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