This is an in-depth Met Office UK Weather forecast for the next week and beyond.
Storm Ashley hit the UK at the weekend having explosively deepened in just a day or so. How did it deepen so quickly?
Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
Storm Ashley hit the UK at the weekend having explosively deepened in just a day or so. How did it deepen so quickly?
Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:00Storm Ashley hit the UK over the weekend having explosively deepened across the
00:05Atlantic in little over a day. It came out of nowhere and became a very very
00:10deep low indeed. Why did Ashley deepen so quickly and are we likely to see a
00:14repeat in the next week or so? I'm going to be answering those questions in this
00:18week's Met Office deep dive. Welcome along. These can be found on the Met
00:23Office app and the Met Office YouTube channel. There are plenty of videos like
00:26this on the Met Office YouTube channel so if you haven't discovered them yet I
00:29do urge you to subscribe especially if you're a fan of the weather like we are
00:34and if you know any other fans of the weather do let them know. Before we talk
00:39about yet more wind and rain I just thought we'd take a moment to marvel at
00:44some fog. This drone footage of fog near Axminster was taken by my talented
00:51colleague Rich from his drone and you can see the moment at which the drone
00:56rises through a layer of fog close to the ground and transforms the view from
01:02this gloomy autumn day to bright blue skies. Absolutely stunning. So if you ever
01:08wondered when you're wandering about in the fog and thought how gloomy it was
01:12well it's not you don't have to go far sometimes to see the Sun coming through
01:17and to see the blue skies. And we'll see more of that sort of thing in some
01:22places on Wednesday morning with lighter winds and clear skies across East
01:28Anglia say parts of southeast England. Wednesday morning is the morning this
01:33week where we most likely see some dense and widespread fog. But otherwise we're
01:39back to talking about wind and rain and before I talk about more rain on the way
01:44in some parts of the UK let's just have a look at the satellite image from Storm
01:49Ashley because it really was quite a fascinating system as it deepened over
01:56the Atlantic. Now before Ashley arrived Friday we saw a different low pressure
02:01this is another low that was sitting over Iceland and brought this band of
02:06rain west east across the UK and some strong winds especially across northwest
02:10Scotland accompanied by high tides and of course we saw coastal impacts as a
02:15result. At this stage, this is 1 a.m. on Saturday, Storm Ashley is just a shallow
02:21area of low pressure essentially this wave of clouds so you can see what
02:26meteorologists call a cloud leaf. It looks like a leaf doesn't it in the
02:29satellite imagery. This bulge of cloud emerging and we'll just fast forward a
02:35couple of frames there and you can see it's starting to really explode in its
02:43development. Now explosive cyclogenesis that's the technical term obviously the
02:48term weather bomb has been commandeered by some tabloids to make the weather
02:52sound even more exciting and frightening but actually explosive cyclogenesis is a
02:58genuine meteorological term for areas of low pressure that deepen by more than 24
03:04millibars or hectopascals in 24 hours and certainly Storm Ashley met this
03:08criteria as it deepened during Saturday and I'm just going to scroll slowly
03:13through the satellite imagery you can see that low pressure center forming
03:17just by there and the trailing area of cloud with bands of rain heading into
03:22the UK putting the radar on there you can see the rain reaching western parts
03:26at this stage before during Sunday the strongest winds reached northwestern
03:35parts of the UK. So why did it explosively deepen across the Atlantic?
03:41Some of the clues lie in the type of cyclone type of area of low pressure
03:46that Ashley was and just give you a brief history lesson before I draw a
03:52pretty picture. Back in the early 20th century a group of Norwegian
03:58meteorologists developed a model of low-pressure systems in the northern
04:03hemisphere or North Atlantic by looking at surface areas of surface observations
04:09and what they realized was you get these big temperature contrasts across an area
04:13of low pressure and so they realized that there are these strong gradients
04:17that we now know they called them weather fronts basically and they came
04:24up the idea of warm fronts we're all familiar with this now having talked
04:28about weather fronts and warm fronts and occluded fronts and so on in
04:34weather broadcasts over the years they came up with the idea of a low pressure
04:37system having first of all a flat what we call a wave where you've got warm air
04:48pushing north and cold air starting to push south and as a result with the help
04:56of the jet stream eventually you get a more pronounced differential developing
05:06and a little circulation so let's draw that this circulation here with a warm
05:13front like that and a cold front so this is the development stage of an area of
05:18low pressure and then eventually what the Norwegian model says is that the
05:25cold front overtakes the warm front or catches up with it and you get I haven't
05:33got purple that's annoying didn't think this one through I've only got three
05:37colors to choose from let's draw it blue pretend this is purple this is the
05:41occluded front you get an occlusion when the cold front catches up with the warm
05:46front essentially so that's the Norwegian model but then in the 1980s
05:50another couple of meteorologists called Shapiro and Kaiser developed a slightly
05:58different model of a slightly different area of low pressure because they looked
06:01at satellite observations they looked at numerical weather prediction so computer
06:05modeling and they realized that not all low-pressure systems form like this not
06:09all of them have an occlusion process like this so they realized that although
06:17their model starts in the same way with a warm front and a cold front like that
06:25what they realized is that in some cases the cold front wrong pen the cold front
06:40fractures like that and ends up in something called a t-bone structure a
06:46right angle situation they don't join together the next stage after that
06:51because they don't join together they don't occlude you don't get an occlusion
06:55is that the warm air wraps around the area of low pressure and the cold front
07:02continues like that why is that important well because this area of low
07:08pressure the Norwegian model has a cold core the cold air is within the low
07:14pressure center here whereas the Shapiro Kaiser model has a warmer core so that
07:23makes a difference in terms of its development particularly over the ocean
07:26and these are more common over the ocean by the way because you've got more
07:30energy more moisture as a result of that warm core and that makes it more likely
07:35to explosively deepen and looking at the satellite imagery from this let's see if
07:43we can annotate its evolution through the Atlantic and early Saturday this is
07:51when this is when it started to develop significantly jump it over to this side
08:00there's the cold front and this is a very simplified idea of what's happening
08:07and there's the warm front and you've got the warm core in the middle and as
08:13it moves you can see how quickly it deepens and eventually by the time it
08:18arrives into the UK all this warm air it's called a warm seclusion by the way
08:23wraps around like that as the cold front trailing behind and it's within that
08:31warm core this warm seclusion you've got all this energy and moisture that's what
08:35leads it to rapidly deepen as it approaches the UK and it's within this
08:39area that we saw the strongest winds we did see gales across western parts of
08:43the UK early in the day as the band of rain moved through the main band of rain
08:48then there was a lull in the winds as the area the center part of the low
08:54pressure starts to approach but it's within this core where we saw the very
08:58strongest winds and by Sunday evening it was about 8 o'clock I'm just zooming
09:08into the UK it was at this point that Tyree recorded a wind gust of 78 miles
09:18an hour you can see there's the center of the low pressure near Stornoway and
09:24you can see this way the very strong winds heavy rain pushing into Tyree now
09:30Tyree's gust of 78 miles an hour on Sunday at 8 p.m. was the strongest wind
09:36gust at that site since February 2016 that was Storm Henry and it was the
09:41strongest October gust at Tyree since 1972 so it wasn't unusually strong
09:48windstorm for Western Scotland even for Western Scotland where you get these
09:51storms in the autumn and winter it was particularly notable it wasn't just
09:56Tyree Killowin had a wind gust at the same time of 81 miles an hour and
10:03Abderran earlier in the day had a wind gust of 82 miles an hour so that's North
10:07Wales as Killowin in Northern Ireland so yeah a particularly notable area of low
10:12pressure I just thought I'd talk through that because it was I found it
10:17interesting anyway I hope it made sense to you now let's take a look at the
10:21weather over the next few days first of all I mentioned the fog overnights
10:25across East Anglia in the southeast that's the first thing that is of notice
10:31or the first notable thing in the forecaster in the next few days and what
10:36you're seeing here is there's a pressure diagram on the left there's the weather
10:39the cloud and rain and fog on the second from the left and then there's the wind
10:46and there's the temperature so by dawn on Wednesday what we've got is higher
10:52pressure just to the southeast of the UK isobars well spaced a few showers
10:57across the far south of the UK but otherwise quite extensive low cloud and
11:02fog forming mostly fog across East Anglia to the northern home counties
11:06London perhaps very poor visibility first thing so if you're traveling first
11:11thing on Wednesday then do take care on the roads fog is unlikely to be an issue
11:18across Scotland Northern Ireland Northern and Western England because
11:21there's more of a breeze as you can see on this graphic bit more of a breeze
11:25there for the north and the west of the UK so it's the southeast corner of the
11:28UK that's where the lowest temperatures will be as well so we're talking about
11:328 to 10 Celsius in main urban areas but 5 6 7 Celsius in more sheltered parts
11:38perhaps a little lower in some of the most sheltered parts of the UK but fast
11:42forward into Wednesday afternoon the fog will clear likely around about 10Z or 11
11:53local so 10Z 10 ZULU ZULU is is UTC equivalent so the way that it's a quite
12:03nice trick actually this the way to figure out fog clearance is if you
12:09haven't got access to anything else is to take the month of the year or how
12:13many months you are from say December and subtract it from midday UTC so we're
12:19two months from December so that's 10 UTC and that just is basically a rule
12:25of thumb that takes into account the fact that the Sun is getting weaker and
12:28weaker as you head towards December so take December in December would be
12:32midday UTC in November it would be 11 UTC this time of year 10 UTC the
12:39computer models agree with this other meteorological techniques agree with
12:42this for tomorrow morning's fog most likely to be 10 UTC which is 11 local
12:49time of course the clocks fall back this weekend so it would be a different time
12:54if it was this time next week it would be 10 local but at the moment it's 11
12:58local time anyway it's clearing at 11 a.m. and then it's sunny spells for much
13:04of England Wales it turns increasingly cloudy for Scotland and Northern Ireland
13:10there's a few showers around but it turns increasingly cloudy for Scotland
13:12and Northern Ireland increasingly breezy as well and then things happen really
13:18slowly through Wednesday night into Thursday as well as Friday there's an
13:23there's a cold front approaching from the West that's thickening up the cloud
13:28and by early hours of Thursday that's bringing outbreaks of rain into the far
13:32northwest of Scotland because see how slowly it's moving it's really taking
13:37its time meanwhile Thursday morning unlikely to be as foggy in the
13:42southeast because as you can see from this graphic there's more of a breeze
13:45isobars are tightening up ahead of the front as it pushes into the West
13:50meanwhile the front develops an area of low pressure so you've got similar to
13:56the basic diagram I drew earlier you've got a warm front cold front wave
14:00situation that then starts forming a circulation so that's happening to the
14:05west of the UK band of rain very slowly moving in for the start of Thursday but
14:09for most Thursday starts off dry less fog around best of the sunshine in the
14:14east of the UK breezier in the West then it turns cloudy by the end of the
14:20day across all parts but by the time you get to Wednesday Thursday evening you
14:24can see Western Scotland Northern Ireland parts of Pembrokeshire Cornwall
14:28for example seeing outbreaks of rain move in but it's taken all day to get
14:31there and there's some uncertainty which I'll go into in a moment about how much
14:35that will move in through the course of Thursday and overnight into Friday
14:39morning either way it's a mild day we've got southerly winds and it's
14:44actually mildest towards the southwest now we can show that by a nice new
14:51graphic that I developed see what you think about this this shows 2 p.m.
14:57Tuesday Wednesday Thursday Friday and it shows the temperature at 2 p.m. the
15:03highest temperature and the lowest temperature across the UK so for example
15:08Torquay hotspots at 2 p.m. today we'll see if that is the case by looking at
15:13observations later 17 Celsius whereas Orkney 8 Celsius and then by Thursday
15:19you can see it's Biddeford in the southwest that's 16 Celsius whilst it's
15:25actually Northeast England where we've got 11 Celsius and that's interesting
15:31because actually that's likely to be a sunnier place but at the same time they
15:35probably started colder because of those clearer skies overnight whereas
15:39Biddeford it's got those strengthening southwesterly winds so importing milder
15:44air ahead of the front then by Friday it's all changed again the the warmest
15:48place is in the southeast 15 Celsius coldest place at 2 p.m. by the way this
15:53is at 2 p.m. not the maximum for the day as Glennan in Northern Ireland so 9
15:59Celsius there and I'll explain some of that in just a moment but let's take a
16:04look at why that band of rain is so slow moving and to explain why we have
16:11to look at developments on the other side of the Atlantic and let's play this
16:17sequence forwards what we've got at the moment is an area of low pressure down
16:21here called Tropical Storm Oscar it was Hurricane Oscar very briefly it's
16:29reached hurricane status near the tip of Cuba the eastern tip of Cuba and it
16:36was the smallest hurricane on record with a hurricane force wind field of
16:41five or six miles so Oscar notable for being the smallest hurricane on record
16:47it's now moving north as a tropical storm didn't last as a category one
16:51hurricane for long of course being so small it's now moving north as a
16:55tropical storm it's going to weaken considerably but what it does do and
17:00this low up here also does is it causes some uncertainty in terms of the shape
17:06of the jet stream later this week and that's because what we're seeing from
17:11this area of low pressure is a warm front a plume of warmth being pushed
17:16north into Greenland and then Oscar joins in of course Oscar being an ex
17:21hurricane being a tropical storm also contains a lot of moisture and warmth
17:26that then moves north and so we've got these two pulses of warm air moving
17:30north on the other side of the Atlantic what does that do it pushes the jet
17:35stream north and that has downstream consequences on how far south the jet
17:41stream ends up diving out to the west of the UK so like cracking a whip you
17:47induce a ripple on one side of the Atlantic and that then has an impact on
17:52the other side of the jet stream the jet stream pushes north over Greenland dive
17:57south to the west of the UK but this is a small tropical storm and another area
18:03of low pressure that are both interacting with the jet stream in
18:06slightly uncertain ways over the next couple of days that then has
18:09consequences on the shape of the jet stream so naturally by Friday there are
18:13uncertainties about how amplified that jet stream is how loopy it is how
18:18regularly across the Atlantic and how far it extends south if the jet stream
18:24is particularly amplified because you get a lot of warmth pushing it north
18:28over Greenland and that then ends up forcing it even further south west of
18:33the UK if it's particularly amplified then the whole band of rain this frontal
18:40system becomes even slower moving you get more rain over Northern Ireland and
18:44Western Scotland during Thursday and into Friday and you get potentially a
18:51deeper area of low pressure forming close to the UK but if it's not as
18:56amplified then the system moves through slightly quicker you get less rain in
19:01the west less deep of an area of low pressure and so on so there are some
19:05important consequences as a result of the interaction between tropical
19:09storm Oscar and the area of low pressure moving into the Davis Strait over the
19:14next couple days that we'll be monitoring closely that also has
19:19ramifications on the weather coming into the weekend because how amplified the
19:24jet stream is on Friday will continue to impact the weather across the UK during
19:30Saturday and Sunday more on that in just a moment but let's just take a look at
19:37what the different computer model simulations are suggesting for the area
19:42of low pressure that could develop on the frontal system as it moves into the
19:46UK during Friday appreciate it would be difficult to see this clearly so I'm
19:52doing Alex Deacon and draw the UK on for you you watch the deep dive last week he
19:58did the same thing let's see if I can draw an even better area of the UK here
20:04I doubt it my drawing skills are very poor particularly I've chosen the wrong
20:12color anyway yellow so it's not at all clear but yeah that's basically the UK
20:20let's switch pens blue and each dot here is from a different computer simulation
20:26for the area of low pressure that's likely to form on Thursday night and
20:29into the start of Friday now there's a cluster just off Pembrokeshire so that's
20:34the most likely area for the low pressure system to form but there's
20:36another cluster across parts of southern Scotland for example so there's some
20:41uncertainty about an area of low pressure that's forming on a weather
20:45front as it moves in from the west during Thursday and the location of that
20:51low and its depth will have important consequences on how fast the rain moves
20:57through and how much rain we get most importantly across parts of Northern
21:02Ireland and Western Scotland this is from one computer model run this shows
21:06the 24-hour rain totals across the UK Tuesday Wednesday Thursday Friday and
21:12it picks out Northern Ireland there as and Western Scotland as the place most
21:18likely to get large rainfall totals later Thursday and into Friday but just
21:24to give you a probabilistic viewpoint this takes the output from all the
21:30different computer model runs and highlights the probability during that
21:34period to use a more appropriate pen there's the UK Wales Scotland
21:44Ireland and as you can see it picks out Western Scotland and Northern Ireland as
21:51those places most likely to get more than 50 millimeters of rain through
21:55Thursday and Friday so to summarize all of that Oscar and another low likely to
22:03cause the jet stream to become more wriggly more loopy over the Atlantic
22:06that then slows down a weather front as it moves into western parts of the UK
22:11during Thursday and into Friday if it slows down enough then not only will we
22:16see a lot of rain across Western Scotland and Northern Ireland 50 mils or
22:21more but we're also likely to see an area of low pressure forming most likely
22:26somewhere near Pembrokeshire which will again add to the rain across western
22:31parts of the UK not much rain further east but add to the rain in western
22:34parts of the UK and we're likely to see some stronger winds developing across
22:40southwestern parts of the country and just to give you an idea of that this is
22:49Friday well let's take you to the end of Thursday first of all we've got the
22:53rain moving in there's the rain into western parts of the UK it is slow
22:58moving but at this stage we've got the potential for low pressure to form in
23:06this area and that is likely to slow things down even further but also as the
23:15rain moves away eventually during Friday morning clears east lingers
23:19across northern Scotland perhaps we've got some very lively showers moving into
23:24the south and west of the country perhaps some thunderstorms especially
23:28towards the southwest where there'll also be some strong winds with the
23:32potential for 50 mile per hour wind gusts this again gives you a summary of
23:38each day over the next few days Tuesday Wednesday Thursday Friday and just to
23:41pick out first of all Wednesday as the low approaches the chance of some strong
23:46winds 50 mile per hour wind gusts that's what that's showing for northwest
23:49Scotland then on Friday these the wind gusts nothing as strong as the the low
23:57pressure systems that we saw at the end of last week and through the weekend but
24:00still some notable wind gusts towards the far southwest 50 mile an hour wind
24:04gusts perhaps and that does depend on the depth and the location of the area
24:07of low pressure and also through the Irish Sea some fairly lively winds
24:11developing during Friday but it's unlikely to continue that way because
24:20what we'll see is those systems clear out of the way and then a brief gap
24:24actually heading into the weekend so a breezy and showery day on Friday another
24:36band of rain moves into Western Scotland and Northern Ireland as well as
24:40West Wales and the southwest Saturday morning a drier spell in the southeast
24:46and this by Saturday and into Sunday as another band of rain moves into the
24:54northwest is the next aspect of the forecast that is slightly uncertain
24:59because it depends it all comes back to that shape of the jet stream and in
25:03this case if the jet stream is flatter across the Atlantic which it may well be
25:09this is how it's looking on Saturday if it's flatter then you get these weather
25:16systems basically being forced west to east across the country and quite a lot
25:24of warmth being pushed in as well from west to east and a lot of rain building
25:31up across Western Scotland, Northwest England and Northern Ireland that's if
25:34the jet streams flatter if the jet streams a bit more wriggly then these
25:41weather systems move through quicker either way through the weekend we're
25:46likely to see these systems move in from the west one of the systems really it's
25:50later Saturday and into Sunday contains the remnants of tropical storm Oscar
25:57that's this system here so this is the remnants of tropical storm Oscar not at
26:02all the tropical storm of course at this stage but it's tropical origins mean
26:07that it's well not only adds to the uncertainty through the weekend in terms
26:11of timings and speeds of weather systems as they move through but also contains
26:17some additional moisture so could end up with quite a wet spell across Western
26:22and more especially northwestern parts of the UK so this weekend's likely to be
26:26very mixed in other words we're going to see weather systems move in not just
26:30one but a few from the west and those weather systems are likely to mount up
26:37the rainfall across western and northwestern parts of the country
26:40especially over hills and so that's definitely something we'll be keeping an
26:43eye on here at the Met Office and those uncertainties continue into the start of
26:47next week however what looks most likely into next week is that higher pressure
26:54towards the south of the UK will begin to build near the UK but more likely just
27:03to the west of the UK so influential certainly but not necessarily leading to
27:10completely settled sunny weather across the country for starters we're likely to
27:16see some weather fronts trapped under that area of high pressure at first so
27:19we could see quite a lot of cloud and some rain drizzles through the early
27:23part of next week and secondly and this is interesting this is showing oh by the
27:28way that that was a pressure anomaly graphic should have explained for the
27:33whole week Monday to Monday next week and this shows the pressure anomaly from
27:37the European model so how much lower or higher the pressure is compared with
27:41normal and it shows higher than normal pressure just to the southwest of
27:45Ireland but when you look at the same model and what it's showed for the
27:53previous run 24 hours earlier and the run previous to that 24 hours before
27:58that it showed higher pressure so this is the most recent model run here this
28:05is 24 hours earlier it showed higher pressure closer to the UK and this is 48
28:09hours earlier top right higher pressure quite close to the UK there's been a
28:14subtle change in the last 24 hours the higher pressure is a bit further west of
28:19the UK why does that matter it matters because of wind direction this is showing
28:24the same thing so this is the most recent model output for the temperature
28:27anomaly through next week and what it's showing is a greater chance of
28:33northwesterly or north-northwesterly winds and as a result blues over the UK
28:38so lower than normal pressure temperature through next week 24 hours
28:42before it was showing average temperatures 48 hours before it's
28:46showing average temperatures so a subtle change in the computer modeling in the
28:50last 24 hours shifting that high just a bit further west of the UK allowing
28:54perhaps some colder winds at times either way this is showing the rain
28:59anomaly through that same week Monday the 21st of October to Monday the 28th
29:03of October I know it's 28th October to the 4th of November I beg your pardon so
29:08last few days of October first few days of November rainfall anomaly and it's
29:13showing drier than average across most of the UK but particularly towards the
29:16southwest of course that's where we normally get our wetter weather it's
29:20showing average rainfall for the north of Scotland and it does seem likely
29:24looking at some other output that we'll see still some change for weather across
29:29northern Scotland through that period so drier towards the south and southwest
29:34weather fronts and showers continuing to affect parts of northern and western
29:39Scotland at times through next week in other words settled for many but not for
29:47all and then after that there are signs that that high pressure will move but
29:52this is where paths diverge some computer models shunt the high up
29:57towards Iceland and Greenland forcing the jet stream south and more unsettled
30:02weather into the south of the UK this is the first week of November other models
30:07have the high building over Europe which would end up with the westerlies for the
30:12UK and the most unsettled weather across the north and northwest so yeah still to
30:17be determined what happens after the first few days of November a lot of
30:21uncertainty by that stage but of course we'll keep rotated right here at the
30:24Met Office and that's what I've got for you this week apologies if it was a
30:28little bit confusing at times still getting to grips with the new screen
30:31drawing things not my forte but hopefully adds to the explanations
30:36anyway and if nothing else hopefully it's cheered you up to see someone like
30:40me struggling with technology and get into grips with simple things that my
30:47daughters can do with pen that's all anyway thanks for watching and we'll see
30:52you again next week bye bye