- 3 days ago
This is an in-depth Met Office UK Weather forecast for the next week and beyond. Sudden warming in the stratosphere but does it mean anything for our weather in December? Bringing you this deep dive is Met Office meteorologist Alex Deakin.
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NewsTranscript
00:00The stratosphere is suddenly warming up, but I wouldn't get too excited about it if you're after snowfall.
00:07We are going to see the UK getting a little warmer this week before potentially some heavy rain across the south this weekend.
00:16I've got an impressive dangler to show you and somewhere in the world may see a metre of rainfall this week.
00:25It's all in this week's Met Office Deep Dive.
00:28Welcome along. My name is Alex Deakin. I'm a meteorologist here at Met Office HQ.
00:33We do this every Tuesday. We look at one, two, three elements of the weather and try and dig a little bit deeper.
00:40So for the next 20 to 30 minutes, that's what we'll be doing.
00:44But we also love reading your comments. So please put them in the chat.
00:49Any suggestions for other topics that we might like to cover, please do put them in there.
00:54Hit the thumbs up button as well.
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00:59Let other people know that we talk about the weather every Tuesday in great detail here on the Met Office YouTube channel.
01:06Thank you very much for being there. As I said, welcome along.
01:09We will start way up in the sky in the stratosphere where, yeah, some funky things are happening.
01:17Let's take a look, first of all, at the temperature way up in the sky, 30 hectopascals.
01:24So what's that, mid 20,000s of meters, 22, 25 kilometers up in the sky.
01:31So way up above the North Pole.
01:35This is data from the JMA, the Japanese Meteorological Agency.
01:40And it is showing the temperature, the current temperature way up in the sky.
01:45This is the average as we go through the year.
01:49So the temperature above the North Pole tends to dip as we go through autumn and into the winter months
01:54before steadily rising as the as the earth tilts back towards the sun and northern hemisphere.
01:59And we see those temperatures rising through the summer.
02:02This is the average temperature.
02:04This is what is happening this year right now.
02:07And you can see, voom, in the past couple of days, temperatures have really started to rocket,
02:12say, way up in the sky, way up in the stratosphere above the North Pole.
02:16And that is stratospheric warming.
02:19And it's happening suddenly, sudden stratospheric warming.
02:23But that's only one part of the equation.
02:26That's the temperature, yes.
02:28But really, we're more interested in what the winds are doing.
02:32High up in the sky at the same levels or a bit above, this is a 10 hectare Pascal,
02:36so close to 30 kilometers up in the sky.
02:40This graph from the ECMWF is showing us what the winds are doing.
02:47Now, usually at this time of year, as we go into the winter months,
02:50the polar vortex sets up high in the stratosphere.
02:55It's kind of a donut of winds.
02:57They go in a westerly direction.
02:59They set up every year.
03:01This year, though, it has been a little bit weaker than normal.
03:04The polar vortex has been a little bit weaker.
03:06And recently, it's got even weaker still.
03:09This is the average wind speed.
03:11Winds in meters per second.
03:12This red line is the average wind speed.
03:15And the blue is where we're at at the moment.
03:17And these lines going forward in time,
03:20well, they're the projections from the different ensemble members,
03:24from the different computer model runs going forward.
03:26And this is where we're at at the moment.
03:28So close to zero.
03:30Now, for a full-on SSW, the winds need to reverse.
03:34So we've got these westerly winds going round and round.
03:37Normally pretty fast.
03:38Can be 150 miles an hour.
03:41But every now and then, they do tend to weaken.
03:43And that's what they've done.
03:44So they're close to zero at the moment.
03:46If they go negative, that means the winds have gone easterly.
03:48And that's when you've got a full-on SSW.
03:51They haven't got there yet.
03:52And they may not get there.
03:53They're expected to stay pretty weak,
03:55maybe dipping back close to freezing over the next week or so.
03:59But the polar vortex has definitely had a wobble.
04:02It's definitely weakened,
04:03which is why we've seen those temperatures shooting up high in the sky.
04:07What does that mean?
04:08Why is it relevant?
04:09Well, what happens with the polar vortex?
04:11If it stays strong all the way through the winter months
04:14and keeps spiraling around,
04:16then that helps to keep the winds lower down,
04:19going in a westerly direction quite rapidly.
04:21So it kind of keeps the jet stream going.
04:24Not the same levels.
04:26The jet stream is way lower.
04:27But what happens is if you've got a strong polar jet,
04:30polar vortex all the way through the winter months,
04:33that tends to keep the jet stream flowing westerly.
04:35And that keeps our weather more mixed and generally in from the Atlantic.
04:38But when the polar vortex weakens,
04:41what can happen is that can ripple down through the atmosphere,
04:45usually takes a couple of weeks,
04:46and that can then let the jet stream weaken
04:51or perhaps even also change direction,
04:54going from more easterly or just breaking down.
04:57And that can allow more blocking weather patterns,
04:59which can in turn allow us things to turn a bit colder.
05:02So that's why people in the winter,
05:03particularly people who love snow,
05:05get a bit excited when they see things like this,
05:07because it can,
05:08but it doesn't always mean that the UK gets colder spells of weather.
05:13What are we seeing at the moment?
05:15Well, this is very early in the season
05:18for us to be seeing a sudden stratospheric warming.
05:22I think the earliest on record was late November back in 68
05:25or something like that.
05:26Well, we haven't got records going back ages and ages
05:29because this is a relatively new phenomenon of recent decades.
05:32But this would be close to a record-breaking early SSW.
05:39Now, it doesn't look like it's going to be a major one
05:41because the wind's not likely to flip,
05:42but a minor SSW is occurring.
05:46What does that mean for us at the surface?
05:49Well, not a great deal at the moment.
05:52Let's put some other charts up.
05:54Now, this is the wind field.
05:58We're going up through the sky here.
06:01So pressure is dropping here.
06:03So we're going up through the atmosphere here.
06:05Now, this is the wind anomaly.
06:07So the change from the average through the sky.
06:12Now, blue isn't cold.
06:14It is actually more or what is less.
06:16The winds are less than average here.
06:19Anything down to those dark blues being the strongest.
06:21So this is a standard zonal mean, zonal wind anomaly.
06:26So this would be higher than average.
06:28The yellows up to the reds, lower than average winds.
06:31Now, the average wind with that polar vortex going would be strong westerlies.
06:35But this is showing much lower than that.
06:38So we've dropped those winds.
06:39So that's what you'd expect.
06:40That ties in with what was observed with those winds.
06:43And we'd expect that dark blue color to be here.
06:48But what would happen or what can happen is that ripple down effect through the atmosphere
06:55that weakens the winds lower down as well.
06:57There is a sign of that as we go forward in time through here.
07:01But it's not a particularly strong sign.
07:04Now, I'm going to take you back five days to what the computers were looking at then or suggesting.
07:10And it's all shifted a little bit because we were five days earlier.
07:14So this is where we're kind of at now.
07:17And there's a stronger signal.
07:18Five days ago, there was a stronger signal for that reversal, that reduction of the winds
07:22to come down through the atmosphere and potentially be much closer to the surface.
07:28And so that would increase the chances of us getting slacker winds, slacker jet stream,
07:34increasing the chances of blocking and potentially some colder weather.
07:37That was a stronger signal.
07:39Much more blue on the chart there.
07:42Let's go back to where we are now.
07:43The more recent runs.
07:45So what we're seeing is the models cooling off on the idea of blocking weather patterns
07:51and actually keeping more likely to keep things more mobile, winds more average.
07:57So average winds would mean coming in from the west.
07:59So we've seen the models over recent days.
08:02Yes, we've got the SSW, but that doesn't always transpose into us getting colder conditions.
08:10It's about 70% of the time when you see a major SSW, that can lead to a colder spell.
08:16And it's always kind of a couple of weeks lag at least.
08:19And as we've seen, the models are not as keen now as they were four or five days ago.
08:24Now, this is all complex.
08:26It's always very complex.
08:27But there's an extra complication added in because it's been so early in the season that can, you know,
08:33the models haven't got as much evidence to go on as well.
08:36So that can confuse the computer models a little bit as well.
08:39If we go back to this one, this chart here showing the projection of the winds, that's the temperature.
08:45But if we show the projection of the winds going forward, you can see that actually most of them try and reestablish those winds as we go through the rest of December.
08:56But that could be in part because they're not used to the winds dropping off so rapidly because this is such an exceptional start.
09:06So the future progress, always take that with a bit more of a pinch of salt when the starting conditions are so anomalous, are so strange, are so unusual.
09:15So difference.
09:16So, yes, we are seeing a strengthening of that.
09:18But even though some of them, as you'd expect, you get a very noisy signal four or five weeks ahead of time.
09:25But there is that stronger signal that it's going to get closer to average, but it never really gets back up to the average even then.
09:31So it could be that through the winter, the polar vortex does remain on the weaker side.
09:36And it certainly started off fairly weak.
09:38So it's definitely something we'll be keeping a close eye on.
09:41As I said, at the moment, there's no strong signal for any colder weather heading for the UK.
09:47As we'll see in a moment, we're looking at milder conditions developing later this week, and that's likely to set in into next week as well.
09:56Now, this is the showing this before on the deep dive, and we often show it in the 10 day trend, the probabilistic pressure trend.
10:01So we're back to the surface now.
10:03What's the pressure doing at the surface?
10:05Dates going forward along the top.
10:07Blue is low pressure dominating close by to the UK.
10:11Red is high pressure dominating close by to the UK.
10:13And we're going back in time again here through previous model runs.
10:17So if we go back, say, to the back end of last week, when there were signs of this SSW happening and people were getting a bit excited,
10:26that could potentially lead to something a bit colder into December.
10:29And look at here. So two weeks ahead of time, just about.
10:34I mean, it's a bit shorter than that, maybe, but quite a bit of red appearing on the chart here.
10:38At that time frame, back end of last week, there was quite a strong signal that through that first weekend in December,
10:45blocking weather patterns may exist, which increased the chances of something a little bit colder.
10:50It doesn't guarantee it could be blocked with high pressure generating southerly winds, but increased chance, certainly.
10:58But as we've gone closer to the more recent days, as I say, the models are backtracking from that thinking a little bit.
11:04Much more blue on the chart as we head into that second week of December.
11:10So much more likely now that we're going to see low pressure continuing to dominate, which means milder and wetter weather as well.
11:17And we take a look at even the wider picture now looking even further ahead.
11:21There's that block of blocks, if you like, from the first weekend of December, from the end of last week.
11:29Even through the weekends, there was signals of perhaps some higher pressure and blocking with those pinker colors there on the middle part of December.
11:36Again, that would be two weeks ahead.
11:39So, yeah, potentially that link to the SSW weakening.
11:43But even that signals now kind of washed away.
11:46What about those reds up there?
11:47Well, that is a long way ahead.
11:49So, yeah, the main signal to pick up on is actually certainly for the first two weeks of December.
11:54It's looking mobile, looking most likely that we will see low pressure close by or in control of our weather, which means milder and wetter weather generally.
12:04With that caveat that the models may not necessarily be handling the SSW that well because it is so early in the season.
12:13So, an intriguing one this winter or starts to this winter, certainly something we'll be keeping a close eye on.
12:19But at the moment, I wouldn't be banking on getting your sledge out anytime soon.
12:25But, you know, watch this space, subscribe, and then we'll be keeping you updated on the very latest.
12:31But quite interesting what's going on high in the sky.
12:35We often get a lot of questions about the SSW.
12:37So, that's where we're at at the moment.
12:40What about in the shorter term?
12:44Because that could be quite interesting as well with our weather, particularly as we head into the weekend.
12:49What we've got at the moment, as you probably could tell, is quite a lot of sunshine outside.
12:56And a few showers draped into eastern areas.
12:59We've got a northerly airflow.
13:01So, the wind's coming down from the north, both at the surface.
13:03And the jet stream is kind of rippling and toppling in over the UK as well.
13:09So, we've got northerly winds high in the sky where the jet stream is and northerly winds at the surface also.
13:17So, let's look at the bigger picture because that jet stream coming down here is creating a dip, making low pressure and lots of wet weather over Italy.
13:25What's going to happen over the next few days is that these weather systems start to move in.
13:31The jet stream topples over the UK and this ridge of high pressure moves in.
13:36Going to be a cold one tonight with those clear skies.
13:39But then we're seeing weather systems coming in from the Atlantic.
13:43The first one bringing wet weather into the west during tomorrow.
13:47And then this one getting picked up by the jet stream.
13:51Notice here, quite an active jet stream, picking that low up, pushing it up towards Iceland.
13:56And if we fast forward that a little bit, it actually turns into quite a powerful little low.
14:00And that squeezes the ice bars and brings some pretty strong winds to northwest Scotland.
14:05As we go through Thursday and more particularly Thursday evening and into Friday.
14:10So, that's kind of the next major watch point with our weather.
14:13What are those winds doing there?
14:15The winds high in the sky.
14:17But the surface winds too are going to be pretty lively close to that low as it zips between the UK and Iceland.
14:22But some strong winds across the northwest of the UK.
14:25Before all that though, tucked in here, this is a warm sector.
14:30So, we've got some warm air on the way.
14:32Let's take those winds off and put the temperature on.
14:37The temperature profile about 1,500 meters up.
14:41That is showing a nice little warm sector in there, tucked in there.
14:45So, some warmer air is on the way.
14:48Let's take a look at what the temperatures are going to do.
14:50Because we're going to see quite a contrast later this week.
14:52In particular, between 6 o'clock tomorrow morning, 6 o'clock Wednesday morning.
14:59Where we could easily see those temperatures down to freezing.
15:02Much more widespread frost coming in tonight.
15:04Whereas, if we fast forward to 24 hours later, just about, temperatures in double figures.
15:15So, we're going to see a big jump.
15:16And this is the temperature contrast from 24 hours earlier.
15:19Many places are going to be 9 degrees warmer.
15:22If not more, if not more, or not more, 9 degrees at least, warmer than 24 hours earlier.
15:30So, yes, a frost tomorrow morning.
15:33And then Thursday morning, far from frosty.
15:36But, of course, as we see that switch and the Atlantic winds coming in, we will see a return to wetter weather also.
15:42But that's going to be quite an interesting switch that we see between Wednesday morning and Thursday morning.
15:47Then, well, things could get interesting into the weekend.
15:52Let's take the jet stream off for now.
15:56And fast forward and zoom in a little bit.
15:59We've got these weather fronts coming through.
16:00So, bands of showery rain coming in.
16:02Look at those isobars closely packed through Friday.
16:04Still very windy across northern Scotland.
16:06So, Thursday night, Friday across northern Scotland.
16:09Very windy.
16:10The isobars more spaced out elsewhere.
16:12Then, just watch this.
16:13A little dip in the isobars.
16:18Now, that actually develops into quite a nasty-looking little low-pressure system heading in towards the southwest of the UK on Saturday.
16:27Now, it does look as if this is the Met Office computer model is maybe over-egging this, intensifying this low a little bit too much.
16:35But this low certainly has the potential to bring more heavy rain across the south and also possibly some strong winds.
16:42But it does depend on the intensity.
16:44I am going to put the jet stream back on now because how that develops really does depend on how the jet stream picks it up.
16:52So, the jet stream coming in here, and it gets quite complicated, kind of splits into two around this zone.
17:00And it's this little left exit part of this jet streak that picks that up and intensifies it and pushes it as quite a deep area of low pressure into the southwest of the UK.
17:11Now, we don't think it's going to be this intense because of the complexities of the jet stream as it picks it up.
17:18Other models are not suggesting it's going to be as intense.
17:21In fact, there's quite a big spread, quite a big variation in what the other computer models are doing with this area of low pressure,
17:29which I can hopefully show you if we look at the ECMWF ensembles.
17:37So, this is the European model.
17:39Let's get to the same time frame.
17:41Gone too far.
17:42Saturday.
17:44Saturday midday.
17:46This is what ECMWF, the European model, has.
17:50It's got a low and it's not due to dissimilar position on its control run.
17:56So, heading in more into northern France and not as intense as the Met Office model.
18:02But if we look at the other members, so we run the model many times.
18:07That's number one is down here.
18:09It's got a, well, maybe a slightly more potent low, but it's in a much more southerly position.
18:15Where has it gone on number two?
18:16Well, there's something weak in the Bay of Biscay.
18:18Not much happening across the south of the UK at all.
18:20So, that would be very different.
18:22Looking at number three, it's got a low heading somewhere across Wales and into northern England.
18:27Number four, I think, is even further north.
18:29So, just taking the first handful of ensembles, you can see quite a spread.
18:33Now, there is a consistency.
18:34There's a low pressure kind of in this zone.
18:36But how far north it is, how far south it is, that is quite a range.
18:41Now, just looking at individual runs of these ensembles, isn't that useful?
18:44So, we tend to look at probabilities or we look at the position of the lows and compare them to each other.
18:51This is, let me show you this first, actually.
18:54This is the Dalmatian plot.
18:57So, each of these different dots represents where the center of the low is on each of the different ensemble member runs when you run it many times.
19:07The top two are from ECMWF, from midnight last night and from midday yesterday.
19:13And the Met Office ones for the same time frame are on the bottom two here.
19:18Now, let's zoom into what we were looking at yesterday.
19:22Quite hard to see.
19:23I appreciate that.
19:24But there's the outline of the UK and the European model.
19:27Got more of a cluster down across France.
19:29So, the European model was favoring those low pressure systems to be down across northern France, which could still bring some heavy rain across southern England.
19:38But it does have some across parts of England and Wales.
19:41Whereas the Met Office model, the main run, actually had the low exiting Yorkshire.
19:48But it does have that cluster down.
19:50But it's much more spaced out.
19:51So, much less consistency there with the Met Office model.
19:55But if we go to the more recent run, look at the run from midnight last night, you can see the Met Office run here has that really deep low that we saw down to the southwest.
20:07A lot of other ones close by to it in here.
20:10But those purple colors, that means the low isn't as intense.
20:14So, that's why we think our model, that main model run, the deterministic model run, is too deep, is too intense with the low.
20:22Because a lot of the ensemble runs are nowhere near as intense, but in a similar position.
20:27So, we're reasonably happy with that position.
20:30European model run now, again, has that cluster.
20:33Still further south than the Met Office model.
20:36But it's a little close.
20:37It's more likely across the channel.
20:39So, the models are kind of converging.
20:41If we get close to the time, they're getting more consistent as well.
20:44So, we do think we're going to see low pressure.
20:47The most likely scenario is a low pressure somewhere either across the south of England or across the channel or northern parts of France.
20:55There is still a small chance, but it is a small chance, about 10%, that it is like the Met Office model and quite an intense low.
21:01But the most likely scenario is that it is a low pressure system, that the winds don't cause too many issues.
21:07But, of course, because it's been so wet, any amount of rainfall needs to be watched at the moment.
21:11So, that's the most likely scenario.
21:13If you look at the probabilities, again, this is just from the European model run.
21:17When you run it lots of time, you can work out the probability.
21:19If you look at number one has a certain amount of rain, number two doesn't.
21:23So, you can work out the probability across those 100 members.
21:28And this is showing the probability of 10 millimeters of rain.
21:31So, how many of those 100 ensemble members are showing 10 millimeters of rain?
21:36So, it's not actually showing where it's raining.
21:38It's the probability, the chance of 40 to 60% chance in that zone here from the European model of what we call probably heavy rain through the English channel.
21:49I can zoom in a little bit, show that a little bit closer.
21:53So, that's the main area we're looking at.
21:55But this is the European model.
21:56We think that's still a little further south because our Met Office model is a little bit further north.
22:00So, the most likely scenario is that it's quite wet through that southern slice of the UK with the possibility also of some strong winds too.
22:08So, that's what we're focusing on in the short to medium term as we go through this week.
22:13Alex Burkill will have much more on this, no doubt, tomorrow when we'll have had a couple more iterations.
22:18The model said they'll probably converge a little bit.
22:20Now, this is five days away still.
22:22So, you know, we will get more firmed up on it as we get closer to the time.
22:27But there is the potential, just showing it at this stage, for some pretty wet weather across parts of the south as we head into the weekend.
22:35And, of course, as I said, it's been pretty wet recently.
22:38So, one to watch.
22:39Alex Burkill will have much more on that in the Met Office 10-day trend tomorrow.
22:48But, yeah, some interesting weather coming our way.
22:50We're talking about 10 millimeters of rain.
22:51I am now going to talk about the potential for a meter of rain in Sri Lanka.
22:59Let's take a look at the rainfall patterns around the world.
23:03What do we want here?
23:05We want that and the rain.
23:06We take the jet stream off.
23:08So, let's head over to Sri Lanka where things are getting very interesting indeed.
23:14So, where are we?
23:15There's Indian subcontinent.
23:17Sri Lanka is under here.
23:18Let's take the rainfall off just to get your bearings there.
23:20Sri Lanka.
23:21This is the pressure chart.
23:22That's not really that useful at the moment because it's quite a weak circulation that we've got.
23:26But we can put the winds on.
23:27That will show it quite nicely.
23:29Well, we've got the winds coming down from the Bay of Biscay.
23:32The northeasterly monsoon winds at this time of year coming down here, meeting the south, southwesterly winds coming in here.
23:41And that is a recipe for winds merging together, as we'll see more of in a second, actually.
23:46The winds merging together, pushing up, generating clouds, generating precipitation, quite a lot of precipitation as well.
23:53Let's just play through the next few days.
23:55Take the pressure off.
23:56We don't really need that.
23:57But you can see those winds coming up, clashing, circulating around.
24:02And just look at that rainfall, keeping going, keeping going, keeping going through Wednesday.
24:07Again, I'll just take that off.
24:09That is Sri Lanka under there just to get your bearings.
24:11Let's zoom in a little bit because that rain, as Colombo's appeared, as if by magic.
24:18Look at that rain, keeping going, feeding in, got very warm, moist sea.
24:23A moist sea, who'd have thought it?
24:25Feeding in all that moisture.
24:27So this part of the world going to see some very, very heavy rain over the course of Wednesday, Thursday, still going into Friday as well.
24:35May well generate into actually a tropical depression.
24:37Not particularly strong in terms of its wind strength, but because it's slow moving and you're just feeding in all that moisture day after day after day, you know, the rest of this week still going into Friday.
24:52That is a lot of rain to fall over this part of the world.
24:56Now, this time of year, you always get the northeasterly monsoons.
24:59You always get some kind of a clash going.
25:01So it is the wettest time of year in Sri Lanka.
25:03Normally, the island gets about 250 to 300 millimetres of rain through November.
25:08That's the average, broadly speaking.
25:11Compare that to, say, London, which is about 500 millimetres.
25:14So about half of London's annual rainfall falls in November in Sri Lanka.
25:21So it's a wet time of year for sure.
25:23But this is above and beyond that.
25:25That is a very soggy spell of rain thanks to this tropical depression.
25:30It's still going, look, even into Friday, it's not even until the weekend when it starts to move slowly further north.
25:35So we are a little bit concerned about the rain in this part of the world, likely to cause some issues.
25:41How much rain are we talking?
25:42Well, this is I want to say a big thank you to Nick Silveston for the for the for giving me this chart.
25:50By the way, he's on deputy chief at the moment.
25:52He was looking at this, giving me all this information.
25:54So a big, big shout to Nick.
25:55Thank you for that.
25:56This is the average rainfall from three main models that we that we tend to look at.
26:01So the Met Office model, ECMWF and GFS, American model averaging over this part of the world.
26:08So this is Sri Lanka.
26:09This is the average rainfall until the end of the week.
26:11And there's a peak there across that northeastern coast, 478 millimetres.
26:15Now, this is averaging over relatively coarse models.
26:21It's going to miss the extremes.
26:23So Nick reckons we could easily see double that.
26:25We could easily see 800 millimetres of rain and possibly some spot totals of a thousand millimetres of rain.
26:31What is a thousand millimetres of rain?
26:32Yes, that's right.
26:33It's a metre, a metre of rain falling through the rest of this week.
26:37And what?
26:39Two, three times the monthly average if we see that kind of amount of rainfall.
26:44Admittedly, it's over the hills, over the high ground where we'll see those totals.
26:48But there's a real risk of flooding.
26:50Nick was also showing me charts of rivers and the returns and how much we'd like to see one in 20 year flooding events on a lot of the rivers across the north of the island.
27:02But even further south, there's a 30, 25 to 30 percent chance of seeing these returns of a one in 20 year river flooding event.
27:12And this is a part of the world that gets a lot of rainfall.
27:14So this is quite unusual.
27:16And as I say, could cause some problems through the rest of this week as those rainfall totals really, really build up.
27:22Again, 478 millimetres.
27:24Again, that's not really picking out the extremes.
27:26So we could see almost double that in some locations.
27:29Just for comparison, London gets about 500 millimetres of rainfall every year.
27:34So, yeah, quite a lot of rain likely to fall in Sri Lanka from that developing situation there.
27:41One more thing I wanted to show you.
27:43I did promise you a dangler at the start.
27:45And yes, I will show you that now.
27:49In fact, I'll show you it right at the start of the satellite sequence.
27:52Going back to last Thursday, if we zoom in.
27:55Then coming down here, we have an example, quite a good example, of the Pembrokeshire dangler, where the winds come down from the north and generate showers through the Irish Sea, which hit Pembrokeshire, often go on to hit Cornwall as well.
28:12Sometimes Devon, the islands are silly.
28:14And we saw it last Thursday.
28:17Last Thursday, it was very cold air and it was generating a lot of snowfall.
28:22So we've seen some fantastic pictures of snow in Pembrokeshire.
28:26People have been skiing 20, 30 centimetres of snow, more in some drifts.
28:32So, yeah, incredible amounts of snow from the Pembrokeshire dangler.
28:37What is the Pembrokeshire dangler?
28:38It's a genuine meteorological phenomenon.
28:40It should really be called a convergence line because that's what happens where the air converges.
28:46Not dissimilar to what's happening in Sri Lanka.
28:50The rainfall totals, though, thankfully, somewhat significantly less.
28:54So that was last Thursday.
28:57But today's, this is today's weather chart and it's back.
29:02That's what it looks like on a weather chart.
29:04So this is the pressure chart from midnight last night.
29:06Got the low pressure, the black lines, the isobars, the purple, the occlusion.
29:12You've got your warm front, your cold fronts.
29:14There's a whole video all explaining about these pressure charts that myself and my colleague Jody made earlier this year, I think it was.
29:22We'll pop the link in the description.
29:24All about how to read a pressure chart.
29:26But, yeah, on it, you can see the Pembrokeshire dangler.
29:30There's a close-up of it.
29:31A convergence line looks a bit like a stick because it means the air is coming together.
29:37The air is clashing and it's being forced up, generating precipitation.
29:41Let's take a closer look at what's going on.
29:46In fact, let's do it on the, let's show you the radar from today.
29:56So you can see it quite clearly here.
29:57So this was yesterday, yesterday afternoon.
30:02We had a circulation, a lot of wet weather and just bands of showers coming through, really.
30:06You can almost see it setting up there with the winds coming around, low pressure like that.
30:10But if we run through the sequence, it's been more in evidence through the day today.
30:16And we've got this classic.
30:17So you've got the winds coming down from the north.
30:19Now they're coming down from the north.
30:20They're being heated from beneath, from the warm sea.
30:22So the warm sea is pushing up warmer air.
30:26It's hitting the colder air.
30:27So it just rises.
30:27And as it rises, it generates clouds.
30:30That's what we're seeing here in the flow coming in.
30:33We saw it last week as well across these eastern areas.
30:36But specifically here, you've got that line going all the way down.
30:40You're not seeing it across Republic of Ireland.
30:42Seeing a little bit maybe there in north Wales.
30:44But it's not as prevalent.
30:47That is because the air is coming right down here.
30:50You've got to get it in just the right location.
30:53So the air is coming right down here.
30:54Not really hitting any land.
30:57Let's put the pen on.
30:58See if we can do some drawing.
30:59Oh, there's my cheats from earlier.
31:03Let's zoom in.
31:06So you can see that the wind's coming down here.
31:10That's the way the wind is coming.
31:12Coming down here.
31:15Generating warmth from beneath.
31:19Pushing the air up.
31:20But what is happening here,
31:22as the air comes down across Northern Ireland into the Republic of Ireland,
31:26what happens is as the air comes over,
31:29as the air is traveling over sea,
31:32the sea is relatively smooth.
31:33As it comes over land,
31:35so use my computer as an example,
31:36there's more friction there.
31:38So it loses energy.
31:40So it slows down a little bit.
31:42So as the air is slowed down,
31:44what happens is the pressure force takes over
31:47and it actually is forced to move back a little bit.
31:52So you get this effect of the wind coming over the land.
31:58And actually it's backed.
32:00It's turned back on a little bit.
32:01So the wind's coming down here are coming like this.
32:03The wind's coming down here just straight over the sea.
32:05They're still coming down from the north.
32:06So what you've got,
32:08where these two are meeting,
32:10you've got a clash.
32:11You've got those winds pushing together.
32:13You've got the winds coming straight down over the sea
32:14and then over Ireland,
32:16they're getting a little bit of a tweak
32:17because they're slowed down the frictional forces.
32:19They're being pushed together.
32:21That is the convergence.
32:23Where can they go?
32:24They can't go down because the sea's there.
32:25They can only go up,
32:26which is generating the clouds
32:28and generating that really nice little streamer
32:31is another word for it as well.
32:32So that's coming down right through there.
32:35And one more thing to show you on that,
32:38high resolution satellite picture from today.
32:42This is from Zoom Earth,
32:44pictures from UMETSAT.
32:45You can see it quite clearly there.
32:46So it starts off with the air coming in,
32:49but you can also see these little feeders,
32:51these little streamers starting to come in.
32:54You can almost see the lines coming together
32:56and that clashing of those start off
32:59as just cumulus clouds bubbling up a little bit
33:02and then they get more and more
33:03and they get more energy
33:03as they get more force together,
33:04they get more pushed up
33:05and they generate the showers.
33:08Now at the moment,
33:08they're of rain
33:09because we've turned a lot milder,
33:11but last week,
33:11that is what generated the snow across Pembrokeshire.
33:14Typical at this time of year,
33:16that's when you get it most
33:17because you've got the cold or the air
33:18coming down from the north is getting very cold
33:21and the sea's still really quite warm.
33:23So you get that contrast between the warmth
33:25at the surface and the colder air loft,
33:27forcing it up along with the physical forcing
33:30of those winds pushing everything together.
33:32So it's a convergence line,
33:34but also known as the Pembrokeshire dangler.
33:37Some people call that the Cornish tickler.
33:40So, you know, take your pick,
33:41but these names genuinely have some meteorology behind them.
33:45Right, that is pretty much it from me for today.
33:48Thank you very much for joining me
33:49for this Met Office Deep Dive.
33:51Hope you enjoyed it.
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34:22That's it from me.
34:23Thank you very much.
34:23Been a lot of fun.
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