Deep Dive 05/12/2023 – Wind and rain return – Met Office weekly weather forecast UK
This is an in-depth Met Office UK Weather forecast for the next week and beyond.
Following a freezing start to winter, Atlantic-driven weather returns in full force later this week. Before that happens, however, there’ll be a transient spell of hill snow in places... Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
Following a freezing start to winter, Atlantic-driven weather returns in full force later this week. Before that happens, however, there’ll be a transient spell of hill snow in places... Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:00 Hard to believe we're only five days into meteorological winter because we've seen so much wintry weather so far a
00:06 Change is on the way. We're back to Atlantic driven weather later this week
00:11 But will there be any more snow ice and frost before the wet and windy stuff?
00:16 Returns and how wet and windy will the wet and windy stuff be I'll be covering all of that in this week's deep dive
00:23 Thank you for joining me funnily enough tomorrow marks the one-year anniversary of the deep dive
00:28 We started doing them at the start of December last year
00:32 We've had lots of great feedback on this new format lots of new subscribers lots of likes and loads of comments
00:39 We've tried to build some topics into the deep dive based on your feedback
00:43 So keep that feedback coming and if you've not subscribed, please do so you don't miss these in the future
00:49 Now before we talk about the return to milder wetter and windier weather
00:55 Let's take a moment to marvel at some of the beautiful wintry scenes
00:59 we've seen so far this December such as this frosty scene in Shropshire over the weekend and
01:05 Indeed some snowfall. This was Lincolnshire at the weekend as well
01:11 this was on Sunday when a system moved in and brought some snow to eastern and northern parts of England and
01:17 Not forgetting the southwest because we don't get much snow in the southwest so we've got to make the most of it
01:24 I found a hill in Devon where I took my dog first time
01:29 Murphy has seen some snow a centimeter or so lying on a hill in Devon a rare opportunity to take a picture of
01:37 We should have called her snowy. That's what we were saying. We should have called her snowy
01:41 She looks like Tintin's dog and there she is in the snow and she's the dog of a weatherman
01:45 So yeah missed an opportunity there, but she's called Murphy
01:49 But of course we didn't see nearly as much snow in Devon as we saw in Cumbria
01:54 This is how it looked in Grasmere in Cumbria on Saturday or might have been early Sunday
02:01 But yeah a huge amount of snow fell there and a great example of crowdsourcing weather observations
02:09 this was weather quest a private weather company that crowdsourced the
02:13 snow depths across parts of Cumbria, Northwest England and
02:19 If you can see the finer details there, but essentially this area
02:22 saw snow depths according to public reports and also mix that with radar imagery of
02:29 25 30 and in some places 35 centimeters on the ground that accumulated through Saturday
02:35 Because of a stream of heavy snow showers that moved through during the day
02:40 Let's take a look at what that looked like from the radar imagery
02:44 Really interesting actually because I was just saying to a colleague that
02:48 It was essentially an area of showers that we saw. Let's pause it there
02:53 This is the start of Saturday an area of showers that affect to Western areas now if this was rain
02:58 Which it typically is in the UK we'd have seen what 20 to 30
03:03 Millimeters of rain falling out of these showers on Saturday
03:06 No big deal for somewhere like Cumbria to get 30 millimeters of rain
03:10 But because all that fell from as snow you multiply the depth of rain
03:16 To get the depth of snow by a factor of 10 typically it varies depending on its wet or dry snow
03:23 But we saw 30 centimeters of snow rather than 30 millimeters of snow because the air was cold enough and look at that
03:31 that's
03:32 start of Saturday this
03:34 showery stuff that was moving in also not forgetting parts of North Wales Western Scotland as well seeing those snow showers and
03:41 We saw look at that stream of showers moving in through the day on Saturday moves very quickly actually
03:47 Let's rewind it a little bit there and really it was over a 24 hour period or so. We just got
03:52 Continuous showers moving in obviously pecked up as those showers moved over the hills of Cumbria the Lake District seeing
03:59 really quite extraordinary amounts of snow a foot or so and of course that led to some significant disruption and
04:06 It was a very localized event if we rewind the clock there
04:11 Saturday afternoon many parts of the UK dry crisp cold bright
04:16 But yeah, these showers moving in the blue. We haven't got a key on this actually
04:21 I just noticed the blue is rain the white is snow you might already have guessed that many places stay dry
04:26 It was the east that saw the showers
04:29 Previous to that look at that. That's rewinding it back to Friday quite a few showers into the east
04:34 But by Saturday what we saw was a return to more of a westerly influence
04:40 But still the cold air in place and so we saw the showers more focused towards the west now speaking of that westerly
04:45 Influence if we just fast-forward it slightly and by Sunday
04:50 We saw a weather front move in this is Saturday night. Actually, there we go
04:56 Yeah, I know this because I was I was out on Saturday evening and it started raining while I was out
05:00 but we saw this rain move in mixed with the cold air and
05:04 Some quite substantial snow then developing across parts of central northern and later on Eastern England
05:12 And so I showed you that picture of Lincoln show in the snow beautiful scenes there. But yeah parts of
05:19 Northern and eastern and central England saw that snowfall
05:23 By Sunday, then another area of rain moved in now this these systems were progressively bringing milder air in with them
05:31 So the snow level all the time is rising and this system during Sunday itself was bringing snow
05:38 Over the hills of Wales, but again further east you were the more in the cold air you were and so yet for Sheffield for
05:45 Peak District for example further snowfall there through into the start of Monday
05:50 But by Monday, you can see this marked contrast across the UK
05:55 It's all wet stuff really at lower levels across England and Wales at the stage hill snow for the Pennines for North Wales
06:01 For Scotland still in the colder air
06:04 But even here rain sleet at lower levels at sea level with the snow over the hills
06:08 Likewise for Northern Ireland and then continuing that sequence through and really it was a soggy day across England and Wales on Monday
06:16 That's now pushing through its clearing. Let's pause it there go to the final frame
06:21 Whoosh, there we are lovely
06:24 That's come back
06:27 What do you behave?
06:28 Let's scroll it all the way to the final not quite the final frame. There we go. That's how it's looking midday Tuesday
06:36 turning more showery as
06:38 Most of this is rain now it clears
06:41 Eastwards, but as that low clears eastwards, let's take a look at what it does because that's quite interesting
06:48 That's the same time midday Tuesday the lows clearing east and then the blues are returning
06:57 across the UK so some colder air is
07:00 Spreading widely across the UK not as cold as it has been during the first few days of December but colder anyway
07:08 So yeah, the trend this week is for its turn milder, but the Atlantic is making a stuttering start or a stuttering return
07:16 We've seen one system bring some milder air in snow on the leading edge
07:20 Eventually turning to rain that clearing away then we're back into colder conditions for the next 24 hours
07:27 Depending on what time you're watching this, of course before
07:30 the next series of fronts move in and
07:34 This is the more definitive return to milder wetter and windier stuff. Now. Let's take a look at
07:40 What all this means because of course?
07:43 It's going to turn out to be quite a nice day on Wednesday once it's all that
07:47 Stuff moves through so this is Tuesday afternoon cloud outbreaks of rain clearing then we've got the colder air
07:54 pushing through and this is the start of
07:57 Wednesday and what you can see here is widespread blue skies
08:02 Except for where we've got some freezing fog because the winds are easing overnight
08:05 We've got the temperatures falling a widespread frost temperatures as low as -12 Celsius
08:11 possibly across some sheltered glens of Scotland for example, especially we've got some snow cover and
08:15 Freezing fog patches you can just about make them out here
08:19 So there's some through the central belt through the Grampians more especially parts of northern and central England these freezing fog patches
08:26 They could last for some time through the morning perhaps not clearing until early afternoon in places because of the light winds
08:31 The cold air in place and where that happens it will stay chilly
08:35 but further west we've got the cloud building through Wednesday and
08:40 By the afternoon, that's 2 p.m.
08:44 Wet and windy stuff pushing into Northern Ireland West Wales
08:48 Cornwall as well. Let's take a look what that means for our temperatures
08:53 So this is the maximum temperature for Wednesday and a marked contrast across the UK as the wet and windy
09:01 Weather arrives into the West. We're into double figures in Devon in Cornwall, for example
09:06 11 12 Celsius, but 2 to 4 Celsius for parts of eastern northern England parts of Scotland as well
09:13 And where we've got the freezing fog patches, of course temperatures could stay below freezing through the day and across upland parts of Scotland
09:20 Northern England temperatures could struggle to rise above freezing through the day. So that sets the scene
09:25 we've got the cold air in place across the UK except for the far west where we've got the rain arriving and
09:31 At this point it's instructive to look at freezing levels
09:36 Now we've shown these a few times on the deep dive because they're a really useful tool for determining at what height
09:42 we're likely to see some snowfall, so
09:45 This shows the height above sea level of the zero degrees isotherm
09:51 in other words as you go higher in the atmosphere the temperature gets lower normally unless there's an inversion and
09:56 At some point you get the zero degree line now where you've got very cold air
10:00 That's closer to the surface compared with where you've got the milder air
10:03 So the key here shows the grays and the blues are typically where you've got the freezing level down at 200 400 600 meters
10:11 Where you've got the greens arriving that's where it's above a thousand meters
10:15 So you're not really going to get much snow out of that at lower levels
10:18 So to determine where you're going to get snow you typically subtract around 200 meters or so it depends on the intensity of the precipitation
10:25 It depends on a number of factors the stability of the air and so on but let's just say 200 meters for now and
10:31 Then you can have a good idea of whether you're going to get snow at lower levels or whether it's going to be over hills
10:38 And what's really interesting with this actually if we play it forward and we'll go to
10:42 so we've got the cold air in place these blues and some grays over the
10:46 Scottish mountains and
10:48 actually, let's skip forward to
10:50 Start of Wednesday the greens moving into Northern Ireland that essentially means it's all rain for Northern Ireland West Wales as well as the southwest
11:00 but at the same time
11:02 We've got something known as cold air pooling across Scotland and Northern England
11:08 So this cold dense air sits close to the surface, so we've got all these grays and zooming in
11:15 to Scotland and
11:17 What you can see later Wednesday is this real contrast between the greens in the west where the snow is going to be confined to
11:24 the tops of the hills or mountains and
11:26 These grays where the snow or the freezing levels right down at the surface because of the cold air pooling
11:32 So I'm showing you this because it just illustrates how messy it gets we've got this sharp gradient between cold air and mild air
11:39 But as the mild air comes in it comes up against that cold dense air that's sitting at the surface and it mixes
11:45 but
11:47 For a time
11:48 There's the likelihood that snow will come down to the surface because at the same time as that cold dense air sitting close to the surface
11:54 We've got falling
11:56 Rainfall or snowfall and as that falls it cools the air as well. So you've got something known as
12:01 evaporative cooling so the
12:04 Precipitation falls through the air it evaporates and just like coming out of the shower the water evaporates from you you cool down
12:10 So it's cooling down the atmosphere at the same time as the mild air is rushing in
12:14 So all these factors combined make it quite a complicated situation
12:19 It's never straightforward in this country is it for determining where we're going to get snow?
12:22 and this is certainly one of those situations and
12:24 Let's just zoom it forward
12:27 And what you can see is that the milder air is pushing in but over some of these hills the cold air is persisting
12:35 So over the Pennines there, we've got the freezing level
12:38 Really covering the hills
12:40 Scotland as well, especially around the trusses towards southeastern parts of the Grampians
12:45 That's where the snow level will be probably around 350 to 400 meters during Wednesday evening
12:52 This is and it is likely to be building up over the hills at this stage with 5 to 10 centimeters
12:58 Perhaps by the end of Wednesday evening and so that could affect some of the higher routes across Scotland
13:03 Also the Pennines trans-Pennine routes as well
13:05 Not at lower levels, but some of those higher routes four times seeing a transient spell of snow the snow over the hills
13:12 three four hundred meters or so elevation but and
13:16 Again, this is at 8 p.m
13:18 Now what you can see is that milder air the green eventually mixes in and takes over fairly widely
13:24 You can see it turning all green by the start of Thursday across northern England and eventually Scotland as well
13:31 so by the start of Thursday, so this Wednesday evening that snow concern for higher parts of northern England and
13:37 Scotland and then the milder air well and truly takes over by Thursday morning and this is
13:43 Illustrated very well
13:46 by showing you the
13:48 Snow depth at 6 a.m. On Thursday and what you can see is
13:52 Yeah, 5 to 10 centimeters perhaps a smidge more over the tops of the Scottish mountains. This is the lying snow at 6 a.m
14:00 And really it's over the high parts of Wales northern England and Scotland where we've got lying snow. Not really at lower levels, but
14:08 we've also got something here that shows the change in snow depth and
14:15 The greens the green colors show you where the snow
14:19 Depth is getting lower or the snow is melting essentially and the blues and the other colors show where the snow is building up. So
14:27 On the left here. This is 6 a.m. Thursday
14:30 We've got at lower levels across Cumbria Welsh mountains parts of northern Scotland as well at lower levels
14:37 The snow is melting but it's continuing to build up over the hills
14:41 Contrast that with 6 a.m. Friday, and this is the 24-hour change in snow depth
14:46 It's virtual greens apart from the very tops of the Scottish mountains
14:51 It's virtual greens northern England Scotland and that just shows that yes
14:55 There'll be some snow building up above three four hundred meters on
14:58 Wednesday night, but by the time we get to the start of Friday
15:02 The snow is melting virtually everywhere apart from the very tops because it's so so much milder as that air moves in
15:10 Where am I going next? We've covered snow depth. I think turning milder and
15:15 Once that Atlantic weather moves in once that mild air takes over it really is here to stay now just to show you
15:25 Why this is the picture again at midday Tuesday that low moving in a brief ridge of high pressure fine day for many of us on
15:32 Wednesday, but as I mentioned
15:34 the jet stream
15:36 The low pressure the weather fronts take over and so quite a powerful jet stream actually 150 or so knots
15:43 So that's what about 160 170 miles an hour and that's roaring across the Atlantic
15:49 It's picking up these areas of low pressure and here's one. Let's just focus on this one Thursday
15:56 a bit of uncertainty at the moment on the track and depth of this low, but it's certainly got some tightly packed isobars and
16:01 those tightly packed isobars heading for
16:04 Ireland first of all and then they'll affect many southern and southwestern parts on Thursday night and into Friday
16:11 So I just want to quickly show you the wind gust graphic associated with that
16:16 because
16:18 it could be that we're looking at gales and
16:22 Quite strong gusts by the time we get to Thursday night
16:25 here's that system the colors here correspond to the wind gust values on the right and
16:30 What you can see is 50 perhaps 60 mile per hour wind gusts
16:34 Across Ireland perhaps has touched more in some exposed spots and then pushing into Cornwall. What's that by dawn on Friday?
16:42 So blustery spell winds picking up but that does depend on the exact track and depth of the low different computer models
16:48 are saying slightly different things certainly a windy period but the exact values of the gut those gusts were yet to
16:54 Finalize those details at the moment. We'll keep you updated on that and then the final thing I want to mention
17:02 Before we call this to a close is the rainfall for the rest of the week once that mild air takes over once the Atlantic
17:11 Gets a grip across the UK
17:13 It's difficult to shift those kinds of westerly patterns and the winds are going to be
17:18 in a westerly phase for some time, but certainly
17:23 with this jet stream
17:26 Starting to be well, it's returning across the UK, but it's also going to be south shifted
17:31 We saw that through much of the autumn
17:33 So southern and southwestern parts of the UK were subject to some of the higher rainfall totals during the autumn
17:40 And unfortunately that looks like the kind of setup that we're returning to for later this week. Here's the jet stream
17:47 When I say it's south shifted. There's the UK
17:51 Typically according to climatology the jet stream would be running up through the Faroes and Shetland
17:58 For example, it isn't through the rest of this week. It's hitting southern parts of the UK. So what does that mean for?
18:06 weather patterns it means that the rainfall will be focused across western and southern parts and just a
18:13 graphic to illustrate that
18:15 this here shows the
18:18 probability of more than 30 millimeters of rainfall on
18:21 Thursday so the 24 hours of Thursday once that system moves in
18:26 Dumps some snow for some of the higher parts of northern England Scotland then it turned back to rain
18:31 But this shows the probability of 30 millimeters or more of rainfall and it's picking out the strongest
18:38 Probabilities there across the Grampians so southeastern parts of Scotland there
18:43 southeastern parts of the Grampians
18:45 Southwest Scotland Cumbria
18:47 That combined with snow melt as well, of course, South Wales
18:51 Devon Cornwall, so Dartmoor for example
18:54 And then this shows the probability in the same period Thursday of more than 50 millimeters
19:00 And again, it's picking out those south facing hills across the UK
19:04 Interestingly, it's also picking out. There's a little bit of signal for some other parts that aren't south facing hills
19:11 Just over the Midlands there perhaps. Well
19:15 just over there safe for parts of Yorkshire and
19:19 There's a signal there for something that we call standing wave in
19:23 Meteorology and what that means is that as the winds come in from the southwest
19:28 they're forced to rise over the hills of say South Wales at Southwest England as
19:33 they're forced to rise then they come down over the other side of the hills and
19:38 Descend again, but they've got some buoyancy
19:41 so they descend and then they start to rise again the kind of bouncing on the other side of the hills and
19:47 On the second time that they're pushed up because they've got that buoyancy
19:53 They're not being pushed up because of the hills that's called a standing wave so they're pushed up first time over the hills
19:59 Then on the other side of the hills you've got a bit of a rain shadow
20:03 So they they start to descend again, and you've got less rainfall
20:08 then they continue with their buoyancy to rise again, and that's that standing wave and
20:13 Yeah
20:15 this
20:17 Basically is not enough time to talk about this, but it shows three different computer models
20:23 output for the rain Friday Saturday and Sunday and
20:26 To summarize it shows its wettest over Western Hills
20:30 50 to 60 millimeters over the hills of Wales Southwest Scotland for example in the Met Office model
20:36 40 to 50 there over the hills of Western Scotland and Wales in the European model
20:41 40 millimeters there for the American model and
20:44 Not nearly as much rainfall over eastern areas and so that basically
20:49 Summarizes what we're going to see through Friday Saturday and Sunday
20:52 Westerlies return bands of rain and showers move in from the west the wettest weather will be over Western Hills
20:59 There are a number of warnings in force now for rainfall for South Wales for Southwest England for Southeast Scotland
21:07 for example Eastern Scotland and
21:09 Northern Ireland as well for tomorrow night, so do check those out if you're concerned there on the Met Office website app
21:17 But that's all I've got for you this week Annie will be doing the 10-day trend tomorrow make sure you don't miss that
21:23 She'll be going into more detail about the weekend and next week, but thank you for joining me for this deep dive
21:30 Hope to see you again very soon. Bye