This is an in-depth Met Office UK Weather forecast for the next week and beyond. The weather turns rather autumnal this week. What does that mean and how does it differ from the rest of summer so far? And will it last for the Bank Holiday Weekend (for England, Wales and Northern Ireland). Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:00Hello and welcome to the Met Office Deep Dive, our regular in-depth look at all things meteorological
00:06affecting the UK and weather patterns around the world. This is exclusive to the Met Office
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00:20so you never miss one of these updates in the future.
00:23This week, there's plenty to get our teeth stuck into. We've got a bank holiday weekend
00:28coming up for England, Wales and Northern Ireland. We've got a very wet spell of weather
00:33coming up for parts of Scotland. And we've got the remnants of an ex-hurricane to talk
00:39about, as well as something a little more autumnal over the next few days.
00:47Now before people start screaming at me that the summer so far has felt autumnal, I know
00:54because a lot of people were mentioning that in the comments of my week ahead forecast
00:59yesterday, I'm going to argue that there's a subtle difference between the autumnal weather
01:03over the next few days and the relatively cool and changeable summer weather that we've
01:08seen so far during June, July and August.
01:14To put that into context, let's take a look at the averages first of all. The averages
01:18for rainfall and temperature across the UK and across the three summer months up to this
01:24point in August. This graph shows the rainfall amount so far. And up to the 20th of August
01:33or the 19th of August, we've got 185 millimetres of rain averaged over the UK. And that's actually
01:40below this black line, which is what you'd normally expect at this point, or at least
01:46the average up to this point in the summer. And that might come as a surprise to many
01:51of you, and I'll go into further details about the rainfall in just a moment. But yeah, averaged
01:56across the whole of the UK, we are currently running at below average rainfall. As you
02:02can see from that graph, around the mid to late part of July, it was closer to average,
02:07but at the moment, slightly below average rainfall. And very slightly below average
02:13temperatures up to this point in the summer. Not massively below average, just slightly
02:19below average by a fraction of a degree or so. Again, that might come as a surprise to
02:24many of you, and I understand the reasons why. And to understand the reasons why, let's
02:29drill down into the details about the summer weather day to day up to this point. And again,
02:36these are averages across the UK. There are obviously very stark regional differences
02:41from place to place, and I'll explain some of those in a moment as well. And by the way,
02:46if you're not a fan of this kind of in-depth, deep dive into the weather stats, do feel
02:51free to skip ahead to the next chapter, when I'll be going into the forecast for the next
02:55few days and into the Bank Holiday weekend. But for those of you who are interested to
02:59know the kinds of weather patterns that we've experienced so far this summer, and why they've
03:03been cool, changeable, summer-like weather patterns, and not autumnal weather patterns,
03:09let me explain. So, this shows the day to day temperature, the mean temperature, that's
03:14the average of the maximum by day and the minimum by night, each day across the UK through
03:20the last two and a half months or so. And as you can see, there's been a lot of variation
03:25from day to day, but I can identify, I think, several phases of summer weather that we've
03:32seen during the last few months. The first phase, I've identified here, runs from the
03:39first of June to the 19th of June, this period where the temperature was mostly below average.
03:46This was the coolest period of this summer, as you can see, there's temperatures well
03:50below average. And we saw weather patterns that looked somewhat like this. This was the
03:56average sea level pressure for the UK, June the 1st to June the 19th. There's the UK in
04:03the middle, and it shows significantly low pressure there over Scandinavia, high pressure
04:10just to the north of the Azores, and because of this setup, we saw northwesterly or northerly
04:15winds. But with that high pressure ridging into the southwest, we saw the most unsettled
04:20weather towards the north and the east of the UK, drier and generally sunnier weather
04:25towards the south and southwest. It was a sunny period. I know that the last, well since
04:31the end of this period, the last few months have been generally dull and relatively wet.
04:38This period in particular was generally sunny, even if it was accompanied by a cold wind
04:43coming from the north and the northwest. So that's the weather pattern that we saw first
04:48of all, 1st to the 19th of June. I'm going to skip this middle bit for now and move on
04:54to this weather pattern, which was from the 29th of June or so, the 28th of June, up until
05:01the middle of July. And that's the first weather pattern. This is the next one. They both look
05:08remarkably similar if I stand out the way. What you can see is again low pressure over
05:14Scandinavia, higher pressure over the Azores, generally a northwesterly wind direction.
05:22And this was not quite as cool as the first period, but it was wetter. I'd say this was
05:28the wettest period of summer weather that we saw, June the 28th to July the 15th. And
05:34we saw the jet stream to the south of the UK. And we saw a lot of low pressure and a
05:40lot of rainfall. What these two weather patterns have in common, up to the 19th of June and
05:46then 28th of June to the 15th of July, is a south shifted but weak jet stream. Now that
05:52I would say is a typical summer pattern, albeit with the jet stream to the south of the UK,
05:59a relatively cool and unsettled summer pattern. Not an autumnal weather pattern, which I'll
06:04explain what I mean by that in a moment, but a cool, disappointing summer weather pattern
06:09because of the weakness of the jet stream that kind of got stuck in a rut, basically
06:15sitting to the south of the UK. Now ignore that middle bit because this was a bit of
06:20an anomaly. This was the most prolonged, albeit only a week or so, settled period of the summer
06:26from the 20th of June to the 27th of June. Shown in the middle there, the Azores high
06:33stretched across much of the UK, particularly the south. And for many places it was dry,
06:38it was sunnier and it was much warmer. So that was a brief interruption in the other two,
06:46outside of it, where we saw the jet stream stuck to the south of the UK. This one, the jet stream
06:51was nudged north, higher pressure, just for a week before we returned to that south shifted
06:56jet stream. So that sums up the first half of the summer, basically up to July the 15th. Mostly the
07:01jet stream was weak, it was to the south of the UK, it was cooler than average, we saw plenty
07:05of rain. At first it was sunny and then it got increasingly cloudy, but in between there was a
07:10week of fine weather, which is easy to forget because the rest of it was so disappointing if
07:17you don't like cool and rainy weather in the summer. Then the second half of summer looks a
07:24bit different to the first half of summer. Since the 16th of July we've seen much more changeable
07:32ups and downs. So no particularly prolonged cool, wet, rainy spells, no particularly prolonged
07:38hot spells, but more frequent hot spells. A number of them there just spiking above the average line
07:44and then a number of cooler spells just spiking below the blue line. And generally that second
07:50half of summer, from the 16th of July up to yesterday, has been marked by this kind of
07:56weather pattern, which is quite different to that south shifted weak jet stream that we saw during
08:00the first half of summer. And this is how it's looked. Much lower pressure over Iceland, much
08:05higher pressure over the Azores, and a west to southwesterly airflow. A stronger jet stream
08:13coming in from the Atlantic and driving areas of low pressure into the north and northwest of
08:18Scotland, Iceland and so on. So much more unsettled towards the northwest, much more settled towards
08:23the south and southeast. And with more warm spells occurring depending on the shape of that
08:31pattern. Because within that period we did see the hottest day of the year so far and that was on the
08:3812th of August, last Monday. And that, this is the average pressure pattern for the 11th to 12th of
08:46August. It looks quite similar to the whole period but this sub-phase, I would say, for this two-per-day
08:54period, just saw a slight tilting of the pattern to allow higher pressure to bulge in from the
09:00continent and allow this plume of heat to arrive across southern and eastern parts of the UK.
09:06Although towards the northwest we kept more cool and changeable weather. So very similar. We've had
09:12this westerly dominated regime since the middle of summer. A contrast to the south shifted jet
09:19stream during the first half of summer. But within that more general weather pattern, occasionally
09:25it's just tilted to allow some warmer hot spells in at times. Which has given us more of these peaks
09:32in temperature during the second half of summer. And fewer long-lived cool spells that we saw
09:38during the first half of summer. So that kind of puts it into context. I would say that
09:44the first half of summer with a weak and south shifted jet stream, normally during the first
09:49half of summer you get a weaker jet stream compared with the second half of summer because of a reduced
09:55temperature contrast across the North Atlantic. And that is indeed what we saw. But of course
10:01that weak jet stream, some years it sits to the north of the UK, some years it sits to the south.
10:05This year it has predominantly been sitting to the south. Hence the cool and unsettled weather.
10:11Now the second half of summer has seen again a pattern more like you typically get during the
10:17second half of summer. A more strong jet stream developing, more areas of low pressure moving in
10:24from the Atlantic. But at the same time, depending on the orientation of those lows, we have seen some
10:30heat arrive from the continent. Now that second half of summer weather pattern is really nicely
10:39captured in these maps that show the flavour of August so far. The one on the left shows the
10:47rainfall anomaly up to the 18th of August. And it shows a really marked contrast between
10:55Western Scotland, Northern Ireland, Cumbria and the rest of the UK. So this northwest to southeast
11:01contrast where it's been much drier than normal up to this point in August for eastern parts of
11:07England and the south. But we've had about average rainfall for Western Scotland and Cumbria as well
11:14as parts of Northern Ireland. Normally up to this point you'd expect 58% of the average rainfall,
11:19not 100% which is what parts of Western Scotland have seen. So it's been much wetter than normal,
11:24Western Scotland much drier than normal towards the southeast because so many of our weather
11:29systems have been coming in from the west and hitting northwestern parts of the country with
11:33low pressure primarily moving through Iceland. Similarly, average temperatures up to this point
11:39for northwestern parts, above average for southeastern parts. This is for August. June and
11:45July were both slightly below average and that explains why summer up to this point so far has
11:50been slightly below average for the UK as a whole. So over the next few days when I talk about it
11:57becoming more autumnal, I'm not talking about a return to the south shifted but weak jet stream
12:03that we saw throughout much of the first half of summer. I'm talking about an enhanced version of
12:08what we've seen during the second half of summer. This westerly airflow, a stronger jet stream,
12:15deeper areas of low pressure. Those are all the kinds of weather patterns I normally call
12:20autumnal and the reason is because as you get into the second half of summer and more especially
12:26into autumn, you get a stronger temperature contrast across the northern hemisphere, in
12:32particular the North Atlantic. You get colder air starting to return to the North Pole into Greenland
12:36as well as the days start to draw in. You also get tropical systems across the Atlantic moving
12:44north and bringing their tropical humidity northwards and in between this clash leads to
12:51a strengthened jet stream and that is what we're going to see over the next few days. We're going
12:56to see all of those things, colder air moving in from Greenland, tropical systems moving north and
13:01bringing enhanced warmth and humidity and along that boundary, that temperature contrast, we're
13:07going to see a strengthening of the jet stream and more areas of low pressure over the next few days.
13:12That means more wind and more rain, certainly a windier spell over the next few days compared with
13:17what we've often seen through the summer so far and a very wet spell for northwestern parts of the UK
13:24Wednesday into Thursday and as well as that into Friday. So let me just show you how that plays
13:31out. First of all we've got the jet stream sitting to the south, just to the south of the UK at the
13:36moment but it's running in a relatively straight line across the UK, a showery day on Tuesday
13:42and then playing that through the next few days you can see plenty of lows there over the Atlantic
13:48moving in with various weather fronts. This low moving up towards Iceland initially on Wednesday
13:55but then this low coming along and sitting to the south of the UK, that's going to be the feature
14:03responsible for the very wet spell that I'm talking about for later Wednesday and into Thursday.
14:07Where does this low come from? Well this is in fact ex-hurricane Ernesto. So rewinding to the
14:15beginning to show you where that comes from. At the time of recording it's just moving off Newfoundland
14:21there. That is ex-hurricane Ernesto brought some significant impacts to the Bahamas, to Puerto Rico
14:28last week and it's now moving into the cooler air waters of the North Atlantic. It's not unusual
14:35at all for hurricanes at this time of year of course August, September, peak hurricane season, they do
14:42tend to very often move north into the cooler waters of the North Atlantic. When they leave
14:49behind temperatures of 27.5 degrees they do of course become removed from their fuel source
14:57and so they start to weaken rapidly and that's what's happening as you can see to Ernesto. These
15:03isobars are going to open out but at the same time they can be picked up by the jet stream
15:10and become extra-tropical cyclones. That's what they're called rather than tropical cyclones, they
15:15become extra-tropical cyclones out of the tropics and they transform into more typical mid-latitude
15:21lows. On the face of it they're just like any other lows that we get moving in along the jet stream
15:28and arriving at the UK. So they're not hurricanes when they hit the UK of course, they've lost
15:33a very warm water fuel source and they're instead powered by the jet stream which is what all our
15:39low pressure systems tend to be powered by. However there are a couple of important things in terms of
15:47their tropical origin. One is that they can lead to a lot of uncertainty in forecasts because
15:55their origin means that they start life as very small but very powerful features and because
16:01they're small they're not as easy to model compared with large areas of low pressure. So
16:06that's one reason they are often a little bit more uncertain compared with more typical areas
16:13of low pressure that turn up in the mid-latitudes. Another important thing to note about these
16:20extra-tropical systems that have tropical origins is that they tend to contain a lot of moisture
16:25and that's why this one in particular is notable. So we're fortunate in that Ernesto doesn't look
16:33like it's going to cross onto the cold side of the jet stream. If it crossed onto the cold side it
16:37would deepen more vigorously. As it is it's generally just going to meander into the warm
16:43side of the jet stream allowing it to be transferred across the Atlantic and it will generally lose its
16:51identity and merge in with this cold front that dangles from a more typical mid-latitude load
16:57that's moving into Iceland. But here's the important thing, when it arrives during the
17:05second half of Wednesday and into Thursday it's pumping a lot of warmth, put the temperature on,
17:12a lot of warmth, you can see it there, the swathe of warmth and moisture that comes from the tropics
17:19and that leads to an enhancement of the rainfall across western and most notably
17:25northwestern parts of the UK. So just to give you an overview of what we can expect through
17:31the day on Wednesday, rewind slightly, it starts off dry Wednesday but during the morning you can
17:40see this swathe of persistent rain setting in across Scotland, Northern Ireland, Cumbria,
17:46eventually North Wales as well. The bright colours then starting to show up through the
17:51afternoon across western Scotland, that means the rain's turning heavier. It's going to be
17:59enhanced orographically, that means that because we've got a lot of warm air in this system and
18:04we've got the winds pushing it against the hills across western Scotland, as that warm air is
18:10forced to rise over the hills it cools, condenses and all that moisture that originally came from
18:16the tropics drops out over the hills and mountains of western Scotland. So it's going to be a big
18:23difference between western Scotland's hills and eastern Scotland's rain shadows, you can see not
18:29much rain there at all but basically the rain turns heavier through the second half of Wednesday,
18:34continues overnight, further pulses coming through on Thursday morning, the winds picking up a bit
18:41of strength overnight Wednesday into Thursday and then as you can see the front sinks south and
18:47southeast, that fizzles out, very little rain for the Midlands, the south and southeast of England
18:54before the next system moves in. More on that in a moment, that's another system
18:59that we're keeping an eye on for the end of the week but let's take a look at the rain totals
19:04and I'm just going to put the 24-hour totals on, this captures most of the rain we're expecting to
19:10fall from the remnants of Ernesto and as you can see this is the 24-hour totals from 10 a.m. Wednesday
19:18to 10 a.m. Thursday and there's a real contrast across the UK, no rain at all for parts of the
19:24Midlands, East Anglia, the south and southeast but a lot of rain coming into western hills so
19:30but a lot of rain coming into western hills so the hills of Wales there we've got 25 to 50
19:36millimetres of rain, Cumbria in places a little more than 50, likewise for southwest Scotland
19:44but the largest rain totals from the remnants of Ernesto really picking out the hills of western
19:50Scotland there we've got Skye, Mull, West Highlands, Argyll and in places 150 millimetres perhaps a
19:58little more so that could cause localised flooding, could cause transport disruption and so on so a
20:05very wet spell basically throughout Wednesday and into the start of Thursday. Then while I'm
20:11on this chart looking ahead to I think, whoops wrong one, back to that one
20:24and
20:25that one, here we go, looking ahead
20:31to the middle of Friday that's the next system coming through, not quite as much rain but again
20:37it's western hills where we're likely to see 25 to 50 millimetres of rain, mostly 25-30 millimetres
20:43of rain from the next wet spell coming in through the day on Friday but this isn't going to contain
20:49quite as much moisture as ex-hurricane Ernesto so really it's Wednesday into the start of Thursday
20:56that's the important period, there's the weather warning that we've got for western Scotland
21:02and so yeah a significantly wet spell impacts are likely from that amount of rainfall. Stay tuned
21:09to the warnings of course, website, app and so on could be refined further over the next 24 hours
21:15or so. Now I mentioned another potential wet spell, let's take a look at that,
21:19let's take a look at the bigger picture. After Ernesto's through,
21:27zoom out, what we're likely to see as Ernesto pulls away, merges into this front, is the jet stream
21:37or at least the remnants of Ernesto as it moves through, this wind push in the wake of Ernesto,
21:43push colder air in from Greenland and the Davis Strait there, you can see this pool of cold air
21:51and at the same time the remnants of the tropical moisture and warmth from Ernesto's, it's just a
21:57trail there across the Atlantic so we've got this cold air that's coming through,
22:03cold air coming south, we've got this tropical warmth left over from Ernesto and in between
22:13this sharp temperature contrast and this is what I mean by feeling a bit more autumnal,
22:19the power on that jet stream coming in across the Atlantic, yeah you get this sort of thing in
22:25August of course, it's August where we're most likely to get a slightly stronger jet stream and
22:31deeper lows but it could be more indicative of an autumn-like pattern as well and this jet stream
22:39picks up this little feature, just a weather front on Thursday morning but playing it forward,
22:48that moves on to the cold side of the jet stream which allows it to spin up
22:53into a more active feature, some uncertainty about the track and depth of this low as it moves in
22:59on Friday but really it's during the early hours of Friday and look at that, early hours of Friday,
23:053am, got this strong jet stream across the UK, we've got this low deepening and we've got this
23:11spell of rain and wind moving in from the west so this is the next wet and windy spell, hot on the
23:17heels of the initial windy spell that I just mentioned and wind gusts are likely to be
23:26up and down through the week but certainly it's windier compared with much of summer so far.
23:31Here's Ernesto's winds and at first it's 50 miles an hour or so across western Scotland
23:37on Wednesday evening, there's another sway, the very strong winds that moves into the Irish Sea
23:43on Thursday morning so waking up Thursday across Irish Sea coasts and potentially the hills of
23:48northwest England, southern Scotland, north Wales, 50 to 60 mile per hour gusts so yeah if you've
23:56got holiday plans, outdoor activities, that sort of thing, north Wales, northern England, southwest
24:02Scotland, not looking good first thing Thursday. That system then moves through, then calms down a
24:09little bit but it's still a blustery day on Thursday before the next system comes in,
24:15here it comes, wind gusts pepping up a little bit more, not quite as much but still yet a few places
24:21getting 50 mile per hour wind gusts there, north Wales, early Friday, northern England there and
24:26then it moves out into the North Sea. So we've got some very wet weather especially western Scotland
24:33then we've got some very windy weather, 50, 60 miles an hour for the time of year, windy weather
24:38on Thursday morning and Friday morning before eventually things start to change once again
24:47heading into the weekend. It's not going to be an overnight change, there's still some
24:51unsettled weather to talk about at first this weekend which of course is a bank holiday for
24:55England, Wales and Northern Ireland but let's take a look at the bigger picture first of all
25:02for the bank holiday weekend. Now we've got Friday, that low moving away followed by frequent
25:11showers across northwestern parts of the country and then as this cold front pushes southeast
25:20what you can see Friday evening is this little wave developing on it, that's where the front
25:25is more or less parallel with the winds and it just sort of bulges north again and so rather
25:32than a cold front clearing it pushes back into the south and southeast of the UK. On Friday night
25:39and into Saturday there's some uncertainty about the extent to which that warm front will push
25:44rain back north across the UK. Here's what the latest Met Office model is showing and
25:51this is 5am Saturday, just rewinding a little bit and you can see the nature of some of that
25:56heavier rain on Friday night across the south of the country. Showers for western Scotland,
26:01Northern Ireland, Irish sea coastal areas, Wales and so on but yeah it's this bulge of heavier
26:07rain that could just turn up overnight Friday and take its time to leave southeastern parts
26:13on Saturday. These waving fronts, they're very tricky to forecast, they tend to linger,
26:22they're parallel with the wind so they're not moving on very quickly at all. So this is as we
26:27wake up on Saturday, could be some wet weather around for East Anglia in the southeast, for
26:31London, Southampton and so on. Bright spells of showers towards the west and the north
26:37and just to give you an idea of some of the uncertainty on that weather front, this is
26:42this is called a spaghetti chart. You might not be able to see the UK
26:47on the screen there, it's quite faint but there's the UK just pointing out there.
26:52It's called a spaghetti chart because the weather fronts that are modelled on it basically look
26:57like spaghetti, colourful spaghetti. And what you can see is that each of these lines is a
27:04projection from a certain model when we run the model 50 times and those model projections put
27:11the weather front in slightly different places. A lot of them have it, this is midday Saturday by
27:15the way, a lot of them have that weather front clearing into the continent but some of them have
27:18it just hanging back across East Anglia and the southeast. While we're talking about spaghetti
27:24charts I've got another one to show you for the end of the bank holiday weekend. This shows
27:28midday on Monday, most of the UK not covered by weather fronts but we've got this cluster
27:35of lines out to the west and this shows the position in 50 or so different model simulations
27:42of a warm front. So in between the cold front clearing Saturday, the southeast, and this warm
27:50front moving into the west and the northwest later Monday, there aren't really any significant
27:56weather fronts to talk about for the bank holiday weekend. Instead we've generally got the jet
28:02stream sitting to the south of the UK and a mix of bright spells and showers so yeah it's not
28:10going to be heatwave this bank holiday weekend, it's not going to be hot and sunny and dry everywhere
28:16but it's not going to be a washout either. So this is Saturday, once that rain finally does clear
28:24it's basically a mixture of bright spells and showers with the most frequent and most blustery
28:29downpours across northwestern parts, could be some thunderstorms here. And then into Sunday,
28:35further showers to come especially again in the west and the northwest but plenty of bright spells
28:40in between. Monday starts that way, perhaps mostly dry across the country before that weather front
28:46moves into the northwest by the end of the day but it looks most likely that we'll be at the end of
28:52the day that that weather front will move in and then spread across the country during Tuesday,
28:57although Tuesday as that weather front sinks south, looks like that weather front might not
29:03sink all the way south and it could just weaken and fizzle out because after that, talking about
29:10different weather patterns and different phases through the summer, we could be into a slightly
29:14different phase again through next week. The final week of summer is looking something
29:22more like, I thought I had a chart in here to show you what it looks more like but I didn't
29:26put it in there. I'll try and paint a picture in your minds instead. Basically it looks more like,
29:32let's bring a map up, low pressure, this is the most likely weather pattern from Tuesday onwards
29:40next week until the end of summer, low pressure to the northwest, somewhere like that, of the UK,
29:46higher pressure to the east. In fact Tuesday's already at the time of recording showing something
29:53like that but we'll go to the very end there and what you can see coming out the Atlantic is this
29:58next low but the jet stream at the same time is becoming a bit more wriggly again, a bit weaker,
30:04not quite as autumnal looking. So what looks most likely is this low will sit to the northwest of
30:09the UK and we'll see a ridge of higher pressure over the east of the UK and in that kind of
30:17weather pattern for the last few days of summer it's likely to be drier, less windy and warmer
30:24overall compared with the next few days. But the biggest temperature anomalies, the biggest dry
30:30anomalies are likely to be towards the south and the southeast. It's likely to be still more cool
30:36and changeable towards the northwest, so western Scotland, Cumbria, Northern Ireland, that sort of thing.
30:40So that's how the last few days of summer are likely to play out. Low pressure to the northwest,
30:47still some influence there into the far northwest. Higher pressure to the east,
30:52a warmer feel for many parts of the UK. Temperatures a little above average although
30:57it doesn't look like a heat wave is imminent. Lots of stuff I've just discussed there. Hope it all
31:06made sense but if it didn't, fire me a question in the comments. I'll try my best to answer it
31:11and yeah that's probably enough for me for this week. I'll let you all go. Thank you for watching
31:16once again and don't forget to hit like, hit subscribe so you never miss an update. Bye bye.