decidedly, so from Tuesday.
41:46And essentially, what's happening is, by Tuesday, we've got a cold front moving in from the west.
41:51So, eventually, that's going to introduce cooler, fresher air.
41:55But not necessarily particularly unsettled.
41:58If I move on to this graphic here and show the most likely weather patterns.
42:06In fact, we'll change the view to the difference from average temperatures.
42:11And this is Wednesday.
42:15And it shows the top three most likely weather patterns when we run computer models many, many, many times.
42:21The most likely weather pattern is we've got this extension of the Azores high, average temperatures across the UK.
42:29That's what these colours are indicating.
42:31Broadly average temperatures across the UK.
42:33So, most places, fine.
42:34Cold front moves through.
42:36It's feeling cooler and fresher.
42:37But the Azores high, this semi-permanent area of high pressure that sits in the Azores, extends to bring mostly dry and bright weather to much of the UK.
42:46Although, potentially staying changeable in the far north and northwest.
42:50This second most likely scenario is very, very similar.
42:55High pressure to the southwest.
42:57A bit more of a cool northwest of the airflow.
42:59So, temperature's a little below average in this scenario.
43:02But most places, fine.
43:03And this is broadly similar again.
43:05Third most likely.
43:06Unbiased northwesterly, it says.
43:08So, neither low pressure nor high pressure.
43:11Northwesterly winds, temperatures back slightly below average.
43:14So, that's for the middle of next week.
43:16And really, that continues those general themes throughout much next week.
43:21This is Friday.
43:22And we've got this most likely scenario.
43:25Northwesterly breezes, but mostly fine.
43:27High pressure to the southwest.
43:28Tending to dominate, but basically it indicates that this Azores high is going to ebb and flow, extend its influence across the UK, and then retreat back to the southwest.
43:38But mostly, after that brief hot spell that I mentioned that is mostly going to be confined to the south and east of the UK, we're likely to see cooler air arrive, but still mostly settle through next week.
43:50That's what the trends are indicating now.
43:52Beyond that, very difficult to be certain at this time of year, because there aren't broad signals around the globe that we can grasp hold of.
44:02The weather patterns are much more fickle and tenuous in the middle of summer.
44:07But the computers are currently indicating that by the time we get to week three, we'll see more of a northwest of the influence and low pressure a bit closer to the UK, particularly towards the north.
44:17And that would indicate that we'll perhaps see a bit more of a pulse of the jet stream returning, having been pushed further north later next week.
44:25And allowing that Azores high to move in, it looks a bit more likely that for the weekend after next, that Azores high will retreat a little bit further towards the Azores again and allow a pulse of the jet stream to run in and bring more changeable weather to many places, particularly northern areas.
44:42But of course, it's all very far off as far as weather's concerned, and we'll be keeping you updated right here.
44:50We'll have the 10-day trend tomorrow.
44:52That will be Alex Deacon, so make sure you tune in for that.
44:55And yeah, if you like what you see here, subscribe.
44:58And oh, if you've not seen the volcanoes video that we put out at the weekend, then you might want to look up that as well.
45:07It's on our YouTube channel, how volcanoes can affect the weather and climate in the UK and around the world.
45:14So yeah, put aside some time to watch that.
45:18Enjoy, and thanks for watching.
45:19Bye-bye.
45:28Bye-bye.
Recommended
0:50
|
Up next
1:52
25:15
52:49
30:56
1:00:17