10 Day trend - A lively week and a half with some uncertainties 25/09/19 - video Dailymotion

Met Office

The next 10 days will bring further active weather systems across the country. Heavy blustery showers will be interspersed with some Autumn sunshine. There are a couple of uncertain areas in the longer range forecast, Alex Deakin has a closer look.

Transcript

00:00Welcome along to the Met Office

00:0110-day trend.

00:03The 10 days that promise some

00:05fairly lively weather.

00:06There are a few elements of

00:07uncertainty.

00:08It kind of breaks down into four

00:11time zones, really.

00:12The next few days, fairly

00:13straightforward.

00:14There'll be some sunshine.

00:15There'll be a lot more blustery

00:17showers.

00:18Bit of a question mark about sun

00:19there. Spell of wet and windy

00:21weather is likely, particularly

00:23in the south.

00:23But there is uncertainty about

00:25the track and intensity

00:27of the low pressure bringing

00:28that wet and windy weather.

00:29And then it may turn a bit

00:30cooler, particularly across

00:32northern Britain through the

00:33early part of next week.

00:34And then things get pretty

00:36complicated right at the end of

00:38next week, as we shall see in a

00:40moment.

00:41First of all, though, let's deal

00:42with the relatively easy spell

00:44of weather over the next three

00:45or four days.

00:46Easy, but it's not looking

00:49pretty out there.

00:49Low pressure is the dominant

00:51feature.

00:51It'll send spirals of showers

00:54across the country through

00:55Thursday, Friday and Saturday.

00:57The ice bars always close

00:59together across the southern

01:00half of the UK.

01:01So that's where it'll be

01:01windiest, which means the

01:03showers will move through.

01:04Further north, close to the

01:05centre of the low, the ice

01:07bars are further apart.

01:08The winds will be lighter, which

01:09means particularly by Saturday,

01:10the showers will be quite slow

01:12moving and possibly heavier

01:14and thundery.

01:15Notice there is another area of

01:16low pressure just waiting in the

01:17wings. More on that in a moment.

01:19But certainly, yes, the next

01:21three days or so, it's some

01:22sunshine, yes, but also plenty

01:24of heavy showers, often quite

01:26gusty in the south.

01:27But the winds coming in from the

01:28Atlantic, not particularly

01:30chilly, temperatures by day

01:32around or a touch above average

01:33and the nights certainly looking

01:35fairly mild.

01:36Then the big uncertainty comes

01:38at the weekend for Sunday's

01:40weather chart.

01:41This area of low pressure, what

01:43we saw earlier, will be

01:44approaching. It will bring some

01:45wet and windy weather, but the

01:46exact position and the exact

01:48timing still open to doubt.

01:50Now, it's really important this

01:51area of low pressure because

01:53with the ice bars squeezing close

01:55together, you can imagine that

01:56could bring some strong winds.

01:58Especially important this

01:59weekend because the tides are

02:00very high.

02:01Some of the highest tides of the

02:03year through this weekend and

02:04with low pressure and

02:06strong winds could emphasise

02:08and exacerbate some problems

02:10at coast. So there is the risk of

02:12some coastal flooding as this low

02:14moves in. But the timing, whether

02:15it coincides with the highest

02:17tides and the exact position of

02:19the low and the direction

02:21of the winds will be crucial.

02:23Now, this is just one computer

02:25model. This is the Met Office

02:26computer model charting for

02:27Sunday. But when we get to

02:29medium and longer range forecasts,

02:31we don't just look at one

02:32computer model. We have a few

02:33different computer models and we

02:35don't just run them once.

02:36We run them several times.

02:38And that's what I'm going to show

02:39you now to show the uncertainty

02:41for Sunday.

02:43This is called a Dalmatian plot

02:44for obvious reasons.

02:46This is the European models

02:48chart for Sunday, the Dalmatian

02:50chart for Sunday.

02:51And don't worry too much about the

02:53detail. But what I'm showing you

02:54here is just the uncertainty

02:56in the position of these spots.

02:58Each of those spots is an area

02:59of low pressure. So that low that

03:01we saw earlier by running the

03:02model lots of times could be

03:04almost any of these positions

03:06as it crosses the country.

03:08So I'm just showing you the

03:09uncertainty, the spread, if

03:11you like, of the different

03:12possible outcomes for Sunday from

03:14the European model and the

03:15different colours represent the

03:16different intensities.

03:18Again, you can see there's quite

03:20a range there.

03:21So there's a lot to be played for

03:23on Sunday. But the main themes are

03:24that the low pressure is likely to

03:26be across the southern half of

03:28the UK.

03:29And this chart is representing

03:31that in the rainfall

03:33amounts, the probability of

03:34rainfall amounts for Sunday,

03:36the probability of seeing heavy

03:37rain and the greener colours,

03:39a greater chance of that.

03:41So you can see that it's across the

03:42southern half of the UK where

03:44we've got highest chance of seeing

03:45some heavy rain on Sunday,

03:47whereas further north, a greater

03:49chance of staying dry.

03:51So some uncertainty about the

03:52timing and the intensity of

03:54that low, but it will, it looks

03:55like, bring a wet and windy spell

03:57certainly across the south sometime

03:59during the weekend.

04:01What happens beyond that?

04:02Well, that low pressure should be

04:03scooting away.

04:05As it does so, well,

04:06a couple of things. Notice the

04:07isobars are still pretty close

04:09together, so there could be some

04:10strong winds down the eastern side

04:12and with the tides still high.

04:14That is something we need to keep a

04:15close eye on, but also the

04:17direction of the wind coming down

04:18from the north bringing colder air

04:21as that low clears away.

04:23So there are signs that, yes, it may

04:24well turn quite a bit cooler

04:27through the early parts of the new

04:28working week, but how

04:31long that cold air stays,

04:33how far south it gets is open to

04:34doubt because there's another area

04:36of low pressure which will cut off

04:38that cold air and bring in some

04:40warmer and more moist air from

04:42the Atlantic.

04:43So it's a bit of a battleground the

04:44early part of next week.

04:45It looks like it could turn a

04:47little colder, particularly so

04:48across the north, whereas in the

04:50south, well, it may turn colder for

04:51a time before further outbreaks

04:53of rain spread in.

04:55So that covers the first half of

04:57next week, pretty much in that

04:58scenario.

04:59What happens after that?

05:00Well, as I said at the start, it

05:02gets even more complicated

05:03thanks to what

05:06is currently a hurricane, Hurricane

05:08Lorenzo.

05:09It's way out in the Atlantic, not

05:11really near any land at the moment,

05:13but in a week's time, it could be

05:15drifting a little bit further north.

05:17There's always a lot of uncertainty

05:19when we deal with hurricanes or

05:20ex-hurricanes as they will be

05:21approaching the United Kingdom.

05:24This is, again, a European model

05:25scenario for next Thursday.

05:27The black lines, the surface

05:29pressure chart, you can see a deep

05:30area of low pressure.

05:31That is what's left of Hurricane

05:33Lorenzo at this stage.

05:34The yellow, well, that's the jet

05:36stream. Why am I showing that?

05:38Jet stream usually drives

05:40areas of low pressure.

05:41That's how we describe the

05:43jet stream.

05:44But sometimes, particularly when

05:46you have a highly energetic

05:48system like an ex-hurricane,

05:50well, that can affect what's going

05:52on higher up in the atmosphere.

05:54And in this scenario, the European

05:55model for next week, it looks like

05:57what's left of Hurricane Lorenzo may

06:00affect the jet stream, pushing it

06:01further north.

06:03But that's just one computer model.

06:04Another one has a similar

06:06scenario for the same time zone,

06:08but some subtle differences.

06:10Here, Lorenzo is a little further

06:12south and it's not really

06:13interacting with the jet stream.

06:15The jet stream is staying further

06:16north and powering further areas

06:18of low pressure across the UK.

06:21So just an idea, flavour

06:23for combinations that could

06:24happen towards the back end of

06:26next week.

06:27We could see that area

06:29of low pressure that was

06:31Hurricane Lorenzo bringing its

06:33energy, interfering with the jet

06:35stream, pushing the jet stream

06:36perhaps further north.

06:37We call this amplifying the pattern.

06:39And in this scenario, that would

06:41allow high pressure to build across

06:42the UK, calming the weather down

06:44for the end of next week, perhaps

06:46bringing some sunshine, misty and

06:48cool mornings.

06:49But wouldn't take much.

06:51Subtle shift in that

06:53area of low pressure, not

06:55interacting with the jet stream.

06:57The jet stream continues to track

06:58across the UK and will continue to

07:00see further spells of wet

07:01and windy weather.

07:03So, yes, a lot of uncertainty about

07:04the end of next week.

07:06Nothing unusual about that,

07:08but it'll be certainly fascinating

07:09to track and see what happens with

07:11that ex-hurricane.

07:12Best way for you to stay up to date,

07:14of course, is to follow the Met

07:16office on social media.

10 Day trend - A lively week and a half with some uncertainties 25/09/19

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