Deep Dive 01/08/2023 – Any signs of summer? – Met Office weekly weather forecast UK

Name: Deep Dive 01/08/2023 – Any signs of summer? – Met Office weekly weather forecast UK
Uploaded: 2023-08-01T14:15:14+00:00
Duration: 25 min 1 s
Channel: Met Office

00:00 Here we go in 5, 4, 3, 2...

00:05 Following the UK's hottest June on record,

00:09 some places have experienced their wettest July on record.

00:14 You could accuse the UK weather of being all sorts of things,

00:17 but one thing you can't accuse it of being is boring.

00:21 We're into a new month. What will August bring?

00:24 Is there any sign of more summer-like conditions?

00:28 Well, if you watch to the end of this week's Deep Dive,

00:31 it will almost be time for next year's summer. We could do it all again.

00:34 Only kidding. If you watch to the end of this week's Deep Dive,

00:37 I'll have some signs, some glimmers of hope

00:41 for something more typical for summer in the UK.

00:45 But no signs of anything particularly hot and prolonged sunny weather.

00:52 But let's start with the July stats,

00:55 because it has been a remarkable month,

00:58 particularly the difference in July following June,

01:02 which, as I mentioned, was the UK's hottest on record.

01:05 July, this is the rainfall anomaly chart for the month.

01:10 Provisional data has to be set at this stage.

01:13 And you can see a lot of blues on the charts,

01:15 which, as you can see from the key there,

01:17 anything that's blue is wetter than average for July.

01:22 And the darkest blues across Northern Ireland,

01:25 which has provisionally had its wettest July on record.

01:28 Also wettest July on record for parts of North Wales and North West England.

01:32 Some significant rainfall anomalies there for southern parts of England as well.

01:38 Not many whites on the charts, which would indicate average conditions,

01:41 and no browns. So nowhere has had a drier than average July.

01:47 As far as temperatures are concerned, it may have felt especially cool

01:51 given all the wet weather and the serious lack of sunshine.

01:54 But temperatures are perhaps surprisingly less anomalous

02:00 compared with rainfall amounts.

02:03 These two charts show the maximum temperature,

02:06 so the highest temperature recorded during the daytime.

02:09 That's the temperature anomaly there on the left.

02:12 And then the mean temperature,

02:14 so the average of the overnight and daytime temperatures.

02:17 Now the UK as a whole saw -0.8 Celsius in terms of its maximum temperature.

02:24 So days were almost a degree lower than normal.

02:29 And the biggest anomaly there was across, say,

02:32 south-east Wales into central/southern England, for example.

02:37 Quite a lot of blue on the chart.

02:39 Now, overnight temperatures were actually slightly above average,

02:43 probably because of the copious amounts of cloud that we had through the month.

02:47 And that means that the mean temperature for the month has been 0.3 Celsius below average.

02:53 So not record-breaking by any means, certainly a cooler than average month.

02:58 And actually, you only have to go back to 2020 to see a cooler July.

03:03 So it's only been the coolest July since 2020.

03:06 Incidentally, it's been the wettest July since 2009.

03:09 So we have had wetter and we have had cooler Julys in recent years.

03:14 But this July, certainly the contrast between what we experienced in July compared with June has been remarkable.

03:21 Now, the mean temperature for this July has been 14.9 Celsius for the UK.

03:26 And in June, it was 15.8 Celsius.

03:29 Normally, June is much cooler than July.

03:32 So we've seen this switch this year, which doesn't happen often.

03:36 It's relatively rare to have such a big temperature difference, in fact,

03:41 going from warmer than average to cooler than average in July.

03:46 And the reason for that, you might have guessed, the jet stream.

03:50 It has been often to the south of the UK.

03:53 We've seen much cooler air arriving from the northwest at times and very unsettled weather as well.

03:58 Low pressure after low pressure.

04:00 And if we just run through this sequence over the next few days, you can see Wednesday,

04:03 that jet stream still dipping to the south of the UK.

04:06 Into Thursday, this trough in the jet stream persisting over northern Europe.

04:11 This is the kind of shape of jet stream that we've had throughout July.

04:14 A big ridge in the Atlantic, a big trough in the jet stream over the UK.

04:19 And if we go out to the end of the week, really Friday and into the weekend,

04:23 that jet stream to the south or over the UK.

04:26 And that corresponds to often unsettled weather.

04:30 In fact, low pressure after low pressure will continue to arrive.

04:34 And it's this first low this week that comes along into Wednesday.

04:39 It's quite a deep area of low pressure and it's going to bring the strongest winds on the southern flank of the low,

04:46 which is often the case in the mid-latitudes.

04:49 And the tight isobars there, they're going to especially affect parts of northern France.

04:54 But they'll also bring some particularly unseasonable winds.

04:58 So some especially, well, disruptive winds to southern coastal parts of England.

05:04 Not the kind of winds that you'd normally expect in July and the kinds of winds that would bring more impacts in July

05:10 than they would necessarily in January because of people taking part in outdoor activities, of course,

05:15 people camping and travelling about a lot more.

05:18 So we've got the winds courtesy of this low crossing the country during Wednesday.

05:23 And then as that clears away, some heavy rainfall associated with it as well.

05:27 Rainfall ahead of the low and then some lively showers behind it.

05:31 So a number of weather warnings at the moment for Wednesday.

05:34 And let's just take a look at those warnings.

05:38 And there we go. Put them on the map there.

05:41 The wind warning in the south, that's because of, as I mentioned, the unseasonable winds,

05:47 the risk of 45 to 50 mile per hour wind gusts across southern coastal counties of England.

05:53 Really it's coastal areas where we're going to have the brunt of this windy weather.

05:58 It will be much less windy inland.

06:00 And in some exposed spots, the risk of 60 or even higher mile per hour wind gusts,

06:06 especially around the Isles of Scilly, exposed parts of Cornwall, for example,

06:09 then later along other English Channel coasts.

06:13 This across central areas is a thunderstorm warning and that's also been issued for Wednesday.

06:19 And that details the risk of slow moving thundery showers, hail, lightning,

06:24 and the risk of 40 millimetres in a couple of hours.

06:27 And that could cause disruption.

06:29 Again, people travelling about, the greatest risk of disruption is on the roads, I think, on Wednesday afternoon.

06:35 So those are the two warnings we've got for the unseasonable weather on Wednesday.

06:39 Let's take a closer look at the weather charts for the next few days.

06:43 Now Tuesday is a reasonable day for many. It's nothing spectacular.

06:47 We've still got some slow moving showers across southern counties of England

06:51 and some outbreaks of rain across northern England and southern Scotland, turning more showery later.

06:56 A lot of cloud on the chart, but you can see there the first signs of Wednesday's weather

07:01 arriving from the south-west and fast-forwarding a few hours.

07:06 And that sweeps in really into the evening overnight, bringing a spell of rain overnight into England and Wales,

07:11 pushing into Northern Ireland and then clearing only slowly across southern Scotland and northern England into Wednesday.

07:18 But then, as that clears, we've got these slow moving showers.

07:24 So let's pause it there and you can see the distribution of the showers.

07:27 Just about anywhere could see showers on Wednesday, but it's really across - let's go back a few hours -

07:35 it's really across this central swathe of Wales into parts of the Midlands and East Anglia,

07:41 where the risk of these downpours is greatest.

07:44 You'll notice a more persistent rain there on the south side of the low, but that's carried through with strong winds.

07:51 Also, the more persistent rain driving in from the North Sea across south-east Scotland into north-east England

07:56 and some showers for northern Scotland, northern Ireland, south-west Scotland, for example.

08:01 But the brightest colours there are really associated with the heaviest showers into Wales, parts of the Midlands and East Anglia.

08:10 So we're talking hail, lightning and some torrential rain in places.

08:14 Always, as is the case with these showers, hit and miss.

08:17 Not everywhere will be affected by the worst of the impacts, but certainly the impacts likely through this swathe,

08:23 that's where the warning is, and surface water flooding, tricky driving conditions and so on.

08:29 Meanwhile, further south we've got those strong winds.

08:32 Let's just bring up the wind gust graphic because that will help us see where those strongest winds are located.

08:39 Rewinding a little bit back there, this is dawn on Wednesday.

08:44 That's when the strongest winds push into the Isles of Scilly, into Cornwall.

08:49 Playing that forward then.

08:51 You can see really how this colour here, that's associated with 50-60 mph wind gust.

08:57 Later in the day that clears through and the weather does tend to improve if you prefer drier and less windy weather.

09:06 For Thursday and Friday, and Thursday again as that low moves away, we've got this northerly airflow.

09:13 Bright spells and showers really through Thursday.

09:16 Quite a number of showers on the map by the afternoon, just about anywhere.

09:19 Scattered showers, again some heavy downpours at times, but they're going to be moving through quite quickly on this northerly airflow.

09:26 A lot of cloud developing by the afternoon after a bright start in places.

09:30 And then skipping forward to Friday and those showers are still quite prevalent across the UK, especially early on.

09:38 But then into the afternoon the showers become more and more focused across eastern areas.

09:43 And there's some concern with what the models are showing up for eastern parts of England.

09:48 For example, on Friday afternoon could be some slow moving showers and thunderstorms by this stage.

09:54 And given the wind direction, the winds coming down the North Sea from the north and then coming across the land, those winds could converge.

10:03 This is often the case when you get north.

10:06 You find that the winds over the land are a bit slower and change direction slightly.

10:11 So they come in more of a north-northwesterly, whilst the winds over the North Sea are coming down from the north.

10:16 And as a result they tend to pinch together, they tend to converge.

10:19 And as those winds are converging you get this uplift and you get this intensification of the showery activity into zones.

10:26 So into lines. Some places will see shower after shower and some impacts as a result.

10:31 Other places not seeing many showers at all.

10:33 And always the driest and brightest weather will be towards the west.

10:36 Wales, Western Scotland, Northern Ireland, South West England seeing some decent sunny spells by the afternoon.

10:42 But still, it's going to be cool. We've got this northerly airflow.

10:46 We're going to see some temperatures over the next few days because although Tuesday afternoon's temperatures are close to average for the time of year,

10:55 they are going to struggle into Wednesday.

10:58 Having said that, we've got a bit of humidity wrapped up in the low pressure that's moving through on Wednesday.

11:04 So the values here, 19, 20, 21 Celsius, are fairly wide, widely and typical of what we expect generally.

11:13 Could see a bit of brightness in between the heavy downpours across central areas.

11:16 And if that happens, the temperatures may be boosted locally by a couple of degrees compared to what we've got on the chart there.

11:23 A bit more of a humid feel.

11:25 Then into Thursday, again those temperatures down compared to the average for the time of year because of the northerly airflow.

11:33 So high teens, 20, 21 Celsius. You'd normally expect a degree or two higher than this for the start of August.

11:39 And into Friday, 18 Celsius for Norwich. That's significantly below average for the time of year.

11:46 18 Celsius for Plymouth there. 16, 17 for northern Scotland.

11:51 And into Saturday, we're still seeing those below average temperatures.

11:56 I'll show you that on a map point of view because we're not the only ones that are going to see below average temperatures this week and next.

12:05 These are the temperature anomalies from the European models from lots of different computer model runs.

12:13 But this is an average over Europe. There's the UK. There's much of central Europe.

12:17 And we've got this trough in the jet stream. The jet stream's sinking south, like I mentioned.

12:22 And that continues into the start of next week.

12:25 And you can see the blues there and the deeper blues across central parts of Europe.

12:30 So actually significantly below average temperatures, perhaps something to be celebrated for the likes of Italy and Spain, where we saw such intense heat more recently.

12:40 But yet the higher temperatures shifted further east across eastern Europe into Russia.

12:45 And this lower than average temperature regime persisting across central and northwestern Europe, at least into next week.

12:56 What are we talking about next? We've covered the rain on Wednesday, Thursday, Friday showers, jet stream.

13:02 Let's take a look at that because some interesting things happen approaching the weekend.

13:07 As I mentioned, the jet stream stays close to or to the south of the UK throughout the next few days.

13:14 But at the same time, some curious things are happening on the other side of the Atlantic.

13:19 So this is the time recording, Tuesday afternoon. We've got a weather system here over the northwest Atlantic.

13:28 And actually, if we run that forward, I think another one will start to emerge as well.

13:33 Or at least the site might not be that. Here it is, another one emerging there.

13:38 A couple of low pressure systems, essentially. And these contain some tropical warmth.

13:45 Let's rewind back to Wednesday. And the tropical warmth helps to push the jet stream on the other side of the Atlantic north.

13:53 Helps to amplify the whole thing, like cracking a whip. The jet stream gets pushed to the north.

13:58 And this ridge develops in the Atlantic. But of course, that has downstream implications on the UK.

14:04 This trough in the jet stream occurring over the UK, which is, as I mentioned, helping to lead to, A, some lively showers on Thursday and Friday.

14:14 And B, those much cooler than normal conditions across central and northwest Europe this weekend and into the start of next week.

14:22 But at the same time, those two lows I mentioned, they're lined up here.

14:27 And they're about to be carried by the jet stream and spun up into much deeper systems, or at least one of them is, for the start of the weekend.

14:38 The different computer model runs have played these out in different ways during the last few days.

14:44 There had been some quite deep solutions for the first low pressure system, for example, in the last couple of days.

14:53 Those models have generally eased off on the intensification of these lows, but they do deepen somewhat as they approach the UK.

15:00 This is just one computer model simulation, of course.

15:03 This is from the Met Office deterministic model, or the main model from the Met Office supercomputer.

15:09 And running this forward, you can see that as we approach the weekend, so Friday is a showery day with these northerly winds.

15:16 And then this first low gets picked up by the jet stream, starts to deepen.

15:22 And by the time we get to Saturday, really, it just swings into southwestern parts of the UK.

15:29 We've got some stronger winds. We've got some heavier rain.

15:31 This is the jet stream picking it up. And there it is. We're gaining some isobars.

15:37 We're seeing some heavy rain associated with it.

15:39 And it just slides across southwestern and then southern parts of the UK.

15:43 So that's from the Met Office main computer model run.

15:47 But, of course, we run the computer model lots of times.

15:50 And in all these different simulations, the jet stream does slightly different things to the low.

15:57 And the low appears in slightly different positions relative to the jet stream.

16:03 And that makes big differences in terms of its depth and its track by Saturday.

16:07 And I'll show you a couple of examples of that right here.

16:11 So this is showing midday Saturday.

16:16 And we've got the isobars, the lines here and the wind arrows showing the low pressure in slightly different positions from two computer model runs.

16:25 The colours on the maps indicate rainfall.

16:28 And we've got the UK here on the left-hand side. Here's Scotland. Here's England. Here's Wales.

16:33 And the low pressure on the Europe. This is the main European model run.

16:39 The low pressure is over northwest France.

16:41 And much of the wet and windy weather is affecting northwest France with quite a few showers across the UK.

16:46 So that's from the European model run for Saturday afternoon.

16:49 Nothing too serious or bothersome for the UK from that.

16:53 Meanwhile, this is from the American model run.

16:56 And again, there's Scotland, there's England and there's Wales.

16:59 It might be obscured by a huge amount of rainfall that's coming in associated with this area of low pressure,

17:05 which is much deeper in the American model run and moves across Wales and into the Midlands.

17:10 So there's a positional difference.

17:13 The American model has it running across central parts of England and Wales.

17:17 The European model has it into northwest France. And there's a difference in the depth of the low.

17:23 Now, these differences, because of chaos theory, they're the result of very tiny differences over the next few days

17:31 in terms of how that low pressure is picked up by the jet stream and how it's spun up.

17:36 So tiny differences over the next few days then escalate because of chaos theory into much bigger differences by the start of the weekend.

17:43 And Saturday, at the moment, quite tricky to handle.

17:46 What we think, looking at many more computer model simulations, is that there'll be something in between these two solutions.

17:55 The low pressure mostly moving along central or southern parts of the UK.

18:00 The wettest weather perhaps affecting southern and central parts of the UK.

18:04 A heavy band of rain moving through, although nothing too disruptive being signalled strongly at the moment.

18:09 And the strongest winds affecting Irish Sea and south-western coast.

18:13 Again, the potential for another unseasonable wet and windy spell to spoil anyone camping or anyone's outdoor activities on Saturday.

18:24 Kind of weather that you don't normally like to see on the first Saturday in August.

18:29 But nothing particularly disruptive in terms of, I guess, overly heavy rainfall and so on.

18:40 But it's certainly, given the model differences, something we need to keep a very close eye on.

18:46 Now, I mentioned that it's turning colder over the next few days.

18:49 Let's take a look at that in a graph.

18:51 And this is for a central part of the UK.

18:54 And what this shows is various graphs with different weather elements.

18:58 This is for Leeds. On the bottom here, might be tricky to see, but on the bottom we've got the temperature trend over the next couple of weeks.

19:05 And what we can see is the red line here, close to 20 degrees really.

19:12 And then these boxes showing the forecast range of temperatures over the next few days.

19:16 And the red boxes are consistently below the red line.

19:20 In fact, they're increasingly below it, especially on Saturday, of course, when we've got that potential for wet and windy weather moving through.

19:27 Then, very gradually through next week, this signal for temperatures to return to average or slightly above average by the end of next week, both by day and by night.

19:37 So we've got significantly below average temperatures for the first seven to ten days of August.

19:43 That's what's being signalled. But then the mid to latter half of next week, there's this signal for temperatures to start to trend upward once again.

19:52 At the same time, we've got the wind speed forecast here, and you can see much windier than average.

19:57 The average line close to four metres per second.

20:01 And then we've got the boxes above the average generally, both on Wednesday, as can be expected, and into the weekend as well.

20:07 Those boxes staying above average before trending downward slightly into next week.

20:12 And likewise for precipitation, these boxes indicate the range of precipitation.

20:16 Quite wet weather over the next few days and then at the weekend again, but a trend downwards.

20:23 Why is that? Well, let's take a look at what some of the computer models are suggesting for beyond the middle to the latter half of next week.

20:34 I just want to highlight this chart, for example.

20:38 Once we've got this weekend's weather out of the way, whatever it does on Saturday and into Sunday, we've got a period of northerly winds into the start of next week.

20:47 That's why we've got the suppressed temperatures for the start of next week.

20:51 But eventually there's this signal. This is for next Thursday.

20:56 And this is the most likely weather pattern for next Thursday.

20:59 There's this signal for higher pressures to start to move in from the southwest.

21:05 Now, there are still some colourful rainfall indicators there for Western Scotland, North West England and Northern Ireland in this likely weather pattern.

21:16 And that's because what we're seeing an indication for is for the jet stream to push a bit further north, for higher pressure to develop further south,

21:25 and for the wettest and windiest weather to be towards the northwest, and for the drier and brighter weather to be towards the south.

21:35 So certainly not a UK-wide or extensive hot spell or anything signalled in the models.

21:43 But what is signalled is a subtle change from the very unsettled weather that we've seen over the last few weeks,

21:51 the cooler than average conditions that we're going to see over the next week,

21:55 and the very wet and sometimes windy weather, to more typical weather for the time of year.

22:01 And I think a change to more typical weather for the time of year, given what we've just been through,

22:08 the very wet and slightly cooler than average conditions that we saw through July and what we're expecting over the next week,

22:14 a change to more typical August weather would feel like a vast improvement if you like dry and warmer weather this time of year.

22:24 Final two charts I'm going to leave you with, and these basically act as a proxy for surface pressure.

22:32 And the blues on the chart show where typically you'd have lower than normal pressure,

22:38 and the oranges show where you'd have typically higher than normal pressure.

22:43 The one on the left is for next week, and the blue there is to the east of the UK.

22:51 Now, the same chart for this week shows the blue right over the UK, this trough in the jet stream.

22:57 And what you can just about do is you can make out that the jet stream is shifting to allow this change in the distribution of lows and highs.

23:05 And we've got the dip in the jet stream moving to the east of the UK.

23:09 That's what's signalled for the middle to latter half of next week.

23:15 And the jet stream starting to ridge over southern parts of the UK to allow higher pressure.

23:22 And likewise, this shows the following week. So this is the middle of August.

23:27 And there's not really anything of note over the UK.

23:32 We've got a signal for something to do with higher pressure to the north of the UK,

23:37 and likewise over the Mediterranean. In between, the whites indicate neither lower nor higher than normal pressure.

23:44 Now, that could be a function of all the different computer models saying different things,

23:48 and so it averages out at no anomaly whatsoever. Or it could be that we're expecting something closer to average.

23:56 So I think what we're suggesting is through next week, the weather begins to become drier and warmer.

24:06 But it won't be a lengthy, dry and hot period with no rain whatsoever.

24:13 It just looks like the drier spells will be slightly longer than we've seen.

24:17 Temperatures will edge upwards back to around average for the time of year.

24:21 There'll be a better chance of seeing some sunshine at times.

24:24 And the most changeable weather will be shifted towards the northwest of the UK,

24:29 with the driest weather expected towards the south.

24:33 So through the next couple of weeks, perhaps a return to normal.

24:37 But normal at the moment would feel like a marked improvement compared with what we've seen recently.

24:45 That's all from me this week. I hope you've enjoyed it. I hope you found it useful.

24:49 If you do enjoy these deep dives, don't forget to hit subscribe, hit like, ask us questions.

24:54 We're always open to new ideas. But that's all I've got for you this week. Thanks for watching. Bye bye.

24:59 Bye-bye.

24:59 [BLANK_AUDIO]

Deep Dive 01/08/2023 – Any signs of summer? – Met Office weekly weather forecast UK

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