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This is an in-depth Met Office UK Weather forecast for the next week and beyond. Extreme rain is expected across parts of eastern South Asia this week ahead of the rainy season. What is causing such high moisture and instability in the atmosphere? And how’s the UK’s weather looking ahead of the Bank Holiday weekend? Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:01Extreme rain across eastern parts of South Asia and less extreme but relatively mixed weather to come for the UK
00:11this bank holiday weekend.
00:13Welcome to the Met Office Deep Dive. Thank you for joining me. It's Tuesday. We do these every Tuesday here
00:19on the Met Office YouTube channel.
00:21You can also get them on our Spotify channel and a couple of other places.
00:24So make sure you subscribe to those places so that you never miss one of these updates.
00:30And if you know someone who would love a deep dive in depth weather forecast like these, do spread the
00:39love.
00:40This week, I'm going to mostly focusing on global weather, specifically eastern parts of South Asia.
00:46I know that when we focus on global weather rather than the UK, it can divide opinion.
00:51Some people love it. Some people hate it. But hopefully this will be interesting.
00:54Not just because it's going to be so severe and potentially impactful, but because of the dynamics involved.
01:02I'm going to be looking at how the atmosphere is structured both spatially and from the bottom to the top
01:09to enable such extreme rainfall across eastern parts of South Asia.
01:16Before I get into that, where is the hottest place in the world right now?
01:25I'll tell you where. India and Pakistan.
01:30These are the top 15 hottest locations from official weather stations during the last 24 hours and typically temperatures in
01:40the mid or even high 40s.
01:42Now, I'm not suggesting that this is particularly extreme for these areas and at this time of year.
01:48But it does help to set the scene for what I'm going to go into in terms of the setup
01:55and the weather we're expecting this week across eastern parts of South Asia.
02:00Now, this is the current setup across India, Pakistan as well.
02:06I'm going to put the temperature on. You can see that heat.
02:10This is the 5000 foot temperature, but it helps to indicate where the hot air is prevalent across India and
02:19Pakistan.
02:19Again, nothing particularly unusual about this at this time of year.
02:24It is the hottest time of year for the Indian subcontinent.
02:28It is, of course, coming to the end of the dry season and eventually going into the monsoon or the
02:35rainy season.
02:37But that heat at the moment is causing what we call a heat low.
02:41The hot air at the surface rising and we get this low pressure forming through Pakistan and India.
02:50Now, that allows winds to circulate around it.
02:56And for the Bay of Bengal and into Bangladesh and north eastern parts of India, Myanmar,
03:01that very warm and very moist air is being drawn north at the moment.
03:09You can see those wind arrows drawing this tropical moisture north across this area.
03:16Not only do we have tropical moisture being drawn north because of the heat low across India and Pakistan,
03:24but we've also got a subtropical jet stream.
03:29Now, this graphic here shows the temperature at 300 hectopascals in the atmosphere.
03:34So, way up high in the atmosphere, 30,000, 40,000 feet or so.
03:40And it also shows, so these are the warmer areas and these are the colder areas at that height,
03:45but also shows the winds at that height.
03:47So, it's indicating where the jet streams and the subtropical jet stream specifically is at the moment.
03:55Now, this is Tuesday afternoon.
03:56And what you can see is the wind arrows are closer together and stronger through central India,
04:02through the Bay of Bengal there with lighter winds further north.
04:07So, we've got this peak in the jet streams, this very fast flowing stream just to the south of this
04:14region.
04:15And that causes a vacuum effect in the upper atmosphere around Bangladesh, northeast India, parts of Nepal, Myanmar.
04:26So, in this region, not only have we got at the surface this very warm, very moist southerly wind pushing
04:35northwards,
04:36we've also got a vacuum high up in the atmosphere where the jet stream is.
04:40And that causes the air to be sucked up from the ground and that low level moisture then is forced
04:48to rise.
04:49So, those are the key ingredients involved.
04:53There's another thing that I'm going to talk about in a moment called wind shear.
04:57But these are the key ingredients involved for causing heavy, prolonged, thundery rain, some intense storms over the next few
05:06days.
05:07We're talking about frequent lightning, we're talking about 25mm sized hail or more.
05:14And we're talking about really quite devastating amounts of rainfall.
05:19How much rain are we talking about for that region?
05:22Well, let's take a look at this graphic which shows rain totals.
05:28I move from the UK to the other side of the world.
05:33And this is the rolling rain total from Tuesday.
05:39Press play.
05:40And this is the region we're looking at.
05:42So, we're talking about Bangladesh, particularly towards the east of Bangladesh, northeast of Bangladesh,
05:46into the eastern Himalaya foothills as well as for parts of western and northwestern Myanmar,
05:53northeastern India and parts of the far east of Nepal.
05:57So, this area you can see, these are the rolling rain totals.
06:01So, the rain adding up through the next few days.
06:04By now we're on to Thursday.
06:05And you can see the bright colours here indicating in excess of 75mm where we've got the yellows.
06:12And I'll zoom in a touch.
06:13Got a few place names coming on there.
06:16And we've got the oranges and reds, 150, 300mm.
06:21So, this area here, 300mm of rain by Friday.
06:26And to put this into context, fairly widely in this region, 300mm is the average for the month.
06:34And in some places, you'd expect, say, for eastern parts of Nepal into some of the more hilly areas towards
06:43the north of this area,
06:44you'd expect 800 to 1,000mm in the month.
06:48But what this graphic suggests is that we're going to get similar or close to those values in the next
06:55five days.
06:56So, we're still seeing the rain increase as we go into the weekend.
07:00And these darker reds are coming through.
07:02So, that indicates more than 600mm through the next five days in this fairly large region.
07:10And two place names here indicated.
07:13Silet is in Bangladesh.
07:16Shillong is in northeast India.
07:18So, this is the area that is at highest risk.
07:21It's where the terrain starts to become more hilly as you go further north from this very flat area across
07:28parts of Bangladesh.
07:29You go further north and you get this rise in elevation.
07:32So, that's helping to enhance the rain as well as all the other atmospheric dynamics that are going on.
07:39So, this amount of rain.
07:41Not far off a month's worth of rain in the next few days.
07:45Coming in a couple of bouts of particularly intense episodes.
07:50Now, we've already seen that happen in the last 24, 36 hours.
07:55And we're going to see another peak in the rainfall later Thursday through Friday and into the start of the
08:00weekend.
08:00So, several episodes of very intense rainfall.
08:05Huge thunderstorms.
08:07And that is likely to lead to some really significant impacts for this part of the world.
08:13What are we talking about?
08:14We're talking about river flooding.
08:16Yes.
08:17Now, one saving grace is that this is right at the start of the monsoon rain period for this region.
08:25So, it's at this time of year, late April, going into May that we start to see the rains increase.
08:30In the past few years, they've had a long period of drier weather.
08:32So, that's one saving grace.
08:34It's not at the end of the monsoon rain season.
08:36It's right at the start.
08:38But river flooding still potentially an issue.
08:43More likely to cause widespread impacts and really significant impacts.
08:49There's a flash flooding of main urban areas.
08:52A lot of people live in this region.
08:55And so, thousands if not millions of people could be affected by this really severe weather over the next few
09:02days.
09:04Now, why is it so extreme?
09:07How extreme is it?
09:07First of all, let's take a look at this graphic which shows us how extreme it is.
09:12Because, like I say, it's going into a wet period for a very wet part of the world.
09:18It's one of the wettest parts of the world.
09:20And they typically get a lot of rain during this time of year.
09:26But this graphic shows the amount of rain expected over the next five days.
09:30And this graphic sums up the total rainfall between day one and day five.
09:35So, from, what day are we on?
09:37Tuesday, Wednesday, Thursday, Friday, Saturday.
09:41And, well, let's point out India is here.
09:46Here we've got Southeast Asia.
09:48And it's in the middle.
09:50There are the Himalayas.
09:52You've got Nepal through here.
09:54Bangladesh, northeastern parts of India.
09:57And these colours, where we've got the darker colours here.
10:010.8, 0.9.
10:04That's where, according to the European model, ECMWF, extreme amounts of rain are expected.
10:12So, this compares the amount of rain over the next five days with the climate.
10:17A 50-year period in which it's using as a baseline.
10:20And it's coming up with an assessment of how unusual.
10:25Anything coloured in is unusual.
10:27Anything coloured in with these darker colours, fairly extreme.
10:30And so, it's showing extreme amounts of rainfall for already a very wet part of the world in a wet
10:38period of year.
10:40Now, why is it so wet?
10:47Mostly, it's actually because of the jet stream that I mentioned.
10:52So, there's a subtropical jet stream.
10:56We, ourselves in the UK, are affected by the polar jet stream.
10:59But there's often another jet stream further south, close to the equator, called the subtropical jet stream.
11:05That tends to divide hot tropical air with less hot subtropical air.
11:10And at this time of year, yeah, you often get a subtropical jet stream that causes an enhancement of rainfall
11:17in this region.
11:18But actually, so far this week, the subtropical jet stream has been shifted further south compared with normal.
11:25That's what this graphic shows, just to point out where the key areas are.
11:28Again, there's India, there's Sri Lanka, and there's Bangladesh.
11:33So, what we are showing here, the black wind barbs, that's what they're called, are the speeds of the jet
11:41stream.
11:41So, you've got the stronger speeds going through central parts of India into the Bay of Bengal, as mentioned previously.
11:51This is a snapshot for midnight last night, by the way.
11:56The red colours indicate where the jet stream is stronger than normal.
12:02So, these are wind anomalies.
12:04Lighter winds, indicated by the blues, for North India into Nepal and Bangladesh indeed.
12:10But it's further south, where we've got this streak of strong winds, unusually south-shifted jet stream across central India
12:20through the Bay of Bengal.
12:22So, the important stuff happens to the north of the jet stream.
12:28In previous deep dives, for example, a really good one presented by Alex Deacon, we've gone into detail about why
12:37parts of the jet stream encourage uplift of air more than others.
12:45And there's a particular region of the jet stream known as the jet left exit.
12:49That's where the strongest part of the jet stream, if you look to the left and where the winds start
12:58to die down again.
13:00If you look to the left of that streak.
13:02So, let's say you've got the strongest part of the jet stream here.
13:05The winds are easing here.
13:08And it's when you're facing the way that the winds are going, just to the left.
13:13The winds are going that way, just to the left.
13:16That's called the left exit.
13:18And if you want to find out more about why the left exit of the jet stream causes rising air
13:24at the surface, then we'll post the link to Alex's deep dive in the description.
13:29But that's what we're seeing here through South Asia.
13:34Jet stream shifted south, encouraging a lot of rising air across Bangladesh, northeast India and so on.
13:43And that is the main reason that we've already seen some extreme rainfall in this region.
13:51And it's going to happen again.
13:53It didn't just happen earlier this week.
13:55Another pulse in the jet stream comes along through Thursday into Friday.
13:59This is a snapshot for midday Thursday, UK time.
14:03And it's again showing this south shifted jet through the Bay of Bengal.
14:09And in this region, then a lot of rising air as a result.
14:13So that's the primary reason that the rainfall is so extreme this week across eastern parts of South Asia.
14:24And the worrying thing is that, yeah, these events have happened in the past, but they've happened with a greater
14:36number of drier days in between.
14:38But what we're seeing this week is two or three pulses of the jet stream coming along on this south
14:45shifted track right next to each other.
14:47So a whole week of intense rain with very little interruption.
14:51And just to demonstrate that here, we've got the rain that happened in Bangladesh in May 2022.
15:02And so the dates are here. This is the first of May.
15:05And this is this is these are all the observational values from a weather station.
15:10So we've got temperature, we've got humidity and so on.
15:14And then we've got the rain total.
15:18So first of May, 0.1 millimeters, no concerns there.
15:21But if you look further down, we've got 46 millimeters on the 10th of May, 163 millimeters on the 14th
15:31of May.
15:32104 again on the 19th of May. But there's a five day period in between with not much rain.
15:37So we've got an incident there where in May 2022, we did have a lot of rain.
15:43163 in one day, for example, followed by a few days later, another bout of very intense rain.
15:49And millions of people were affected by river flooding, flash flooding and so on.
15:54So we know that this amount of rainfall caused serious impacts back in May 2022.
15:59The concern this week is that we're going to see spells of very intense rainfall like this,
16:05but with fewer days in between or no days in between rather of drier weather.
16:11This is the same thing, same location, Srimangal in Bangladesh, showing the last few days.
16:1928th of April on top. So this is this week so far.
16:23167 millimeters on the 28th of April.
16:2827th of April, 70 millimeters of rainfall.
16:3430 millimeters of rainfall on the 26th of April.
16:37So the rain is already adding up.
16:40We've already had some very wet weather in this region and similar values are expected during the next week or
16:47so day by day.
16:51Another way, because this is the deep dive and we like to go super in depth about these things.
16:57And as a result, hopefully we all learn some more meteorology.
17:01Another way of looking at this is through a tephigram, through a profile of the atmosphere from the ground up
17:09to the top of the atmosphere,
17:11known as the tropopause. And I've got one of those profiles here.
17:17And just to set the scene, here's a map zoomed in.
17:22Bangladesh here. We've got northeast India up here.
17:27Dakar in Bangladesh, just there.
17:31Bear Bengal here.
17:32And this cross here is the location I'm going to describe in terms of the atmospheric profile.
17:39Well, just before I move on to that, the colors indicates what is known as Cape or convectively available potential
17:48energy.
17:49So that's an indication of how much energy there is in the atmosphere for updrafts, for air to rise and
17:55release moisture and lightning and hail and downdrafts and strong winds and all of that sort of thing.
18:04So this is an indication of how much energy there is in the atmosphere.
18:07And we're looking at values of 4000 joules per kilogram on a widespread scale in this region, which is considered
18:15pretty extreme.
18:17So I've got a model atmospheric profile from the surface up to the tropopause for this area.
18:28And it's just an interesting way of demonstrating all those different aspects of the atmospheric dynamics that I mentioned at
18:37the start there.
18:38What does this show? Well, imagine you sent up a weather balloon and it recorded air temperature and it recorded
18:47dew point and it recorded wind speed.
18:50We often get readings like this that we put into graphs like this from weather balloons, actual readings.
18:57This isn't an actual reading. This is a computer model projection.
19:02So this is what the computer model reckons it would look like if a weather balloon was sent up from
19:08that part of Bangladesh into the atmosphere.
19:11And the key things to understand about this chart are that, first of all, it's all slightly tilted.
19:17So the blue dashed line here is where you've got zero degrees Celsius and then the black line here is
19:26the air temperature.
19:28So as that imaginary weather balloon rises through the sky, it cools as you typically expect when you go higher
19:38up in the atmosphere.
19:39But it goes rather than a very, very tilted line like that, the whole graph has been transformed.
19:47So it's more upright because that's easier to interpret.
19:51So here's the air temperature. It's this solid black line going up here that a imaginary weather balloon would record
19:58through the atmosphere.
19:59This is what the model reckons it would look like. That's the air temperature.
20:02And it goes through. It starts at 32 degrees Celsius at the surface, cools down to zero degrees Celsius up
20:10here, about 15,000 feet in the atmosphere.
20:12The height is measured in hectopascals because pressure consistently goes down as you go higher up in the atmosphere.
20:19So it's a good way of representing height.
20:22So it goes through zero degrees Celsius there, keeps cooling down.
20:26There's minus 20 degrees, cools all the way down to about minus 60, way up at the top.
20:32So it starts at minus, it starts at plus 32, cools all the way down to minus 60.
20:37That is a rapid rate of cooling, by the way, and that's significant when we're talking about these kinds of
20:43diagrams.
20:45Another thing to point out here is that this is the dew point.
20:48So the dotted line here is the dew point as you go higher up in the atmosphere.
20:53It starts off really quite high. So it's 32 degrees Celsius air temperature at the surface, 25 degrees dew points.
21:00That indicates that we've got hot and very humid tropical air right at the surface.
21:05So those southerly winds coming from the Bay of Bengal.
21:09That's what we're starting off with.
21:11Now, the fact that the actual air temperature cools so quickly as you go further up,
21:18that's a key aspect of the forecast because that indicates that the air is really unstable.
21:24Imagine a hot air balloon.
21:26You heat up the hot air balloon and it rises to the atmosphere.
21:30The more heat you put into the hot air balloon, the quicker it rises.
21:34But what if you were to do it the other way around?
21:37Rather than adding more heat to the hot air balloon, you cool the surrounding atmosphere more, if you could.
21:42So the hot air balloon remains warm, but the air around it gets colder.
21:48Again, the hot air balloon would rise more quickly.
21:52So that's the key thing here is that when the actual air temperature of the surrounding air cools really quickly
22:01as you go higher up,
22:02then any air at the surface that's, say, 32 Celsius and full of moisture,
22:08any of that air that starts to rise will keep rising because it's always going to be warmer than the
22:15surrounding air.
22:16And the limit on that rising air in terms of its cooling, well, that's determined by physics,
22:22because if you take a parcel of air and it starts to rise through the atmosphere,
22:29it cools at a rate known as the dry adiabatic lapse rate.
22:34And that's typically about 10 degrees per kilometer.
22:36And what happens then is that as it rises, it cools and it condenses.
22:42So you've got a certain amount of moisture within that parcel of air.
22:47In this case, a lot of moisture.
22:49And the more moisture you've got, the quicker it is before it reaches capacity.
22:54So it cools down, but it's already starting off relatively humid.
22:58So it doesn't take long before it cools enough so that it becomes completely saturated with that amount of moisture
23:07that starts off with.
23:08And once it becomes saturated, it cools less quickly.
23:12It cools then at what we call the saturated adiabatic lapse rate.
23:16And that specific rate varies depending on the temperature, but it's a slower rate compared with the dry adiabatic lapse
23:25rate.
23:26Now, that's what these lines show here.
23:29This line going for 32 Celsius up to the top of the triangle at the surface.
23:34I don't know if you could see that clearly, but there's basically a point at which it becomes saturated.
23:39We know that is the bottom of the cloud because it's become saturated.
23:44So the water droplets come out of that parcel of air from water vapor into water droplets.
23:49So that's a relatively low point in the atmosphere that you've got the cloud base.
23:54After that, the air keeps rising, but it rises at a slower rate.
23:59And as you can see, it's this curved line here, the saturated adiabatic lapse rate.
24:04And as long as that is to the right of what we call the environment lapse rate, that's the actual
24:10temperature of the air surrounding us, then it will keep rising.
24:13And the more it is to the right, the faster it will rise, the more energy it has.
24:20And that then becomes a measure of what we call convectively available potential energy.
24:26And it's this coloured area here, big fat coloured area that indicates that there's a lot of energy.
24:32Because there's such a big difference between that saturated adiabatic lapse rate and the environment lapse rate.
24:38And that is crucial. So it's this amount of energy that causes these really energetic updrafts in these storms.
24:50This is basically representing a massive thunderstorm cloud.
24:55You've got 32 degrees Celsius at the bottom with a parcel of air coming from the Bay of Bengal containing
25:03a load of humidity.
25:05It rises. Doesn't take long before it becomes saturated.
25:08So we've got a low cloud base. From that point, it keeps rising.
25:12It's saturated. So it's full of moisture, keeps rising.
25:15And it rises quickly because it's always, all the way up to here, warmer than the surrounding air.
25:22And that's because the surrounding air is cooling down so quickly as you go higher in the atmosphere.
25:28So we know that the atmosphere is loaded with energy, full of moisture.
25:32And by the way, the temperature and the dew point aren't far apart there.
25:36So all the way up from the surface up to the top, we've got a moist atmosphere.
25:41And that helps to release a lot of precipitation because there are no points in the atmosphere where the rain
25:47dries out or falls through a drier part of the atmosphere.
25:50So we've got all this rain producing part of the thunderstorm cloud and not drying out.
25:56And that is just a perfect example of why the atmosphere is so unstable, loaded with moisture and able to
26:03produce such devastating amounts of rainfall over the next few days.
26:08Because this is going to keep happening.
26:11Large hail, frequent lightning and strong gusty winds.
26:14Speaking of winds, here is the wind imagined from the model atmosphere.
26:20And it's showing southerly winds at the surface and then changing direction so that the subtropical jet stream is more
26:30of a westerly.
26:32And this is known as wind shear, where the wind changes direction and or speed with height.
26:39And it's really important when talking about thunderstorm clouds, because if the wind didn't change much with height, then you'd
26:46have downdrafts effectively in the same location as updrafts.
26:51And so the updrafts happen, but quite quickly, the downdrafts come in on top of them and the storms don't
26:57last very long.
26:58But if you've got wind shear, changing wind direction or changing wind speed, the downdrafts become detached from the updrafts,
27:06allowing these storms to become more organised and allowing them to last for much longer.
27:11Several hours, perhaps dumping an awful lot of rainfall each time.
27:16So hopefully all of that has given you a good insight into the dynamics of the atmosphere in this really
27:24quite extreme weather event that we're going to witness over the next few days.
27:29One last thing to mention, top of that thunderstorm cloud, minus 60 Celsius.
27:33Imagine that you're starting off with 32 degrees at the bottom, all the way up minus 60 Celsius.
27:39And it's in fact these tropical thunderstorms where you can have the lowest temperatures in the troposphere,
27:46because you've got such an amount of rising air that it just pushes it way, way, way, way up higher
27:53compared with the kinds of clouds that we get at our latitudes.
27:57So really quite extraordinary. Now, back to the UK's weather and thankfully nothing as severe as that.
28:06A few things to mention. One, it's going to be a lot of sunshine over the next few days.
28:12Two, it's unlikely to last into the bank holiday weekend.
28:17But just to emphasise, because I don't like using the word unsettled for the kind of weather we're looking at
28:23for this weekend.
28:24Just to emphasise, there'll still be some dry and bright weather around Saturday, Sunday and Monday.
28:30So don't lose all hope. We're not calling it a washout this weekend.
28:34It's just turning more mixed. There'll be more cloud. There'll be more rain and showers around.
28:39Yes, but it's not going to rain everywhere all the time.
28:41Some places will have reasonable and lengthy dry interludes, but it's becoming messy.
28:48At the moment, it's not that messy.
28:50Now, we have seen some cloud and some showery rain over the last few days.
28:54Here's the bigger picture across the UK. High pressure has been sitting just to the northeast of the country for
29:00some time.
29:01That's allowing a lot of sunshine and that sunshine now returning after a brief interruption on Monday and to the
29:09start of Tuesday, courtesy of this.
29:12You can see it where you're looking. It's an upper trough.
29:17So the main part of the jet stream comes up over Iceland and to the north of the UK, allowing
29:22this large surface high.
29:25But we've also got this weaker filament of the jet stream just pushing in from the east.
29:31And that's increased the cloud and some showers over the last 24 hours.
29:35And this occluded feature now is clearing the south and southwest.
29:39A clearer way of showing that, perhaps, is to put this back on.
29:45And this is, again, the temperature at 300 hectopascals and the wind at that level in a bit more detail.
29:52And you can see this swirl at the moment at the time recording this area of low pressure in the
29:56upper atmosphere running along the English Channel.
29:59If I skip forward to Wednesday, you can see what happens.
30:02High pressure rebuilds both in the upper atmosphere and at the surface across the north and northeast of the UK.
30:09But this upper low, this swirl, runs along the channel and then becomes stationed just to the southwest of the
30:16country.
30:16You can see some weather fronts attached to it.
30:19So there's an exception to the generally sunny and dry story that we're talking about for the rest of the
30:26UK.
30:27And that exception is across the southwest over the next few days.
30:31This is Thursday, 9 o'clock.
30:33Big area of high pressure both in the upper atmosphere and at the surface there across many parts of the
30:38UK.
30:39With that high moving a little bit further east, we're going to draw up warmer air from the south.
30:43So that's one of the things that we'll all notice.
30:46It will become warmer through Thursday into Friday.
30:49But this low pressure, this swirl, remains close to the southwest.
30:54Meanwhile, staying on this graphic for just a bit longer, we've also got this upper trough, this upper low coming
31:03along, moving into Iceland at this stage.
31:06The shape of this and the strength of it is going to be determined by some very lively convection, some
31:14very lively thunderstorms that are taking place across the US today.
31:18And the extent to which they affect this part of the jet stream during the coming days is a little
31:24bit uncertain.
31:25And that will then determine the location and the timing of some rain going into the weekend.
31:30But effectively, what we've got over the next couple of days, this upper trough coming along, this upper low here.
31:36And then they kind of join forces, as you can see.
31:39Friday, that extends south, kind of meets up with this low, which isn't moving very far.
31:45We're still at weather fronts affecting the southwest of England.
31:48And into Saturday, again, it's kind of all becoming a bit messy.
31:52We're still at this upper low here to the southwest.
31:56It's starting to influence things across southern parts of the UK a bit more.
32:01These darker colours, by the way, that's where the air is much colder at the level of the jet stream.
32:07And that will more or less move into the south heading into the weekend and a similar thing happening across
32:14the north.
32:15So we're being attacked by both sides. Low pressure coming in from both sides with associated rain or showers occurring
32:25at the same time.
32:26But as you can see, Sunday, it's all looking very messy.
32:33Let's take that off, put the other visualisation of the jet stream on.
32:37The jet stream's not that strong. That's why I put the other layer on, because it's easier to see some
32:42of the finer details.
32:44So weak, which is typical at this time of year, but it's enough to introduce some instability into the atmosphere.
32:51Similar to South Asia creates that vacuum effect right at the top of the troposphere and causes air to rise.
32:59So we're going from a situation where we've got high pressure, descending air into the weekend.
33:05More likely rising air across parts of the UK, not everywhere at the same time.
33:11Most likely from the south it starts and from the north, and then it all gets very mixed through Sunday
33:17and Monday.
33:18So with no deep lows coming along with with no powerful jet streams involved.
33:23Well, you wouldn't call it unsettled. It's not wet and windy, but it is turning more showery.
33:30There'll be rain and showers around. There'll be drier and brighter weather around as well.
33:33There'll be a lot more cloud. And right now to say exactly where it's going to rain and when because
33:42of that really messy state of the upper atmosphere and the surface level of the atmosphere is a bit tricky.
33:50And we're really not going to be able to get into the finer details of that until a couple of
33:56days before.
33:57So what can we say for now? Well, Tuesday turning increasingly sunny from the east.
34:03This is Wednesday, one o'clock. As you can see, barely a cloud on the map across the UK.
34:08But we do have some cloud and some showers in the far southwest of Cornwall, Isles of Scilly.
34:14High pressure sitting in the North Sea and breezy for the south and southwest in particular, but turning warmer.
34:21Thursday, we've got that. Here it is.
34:26That upper trough coming along into Iceland, starting to influence the low pressure in the upper atmosphere towards the southwest.
34:33And you can see the result. This blossoming area of rain more likely to affect the Republic of Ireland.
34:39But later on, starts to gradually come further east.
34:45Very gradually, northwest Scotland as well affected.
34:48By Friday, a lot of that fizzles out, but we've still a bit more cloud across the north and the
34:53west.
34:54Plenty of sunshine elsewhere. Warmest day of the week.
34:57Mid-20s possible. Anywhere from the southeast of England up towards north Yorkshire.
35:03By Saturday, increasingly, we've got weather fronts coming in from the north.
35:09Weather fronts coming in from the south. Increasing cloud.
35:12Spells of rain and showers, but these are slow moving.
35:15There could be some intense downpours there across the east and southeast.
35:20Even some rumbles of thunder.
35:22Because not only have we got the rising air because of the those small filaments of the jet stream in
35:29the upper atmosphere.
35:30We've also got a bit more of a low level, humid flow in the surface winds coming up from northern
35:37France.
35:38So, a couple of things going on there. But, yeah.
35:41Saturday, there's some heavy rain around.
35:43Into Sunday, it looks like it turns a little bit more showery, but always the potential for other spells of
35:49rain to turn up.
35:50And you can see how messy it is across the UK.
35:52Some places keeping the dry and bright weather.
35:55Other places experiencing some outbreaks of rain.
36:00And the winds all over the place often light, not particularly steering anything into any coherent direction.
36:07So, suffice to say, this bank holiday weekend is looking like a marked change compared with the widespread sunny skies,
36:14except for parts of Cornwall, of the next few days.
36:18But, a lot of uncertainty about the detail.
36:20And it's one of those where it's, if you've got outdoor plans, it's not a washout by any means.
36:25It's not widely unsettled.
36:27But it will be best to stay across the most recent forecasts.
36:32Check the rainfall radar and the forecast rain on the Met Office app and all of that sort of thing.
36:37Just to make sure that you make the best of any dry weather that will be around through Saturday, Sunday
36:43and Monday.
36:44Thank you for watching this week's Met Office Deep Dive.
36:47Let me know if you've got any comments or questions.
36:50We try our best to answer as many of them as we can.
36:53And often we answer your questions in the upcoming Friday's Weather Studio Live,
36:57which is this Friday at Court Pass 12.
37:00If you subscribe to our YouTube channel, of course, you'll be able to stay up today with all of these
37:04latest forecasts.
37:05But, for now, thanks for watching and bye-bye.
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