Week Ahead 02/09/2024 – Big uncertainties ahead
This is the Met Office UK Weather forecast for the week ahead 02/09/2024. The jet stream dive south over the UK this week, allowing a cut-off circulation to spin off in the vicinity of the UK. But where this cut-off circulation ends up is very uncertain... as Aidan McGivern explains.
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00:00Hi there and welcome to the Met Office forecast for the week ahead. Some weather forecasts
00:05are more uncertain than others and this forecast for the week ahead unfortunately is one of
00:10the more uncertain ones. From Thursday onwards the jet stream starts to do interesting things
00:15in the vicinity of the UK and how that plays out will have consequences for Thursday, Friday
00:21and into the weekend with a number of different scenarios coming up in the computer modelling.
00:27More on that in a moment and for the time being the jet stream is diving south just
00:32to the west of the UK and ahead of this we've got warmth and humidity moving north across
00:38the country and certainly for the first couple of days of September it has been fairly humid
00:44in many places and with that humidity we've seen relatively high temperatures, 30 Celsius
00:49in the south east on Sunday but also a good deal of cloud and outbreaks of heavy rain
00:55in places. We're going to see more of that sort of thing, the instability and the humidity
01:00on Tuesday 3rd September. So a lot of cloud cover to begin things across England and Wales,
01:04some showers first thing. The focus for the showers moves east through the morning and
01:08by the afternoon heavy downpours most likely across East Anglia and the south east. Perhaps
01:13a rumble of thunder or two in between the showers, actually some bright spells and certainly
01:18drying up for western England and Wales with some sunshine by the afternoon. Scotland and
01:23Northern Ireland meanwhile sees cloud and showery rain move in from the west along
01:27with fresher conditions so temperatures here 16 to 18 Celsius, still a humid feel towards
01:33the east and south east where we do get some sunshine breaking through, it's still going
01:37to feel quite sticky, not as hot as the 1st and 2nd of September in places however. And
01:43the fresher air I mentioned there in the north west will move across the whole of the UK
01:47on Wednesday, a fresher feel for everyone. And with the jet stream diving south but that
01:54trough in the jet stream lying directly over the UK, well what we've got in the upper atmosphere
01:59is rising air and that means that we're going to see plenty more showers developing. Yeah
02:04there will be some sunshine and the showers will move through so it's not going to be
02:08a washout on Wednesday. Some places will see reasonable dry and bright spells but yeah
02:14there will be a lot of showers around and some of those showers will be heavy where
02:18they occur. But temperatures well up to around 20, 21, 22 Celsius in the south east again
02:24mid to high teens further north west but with a fresher feel. Lower dew points that means
02:29it won't feel quite as humid. Now into Thursday and Friday this is where the uncertainty really
02:35notches up because there are a number of different scenarios playing out in the computer modelling
02:41and I'm just going to describe the most likely scenario and then I'll take a look at the
02:45other possible scenarios. So this is the most likely scenario and we'll see further showers
02:49from this scenario across central and southern parts of the UK on Thursday, perhaps some
02:55longer spells of rain and where the showers are heavier we're likely to see some thunderstorms
03:00as well. Elsewhere a lot of cloud particularly across the north east and some low cloud here
03:05that will make it feel cool but we're going to see increasingly humid air arrive once
03:10again from the east although this will be coming effectively from the south around an
03:14area of low pressure stuck over the continent over say northern France. That means the best
03:20of the weather on Thursday will be across western Scotland and northern Ireland. It's
03:24been a disappointing summer if you like warm and dry weather but actually Thursday and
03:30into Friday are looking reasonable for plenty of sunny skies here, the best part of the
03:34UK for settled weather in this the most likely scenario because Friday brings some more heavy
03:40rain across southern parts of the UK and potential for some longer spells of rain with
03:45this scenario as well as the weather front becomes stuck over southern counties. Further
03:50north, the further north and west you are basically the drier and brighter it will be.
03:54The wind is picking up strength around this area of low pressure that's sitting to the
03:57south of the UK so it could be quite blustery to the north and northwest but actually some
04:03reasonable dry and sunny weather and feeling warm in that wind because of the increased
04:08humidity. Now as I mentioned this is the most likely scenario but it's not the only
04:12scenario and the reasons behind the uncertainty are to do with a jet stream disruption that
04:17is likely to happen during Tuesday and into Wednesday and as you can see on Tuesday the
04:22jet stream is extending south, this trough in the jet stream lies over the UK but occasionally
04:28what we see when the jet stream extends so far south is that an enclosed circulation
04:33cuts off from the main flow of the jet stream and then like a spinning top it just spins
04:38around erratically and predicting exactly where it will end up is very tricky in the
04:44computer modelling. In this the most likely scenario that area of enclosed circulation
04:50in the jet stream cut off from the main flow sits over the south of the UK and northern
04:56France and that's where we get low pressure forming hence the showers and longer spells
04:59of rain in the south and drier towards the northwest. This isn't the only scenario coming
05:05out and it all depends on exactly where this cut off low in the jet stream ends up. Now
05:12there are some computer models that suggest it will be a little further east and if that
05:16happens it could only cause a glancing blow to the UK before moving away and allowing
05:21higher pressure to develop and move back in from the Azores and leading to more settled
05:26weather again more widely across the UK although some showery rain possible from the jet stream
05:31across the far north and northwest of Scotland. That's a 20% chance that it will generally
05:37be fine from Thursday into Friday and the weekend as the jet stream or the cut off aspect
05:43of the jet stream moves quickly away into the continent. Now another scenario that's
05:48coming through has the jet stream cutting off to the east of the UK but closer to the
05:53south of the UK and this would lead to more widespread unsettled weather across well not
05:57just the south but also northern parts of the country with higher pressure kept quite
06:02far to the northwest. But the most likely scenario, the 65% chance of this occurring
06:09as I've already described is for the jet stream to cut off this circulation to the south of
06:14the UK, low pressure to the south, mostly fine to the north with higher pressure building
06:20back in. So that's the most likely scenario. However, there are those alternative scenarios
06:25that are coming through and we'll be able to update you more fully on what's likely
06:30to happen and give you more details in the next couple of days. So keep watching us on
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06:41channels of course to get all the very latest. Bye bye.