The mercury is rising this week and the humidity is too, some parts of the UK will experience exceptional temperatures. It won’t be sunny everywhere however as the heat and humidity will also trigger thunderstorms. Alex Deakin explains.
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00:00Hello. During the next 10 days, many a summer school holiday will begin, and that can seemingly
00:08coincide with a change to wetter weather. Now, that's kind of true. This year, we are
00:13going to see some wetter weather, certainly through the rest of this week, especially
00:17so on Friday and Saturday. But if you're after some finer weather, well, over the next four
00:22or five days, Sunday is probably your best bet. Next week, however, well, there's a bit
00:28of uncertainty, but there are some signs of some hotter weather on the way. But it's
00:34not going to be everywhere that sees the hotter weather, only some parts of the UK. We'll
00:39have a look at that in just a moment. But first of all, let's deal with the shorter
00:43term. And yes, some wetter weather on the way. Some welcome rain across the south where
00:47it has been very dry. One area of low pressure bringing a bit of rain on Wednesday and Thursday.
00:53But this one in particular, driving in on Friday is going to provide widespread rain
00:59through Friday and into the weekend. And some of that rain could well be on the heavy side
01:04too. As I said, welcome rain across England and Wales where it's been a dry July so far,
01:08but not welcome if you're hitting the roads. As many people will be on Friday, there'll
01:13be a lot of surface water and a lot of spray around. Spell of rain moves through and then
01:17heavy thundery downpours develop through Friday afternoon with the potential for some
01:23large hail as an extra hazard on the roads too. Now, that weather system moving in on
01:28Friday, as I said, bringing widespread rain tends to ebb away, but it's still controlling
01:34things into Saturday. Saturday is basically then a day of heavy showers breaking out across
01:39the UK. But look at this for Sunday. Just a little bump in the Isobarza, a brief ridge
01:44of high pressure settles things down. But looking at the bigger picture, there's more
01:48lows to then come in as we go into the early part of next week, probably bringing some
01:52rain even by the end of Sunday into the northwest. But the overall picture for the weekend is
01:58heavy showers likely on Saturday. They'll be hit and miss. It won't rain all day, but
02:02there could be some big downpours around. No, if you're after a dry and a bright day,
02:07Sunday looks like a decent bet, certainly for a large part of the country. OK, what
02:12happens after that into next week? Well, for that, we need to take a look at the bigger
02:18picture and take a look at what's going on high up in the atmosphere and the jet stream.
02:22Now, this is the position of the jets. Nothing too strong about the jet coming across the
02:26Atlantic, driving that weather system in through the weekend. But fast forward just to 36 hours
02:33or so and the jet has shifted. And the UK is no longer on the northern side of it. But
02:38by Sunday and Monday, we're on the southern side of the jet in this ridge, this little
02:44amplification of the jet. And that means that high pressure is likely to be close to southern
02:49and eastern parts of the UK. But the jet is still driving low pressure systems between
02:54the UK and Iceland. So we're setting up this contrast into next week between the northwest
03:01and the south and the east. And the closer you are to the low pressure, the more likely
03:06you are to have outbreaks of rain. The closer you are to the high pressure, well, the more
03:10likely you are for fine, dry and sunny weather. But it's not just about the clouds and the
03:16rain. It's also about the winds. Tightly packed isobars close to that low to the northwest
03:21promise quite gusty conditions here at times, certainly through the early part of next week.
03:26Whereas further south, close to the high, the isobars further apart, the winds will
03:29be lighter. But perhaps more importantly here, the direction of those winds going around
03:35the high pressure like this and potentially therefore wafting up some warm air, maybe
03:42even some hot air coming up from Spain and France once more into next week. As I said
03:48at the start, there's a bit of uncertainty about the whole scenario as we go into next
03:53week. And the jet stream is playing a bit of a part in that. This is one of the computer
03:58scenarios for the middle of next week, the European computer model. This is the jet stream,
04:03slightly different look at it from compared to earlier. But basically, the jet stream,
04:06the strong winds, the yellows here still going up to the northwest, bringing low pressure
04:11to the northwest of the UK, high pressure of the near continent that would allow the
04:15heat to build across the south. This is the European model, but other computer models
04:19have a slightly different idea. This is the American scenario where the jet stream is
04:24in a similar position, but it has a bit more oomph about it and shifting through the UK,
04:29bringing a slightly different feel, bringing the low pressure more into the UK and shunting
04:34the high and the hot air more across Europe. So this is the scenario, if the American model
04:40is correct, looking at the temperature profile across the UK and the green, yellow colours,
04:46temperatures around or below average. But if we go back to that earlier scenario, the
04:50European computer model, if that's right, with a jet stream staying to the northwest,
04:54that could open the door to some hot air, the reds and the purples there moving up across
05:01certainly southern parts of the UK. But notice, even in this scenario, the northwest always
05:07stays with the cooler air. We'll have that big contrast between southeast where it could
05:12be hot and the northwest where it's cooler and potentially wetter. Now, this is the more
05:17likely scenario at the moment. So this does open the door to some hot weather across the
05:22south. But this, again, is just looking at one computer model. That's not always the
05:26best way to look at the forecast for the medium to long range. So what we also run is ensemble
05:33computer models where we run the same computer, but lots of different times with slightly
05:37different starting scenarios. I've shown these before. This is called a meteogram. This one's
05:42specific to Reading and it shows the timeline along the bottom, particularly focus on the
05:47red blobs. That's the likely maximum temperature in Reading as we go into next week. Now, it
05:54shows the cooling trend through the latter part of this week, but it also shows the most
05:58likely scenarios that these blobs all get above the average line here. So there's a
06:03good signal that temperatures will be rising next week across the south. But how much they
06:09rise? Well, that is the big uncertainty. And notice these blobs get really quite big by
06:14the time we get to Wednesday and Thursday next week, with some of the computer scenarios
06:19suggesting hot conditions, whereas a few of them also suggesting that temperatures are
06:24only just a bit above average. So what I'm showing you here is just that uncertainty
06:28as we go into next week about the extent of the heat. How hot will it get? And obviously,
06:34we have that uncertainty about where we're going to see that cooler air coming in. How
06:38much of the northwest will be influenced by the cooler weather and how much of the south
06:43and east will be influenced by the hot weather? So at the moment, yes, there is a likelihood
06:48that some parts of the UK will see a hot spell next week. The most likely area to see temperatures
06:55significantly above average is across the southeast. But there's a lot of uncertainty
06:59about the extent and how long it could last. It's not unusual to have this amount of uncertainty
07:06for a forecast 7, 8, 9, 10 days away. That's what this 10 day trend is all about. It's
07:11not giving details. It's just letting you know what we here at the Met Office, the experts
07:16upstairs are really focusing in for next week. And just that scenario, there is a possibility
07:21that some parts could see some hot weather next week. We'll keep up to date with the
07:26very latest details day by day. And the best way that you can keep up to date is by following
07:32us on social media.