Storm & Convective Discussion - 20th August 2015 onwards

[cotswoldsnow]

not holding many hopes for nw oxfordshire. weve had one tiny storm all year, but a load of hail with it

[Nick F]

CONVECTIVE / STORM OUTLOOK SATURDAY 22ND AUGUST

 

Vaild: 22/08/2015 0600z to 23/08/2015 0600z

 

 

Synopsis

Upper trough tries to push east this weekend, but comes up against blocking high pressure system to the east/northeast over Scandinavia. This block causes the trough to ‘disrupt’ and become ‘negatively-tilted’, with the jet stream rounding the trough buckling and dipping south towards Spain before returning N across western UK. The flow backs to a deep southerly, with a warm, humid and increasingly unstable plume spreading N across England and Wales during Saturday. A waving frontal zone, marking western extent of the plume, will lie from SW England NEwards to NE England through much of Saturday before the front begins to pivot around a low developing over NW France and drifting N towards SW UK Saturday night.

 

 ... SW and CENTRAL S ENGLAND, E WALES, MIDLANDS, N ENGLAND and S SCOTLAND ...

 

 Plume of hot and humid air with high theta-w values and characterised by steep mid-level lapse rates will become increasingly unstable to surface heating across central and eastern parts of England Saturday afternoon, as temperatures reach as high as 29-31C. GFS indicates 500-1000 j/kg CAPE by late afternoon.

 

The plume will initially be capped around 850mb due to an EML (Elevated Mixed Layer) spreading north aloft, however, convective intiation temperatures maybe reached combined with low-level convergence of surface winds to breach the cap to allow isolated thunderstorms to develop across the Midlands and northern Home Counties during the afternoon/early evening before storms move N across parts of northern England. 

 

30-40knts of deep layer shear and moderate CAPE across Midlands and N England will be sufficient for any storms to organise into multicell line segments or even one or two supercells, capable of producing torrential rainfall leading to flash-flooding, large hail up to 2-3cm in diameter, damaging wind gusts and frequent cloud-to-ground lightning. Storm-relative helicity charts and hodographs on forecast soundings across central and N England indicate a risk of any rotating mesocyclones forming in supercellular stoms producing a tornado or two should storm bases become low enough. Forecast LCLs (Lifted Condensation Levels) suggest this maybe achievable. So have issues a Moderate risk for severe weather.

 

Further south, wind shear will be weaker, so storms will be less likely to be able to sustain themselves, though any cells towards SE England may still produce intense downpours, hail and frequent cloud-to-ground lightning. So SLIGHT risk covers this area.

Further more widespread destabilisation will take place from the S and SW overnight into Sunday morning, as a shortwave upper trough moves up from the SW creating PVA and ascent of air ahead of it, with storms spreading or developing N across the western English Channel to affect Channel Island, SW and C S England E Wales and The Midlands ahead of a surface low moving N out of France. These storms will likely be elevated, though capable of producing hail, gusty winds and localised flooding. A marginal risk area covers this.

 

... IRELAND ... 

 

West of the frontal zone in the cooler Atlantic airmass, cooling mid-level temperatures combined with sufficient low-level moisture and surface heating will support scattered showers and perhaps a few thunderstorms capable of producing hail and gusty winds.

Edited August 21, 2015 by Nick F

[r_dancing]

Wow... Manchester is slap bang in the middle of the moderate risk zone - by far one of the best places to see something tomorrow! Must... not... get... too... excited!

You're just down the road from me. I'm in New Moston.

Here's hoping everyone who wants something gets lucky tomorrow!

[cheese]

I'm trying to curb my enthusiasm - but it's not often you find yourself under a moderate warning.

Fingers crossed!

[LadyEv06]

Nottinghamshire mentioned on some posts - wayhay!!!  Hoping to see something tomorrow, its been a fairly quiet year so far! Feeling pretty muggy here tonight 

[daveywoo1977]

I still think it will shift 50 miles or so east than progged

[dusk]

TBH the possibility is there for some area's, I think tornado watch is more appropriate though.

 

Really?

 

Honestly?

 

Edited for the swear editor, which edited my mild swear for something a little more w4nk.

Edited August 21, 2015 by dusk

[A.J]

sad to say, but I bet Gordon Webb has just ordered himself some extra-strength underwear reading Nick's excellent forecast 

[lassie23]

sad to say, but I bet Gordon Webb has just ordered himself some extra-strength underwear reading Nick's excellent forecast 

Tena

[Speedway Slider]

Well J Wynn had A very different outlook for Sat afternoon, evening, night, with only small storm chance up the eastern side, Sbad wordhorpe, Grimsby, that sort of way (1am weather)

Who's correct'ish.....??

I have been trying to type the town of S C U N T H O R P E for ages!! Won't have it....

Keeps changing it to Sprunethorpe!!!!

Edited August 22, 2015 by Speedway Slider

[vladthemert]

Despite in MDT on Nicks assessment, I am thinking we probably safe from the worst, though tempting fate here, which can be always dangerous thoughts.  Not the storm worrying would love the action just worried about the rain and the damage it could bring.  

[feb1991blizzard]

Suprised such a massive area under warning, the models seem to suggest only a thin line (inluding North West) will bare brunt tomorrow afternoon, CAPE and lifted values dont seem too unbelievable tbh.

[East_England_Stormchaser91]

From current GFS/NMM/Euro 4 I would say yes. However Met Office have it more your way. I will be waiting for the morning to make a final decision. At the end of the day it will come down to radar watching, cloud spotting etc but it is helpful to be near where they are going to fire.

That tends to be the difficulty even if the models all agree. Maybe follow areas where wind convergence occurs as this may indicate a developing trough?

How about Grantham or Newark

[Supacell]

 How about Grantham or Newark

 

Who would want to bet against Lincolnshire in any thundery set up

 

But joking aside I think anywhere in a line from about Stafford to Grantham and north looks the likely place for the first wave of storms. A guess would be somewhere like Sheffield to get the clobbering but that is purely a guess.

 

Edit: The 00z NMM has just come out and that takes some storms north across from the West Midlands into NW England and the western Pennines late this afternoon before another wave develops across the likes of the Peak District and north Notts running into South Yorkshire and then northwards towards NW England. 18z Euro4 agrees with this too, so on these runs the likes of Lincolnshire stay dry. 

 

It will come down to radar watching I think. 

 

Met Office have moved the weather warning northward and expanded too to be more in line with the models. 

 

http://www.metoffice.gov.uk/public/weather/warnings

 

 

 

 

 

Edited August 22, 2015 by Supacell

[Darren Bown]

Oh dear how ridiculous

It does get a warning technically, but no more than any other storm risk day really.

[The PIT]

Take your pick make your choice. Latest nmm for us dull but temps programmed far too high unless we get some sun. Local met forecast Sunny spells cooler than NMM or netweather extra light showers later. Netweather dull morning 50% of a storm in the afternoon heavy evening rain temps too high. Met office warning isolated storms so every base is covered. Ahhh watching latest forecast everything further west and north so we are in the isolated storm area so may get some hot sun later on and a slight risk of a storm in the evening.

If we miss the storm I can get the garden done tomorrow it may have dried out.

[P-M]

I love a good thunderstorm and this year again has been great for my neck of the woods - I have seen some of the largest hail I have ever seen this year which even dented that car a bit.

 

But saying that a risk zone is just that.  You may get a storm or you may not but either way even if you don't there's some really interesting weather about.

 

I would say radar watching and checking other posters comments to see what weather they have locally and you can work out which direction any storms are headed.  This way you won't be disappointed when or if the storms pass by you and you don't get one.

 

No point in being down about stuff - the weather will do what it want when it wants despite charts and the likes.

 

Happy storm hunting today peeps!

Edited August 22, 2015 by P-M

[NO LONGER POSTING]

How can a model predict an Li of -4 -5 one day with 700-800kj of Cape but the next throw out -1-2 with 300-400kj I just don't get it

[Harry]

Sad to say I'm going to be missing this one, though residing in a sweat box lol.

Cameras and vids at the ready chaps and chapettes - could be some notable weather.

Only irritating thing is that if there is some super cellular/tornadic activity it will encourage the Express to publish doom-mongering headlines.

Good luck all and remember to keep your wits - while severe stuff in this country isn't common it can nevertheless be dangerous!!

Enjoy

Edited August 22, 2015 by Harry

[Norfolk Sheep]

Although still v happy with my storms this year (best year ever since about 1995), I can't possibly get through August without any - the month is historically usually one of the best for storms in this area. However I'm more than satisfied with the idea of 2 very warm days on the trot :D 

[Harry]

If it's any consolation August has been poor for several years in my neck of the woods, whereas growing up in the 90s it was the month that seemed to guarantee big storms, particularly the powerful overnight MCSs.

[dec10snow]

Although not in a particularly at risk area, we've been predicted to be cloudy until 10 ish this morning, however some milky sunshine has been poking through the clouds this morning, which bodes well I guess!

[Flash bang flash bang etc]

Although still v happy with my storms this year (best year ever since about 1995)...

Dude I think u need to update your sig - it says you've only had one storm in 2015 - how can that possibly make it a good storm year?!

(Unless it was the most amazing storm ever...)

[IanR]

 storms will develop over the east midlands this afternoon and move up the spine of the country towards south/west yorkshire,  seems we 'might' just scrape one here later this afternoon or early evening if lucky     , but think heavy overnight rain will be more of a feature here

Edited August 22, 2015 by IanR

[Flash bang flash bang etc]

I think it's all to play for with a large swathe of the country under at least a moderate chance of something. Nothing on the radar yet except the frontal rain in the west but that looks to be clearing, somewhat slowly. 2pm sounds like the moment it all kicks off but I'm not able to chase otherwise I'd probably head north west over the M4 to the Warwick / Northampton area and lie in wait for something.

I think personally the best chances for my area will be late afternoon, overnight tonight, Sunday during mid-morning and looking good in the east for Monday too.

One thing is for certain, there will be lightning over the UK, somewhere - and it's going to get very, very wet in many places - so if you are driving / chasing - keep slow, and remember your braking distance!

Keep safe :-)