10 Day Trend 10/07/2024 – Any signs of a change?
This is the Met Office UK Weather forecast for the next 10 days 10/07/2024.
The jet stream has been stubbornly sitting to the south of the UK recently. Any signs of a shift?
Bringing you this 10 Day Trend is Aidan McGivern.
The jet stream has been stubbornly sitting to the south of the UK recently. Any signs of a shift?
Bringing you this 10 Day Trend is Aidan McGivern.
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NewsTranscript
00:00Hello and welcome to the Met Office 10 day trend. British summers are notoriously variable
00:05from year to year with or without global warming. They always have been, they always will be
00:11and much of that variability depends on where the jet stream sits. And this summer so far
00:16the jet stream has been often defaulting to the south of the UK. That means the UK has
00:21been sitting on the cool side of the jet stream and we've often seen low pressure which normally
00:27sits to the north of the jet stream. Indeed at the time of recording an area of low pressure
00:32has been bringing some very unsettled weather, some unseasonably low temperatures and outbreaks
00:37of rain across much of the UK through Monday, Tuesday and into Wednesday. Now if you were
00:43to look at the model output from a few days ago the signs were relatively optimistic for
00:48later this week into the weekend. This area of high pressure would build in, the jet stream
00:53starting to push to the north of the UK and broadly speaking that is the theme over the
01:00next few days. But there have been some subtle shifts and the main shift has been that the
01:07jet stream is pushing even further north than previously thought and that amplification
01:15in the jet stream allows this area of high pressure not to topple in over the UK pushing
01:19the low over towards the continent and moving the south shifted jet stream out of the way.
01:26Well what's happening is that higher pressure is building further north, in fact to the
01:31north of the UK and that means that it doesn't topple in over the UK and doesn't move this
01:39branch of the jet stream out of the way and what we end up with on Saturday with this
01:46branch of the jet stream well to the north and unable to move this branch of the jet
01:51stream out of the way, what we end up with is something called a trapped vortex. So this
01:56circulation in the upper winds, the jet stream sitting on top of the UK and an upper area
02:03of low pressure in place for the weekend that's unlikely to move along for a couple of days
02:09and it then leaves a gap for this branch of the jet stream to move in for the start of
02:16next week bringing another low pressure and continuing the theme of the summer so far.
02:23So a subtle shift that's more amplified jet stream through the weekend means that the
02:29circulation over the UK, an upper area of low pressure is unable to move along and we
02:35keep things unsettled for the time being but not quite as unsettled at least for the
02:40next few days as we saw at the start of the week with some very wet weather during the
02:45last couple of days especially for the north east of Scotland. Now that's tending to fizzle
02:49out through Thursday morning although it stays grey and damp in places and there's another
02:53band of rain that's going to sit across central parts through Thursday as well. Some sharp
02:57showers across east Wales into the Midlands for example but to the south some warm sunny
03:01spells and for north west Scotland, Northern Ireland also some warm sunshine coming through.
03:07So drier and brighter for many but not for all on Thursday. Likewise on Friday well we're
03:13going to see the cloud and rain across central parts sink south overnight Thursday into the
03:18start of Friday and this area of rain moving to the North Sea so clearer spells for Scotland
03:23and Northern Ireland. A fresher night for many compared with recent nights but the chance
03:28of some heavier rain for a time in the south coast that originates over the continent and
03:33just well starts to move north for a time. Then into Friday itself it's likely that this
03:40heavy rain will be their first thing and it will come and go through the day increasingly
03:45focused towards the far south east whilst a zone of more unstable air affects the far
03:52south west. Meanwhile elsewhere actually a drier day albeit relatively cloudy, relatively
03:58cool for the time of year. Temperatures in most places mid to high teens, perhaps 20-21
04:04in the south. The air is coming from the north by this stage. One or two showers for northern
04:08Scotland as well, Northern Ireland but otherwise many places drier and brighter and you can
04:13see on the rain totals map this is the six hour accumulations through Friday afternoon.
04:19Very little rain across the country on Friday for a change but there is this area of rain
04:23over the continent and that could cause things to be quite soggy by the end of Friday in
04:29the far south east, some uncertainty about the extent to which that affects the south
04:32east and likewise I mentioned those heavy showers across parts of the south west and
04:37there is the risk of some very heavy rain for a time very locally across south western
04:43parts and you can see it's focused inland across parts of Cornwall so someone like Exmoor
04:48could see 50mm of rain or more in the space of six hours. But then heading into the weekend
04:55and on the face of it higher pressure is in control, that higher pressure sitting to the
04:59north and extending a ridge across the UK but I mentioned that trapped vortex, that
05:06circulation in the jet stream that's just stuck over the UK and this upper area of low
05:13pressure. So what happens when you've got a surface area of high pressure and an upper
05:18area of low pressure? Well effectively you've got a vacuum in the upper atmosphere and air
05:25rushing up to fill that vacuum. Essentially you've got rising air and some sharp showers.
05:31This is how Saturday afternoon looks, showers for many places especially towards the west
05:37but actually some places will avoid those showers and stay dry through the day, a lot
05:40of cloud cover and still relatively cool for the time of year. This is how the temperatures
05:44will compare to average on Saturday, it's especially cool towards the north east, several
05:49degrees below the July average. Fast forward to Sunday and temperatures are a little closer
05:53to average for the time of year. It's warming up slightly, it's certainly going to feel
05:57more humid in the south when the sun comes through, 23C or so, that's not far from average
06:02for the time of year, still relatively cool in the north east, still a lot of cloud on
06:06the map and still some showers. And what you will notice if you look further east is this
06:11spiralling band of cloud and rain in the computer model from the Met Office, well that
06:17shifted east but in other model output, for example on the American model and the European
06:23model shown in these two panels here, it's got that rain much closer to the UK. This
06:28is the total rain through Saturday and Sunday. Met Office model showing showers across the
06:34UK generally, that rain staying to the east but from the European and the American models,
06:40they have the rain much closer into the UK. We don't need more rain in the north east
06:45of Scotland of course, we've seen plenty over the last couple of days so hopefully we won't
06:49see too much more this weekend but it is looking slightly more likely, looking at the majority
06:54of the model output that we will see at least some rain, for example on Sunday, coming into
06:58north eastern parts of the UK rather than bright spells and showers. Either way, that
07:04is going to eventually move away and there will be a gap, brief respite for a time before
07:10Once more, the south shifted jet stream sends another area of low pressure in from the south
07:14west, like I say, continuing the theme of the summer. So far with the jet stream to
07:19the south, we are on the cool side. This is the most likely weather pattern for Monday
07:23the 15th of July, the halfway point of summer, St Swithin's Day and low pressure there to
07:29the south west. Outbreaks of rain or showers coming up from the south west, temperatures
07:34below average for the time of year. Fast forward to Tuesday, that low is moving through, still
07:39lots of showers, longer spells of rain and temperatures suppressed for the time of year.
07:44By the time we get to the end of the week, increased levels of uncertainty. Now this
07:49is coming up as the most likely weather pattern for Thursday the 18th of July. Higher pressure
07:53building across southern parts, lower pressure heading to the north, the jet stream heading
07:58to the north but there is an alternative scenario which is coming out as less likely and it
08:05is showing higher pressure kept at bay and still lots of showers and lower pressure over
08:10the UK. But by the time we get to Saturday, well that scenario is coming out as the most
08:16likely by this stage, higher pressure kept towards the south west, lower pressure over
08:22the UK, south shifted jet stream. Saturday is still showing this as a lower probability
08:28scenario, there is only a fraction of a percent difference in terms of those two scenarios.
08:35So which one do we believe? Do we believe the ridge of higher pressure extending in
08:39or do we believe briefly higher pressure before lower pressure and south shifted jet stream
08:45return? Well, on balance, given the computer model's performance through the summer so
08:51far, as meteorologists we would suggest following the more pessimistic scenarios, lower pressure
08:59more showery conditions. And that's because if you look at the outputs a few days ago
09:03for what the most likely pressure anomaly would be for next week, well they were showing
09:08that higher pressure was more likely to extend across the UK but then a day or two later
09:16and that higher pressure influence waned and it was saying lower pressure was more likely
09:22to start to come in from the west. And the most recent model output suggests lower pressure
09:29and that higher pressure much more diminished. So it seems, and this has been the theme of
09:34the summer so far, when the computer model suggests higher pressure, more settled weather
09:40in 7-10 days time, you get closer to the event and that signal tends to disappear. And the
09:47atmosphere seems to, at this moment in time, always find a way to default to lower pressure,
09:54jet stream to the south and so on. And so, yeah, we can hope for higher pressure and
10:01more settled weather if that's what you like. Not everyone does like it of course but we
10:05can hope for that. But expect, given the state of the summer so far, the opposite. Of course
10:13we'll keep you updated right here at the Met Office and make sure you subscribe to YouTube
10:16so you never miss one of those updates. Bye bye.