Convective/Storm Discussion Thread - 8th July onwards

[Mapantz]

If anybody is going chasing for this, a good starting point will be Bristol. Options galore from there, or sit tight and wait for it to come to you.

[Karl83]

20 minutes ago, Summer Sun said:

Day 2 Convective Outlook

VALID 06:00 UTC Tue 18 Jul 2017 - 05:59 UTC Wed 19 Jul 2017

ISSUED 20:29 UTC Mon 17 Jul 2017

ISSUED BY: Dan

Upper ridge over the British Isles on Tuesday will slowly drift east, as a negatively-tilted upper trough approaches from the Atlantic. On its forward side, poleward advection of a high WBPT airmass will occur from western Europe into southern then central Britain. Falling heights as upper trough approaches, combined with subtle shortwaves, will provide the focus for destabilisation of the mid-levels, with significant CAPE available from approx 850mb upwards by Tuesday evening/night.

Heavy showers / isolated thunderstorms could be possible as early as Tuesday morning close to Cornwall/Devon/Channel Islands from AcCas, though in general the risk of elevated thunderstorms here increases moreso during the afternoon hours, perhaps extending towards Dorset and Somerset by late afternoon. Bifurcating flow could also see an elevated thunderstorm complex pass close to Kent/Sussex during the first half of the evening, but more likely to stay a little to the south and hence no MDT issued for now.

Elsewhere, likely still dry at this stage, but through the evening hours increasing isentropic lift will allow numerous scattered elevated thunderstorms to develop on the leading edge of the Theta-E ridge, particularly focussed over SW England then extending east across Cen-S England, though the exact phasing of upper dynamics interacting with the plume is still uncertain - earlier destabilisation would then require the MDT to be extended farther south towards the south coast. A broken line of scattered elevated thunderstorms is then expected to drift north through the night into the Midlands, parts of Wales, and perhaps extending towards London and East Anglia - some question marks over how far east these may extend, and so have refrained from stretching the MDT too far east for now.

Some elevated thunderstorms could also form over the Republic of Ireland on Tuesday night, through a combination of advection of existing cells from SW England / SW Wales and new cells developing in-situ, generally moving towards the NW.

The magnitude of CAPE and steep mid-level lapse rates is such that lightning is likely to be very frequent with some thunderstorms, particularly those over England and Wales, and hail up to 1.5-2.0cm in diameter would be possible with the most potent cells. The risk of flash flooding is mitigated somewhat by notably dry surface layers, at least initially, but these will tend to moisten with time and bring a greater threat of some locally high rainfall totals should multiple storms move over the same area. Given the lead time, there is undoubtedly still some uncertainty over the exact forecast evolution, and further updates may be issued as new guidance becomes available.

http://www.convectiveweather.co.uk/forecast.php?date=2017-07-18

Blimey. Could Bristol finally get a pasting tomorrow night? I sure do hope so. 

Actually proper excited for a change!

[Mokidugway]

Just now, Mapantz said:

If anybody is going chasing for this, a good starting point will be Bristol. Options galore from there, or sit tight and wait for it to come to you.

Aye think I'll  use my house as chase vehicle.

[matt_in_dudley]

I'm not going to get my hopes up in all honesty, we often seem well placed and end up with just rain. I'd settle for just ONE good thunderstorm. Us Black Country folk are storm starved. I've seen 1 storm a year  i think since moving from Brownhills to Dudley almost 5 years ago and just 2 evenings worth of snow! 

On the surface things do look good though. 

 

 

[tomdewey]

There some lighting on bisc bay start to go off as I had a look on real lighting maps 

 

[weirpig]

19 minutes ago, Arnie Pie said:

 

Now now..... When were all `Greater Birmingham` we`ll be able to share all our storms

anyway a good chance for storms in our area this week....and a possible sighting of the Aurora tonight

Lol your not having our racist flag 

[AL.]

30 minutes ago, Ross Andrew Hemphill said:

Possible MCS running from the south coast to the central belt? 

Yes, straight over Swindon

[Wilxy]

Trying not to get my hopes up but its hard when you have all the forecasts going your way but at the end of the day it never goes to plan so I'll be prepared to go chasing tomorrow evening if I have to

[Another Kent clipper]

17 minutes ago, tomjwlx said:

Trying not to get my hopes up but its hard when you have all the forecasts going your way but at the end of the day it never goes to plan so I'll be prepared to go chasing tomorrow evening if I have to

It seems to be necessary on this unpredictable little island.  I remember staying over in Bristol on Saturday 29th aug 2015 witnessing what I thought was the apocalypse only to get rain and gusts.  The Midlands and the North got the lightning, precisely where I'd travelled from

[Harry]

Very interesting comparing and contrasting the various different model runs for tomorrow night. MetO graphics seeming to suggest a pulse of more active storms breaking from the general line/cluster and spreading across the SE while another moves up across more western parts (see Alex Deakin's online forecast). MetO invent however keeping the main focus across more western parts although with a clear line stretching eastwards as far as Kent, Essex and EA. GFS still looking at something a bit more widespread,along with the Arpège. WRF NMM and NetWx SR still saying west is best with areas further east staying dry(er). Interestingly NetWx MR bit more generous further East. Euro4 starts with a clear line of precip outbreaks up until 18z before fracturing with a cluster heading ENE while another moves N/NW'wards.

All a bit over the place but if I was around the Bristol/Swindon/Reading area I'd be feeling a bit more excited than I am right now (although ruling nothing out in my location to be fair)

[TJS1998Tom]

Welp, from what I can see it looks like the GFS has downgraded the precipitation and storm risk. Even though we have 24 hours I think its game over for me at least

[Wilxy]

1 minute ago, TJS1998Tom said:

Welp, from what I can see it looks like the GFS has downgraded the precipitation and storm risk. Even though we have 24 hours I think its game over for me at least

Looks the same to me nothing has changed at all which is a relieve someone correct me if I'm wrong?

[TJS1998Tom]

18z/12z comparisons with the GFS for 3am Wednesday. But of course there's still tomorrows updates yet, that said BBC weather has updated to heavy rain from light rain at around 5/6am with light rain starting at 4am

Edited July 17, 2017 by TJS1998Tom

[samadamsuk]

7 minutes ago, tomjwlx said:

Looks the same to me nothing has changed at all which is a relieve someone correct me if I'm wrong?

Bristol area looks good to me currently! The highest MU cape values decrease further west as the night progresses, which I assume is the Theta E values dropping, but still very strong nosing up in to the Bristol area.

Tough call this one! Do I stay in Cirencester, or do I get to Durdle Door for an evening swim and go from there ???? I'll get it wrong either way, guaranteed!

 Pity there is nothing surface based tomorrow eve/night - wind fields are right for some supercells it looks like, although just marginally - still, some organisation making for an interesting night anyway.

Good luck all! Samos

Edited July 17, 2017 by samadamsuk
typos galore

[AL.]

2 minutes ago, samadamsuk said:

Bristol area looks good to me currently! The highest MU cape values decrease further west as the night progresses, which I assume is the Theta E values dropping, but still very strong nosing up in to the Bristol area.

Tough call this one! Do I stay in Cirencester, or do I get to Durdle Door for an evening swim and go from there ???? I'll get it wrong either way, guaranteed!

 Pity there is nothing surface based tomorrow eve/night - wind fields are right for some supercells it looks like, although just marginally - still, some organisation making for an interesting night anyway.

Good luck all! Samos

I'm near you in Swindon, I think we should stay put.

[samadamsuk]

1 minute ago, AL. said:

I'm near you in Swindon, I think we should stay put.

Yeah I think you're probably right there - ah well, I'll have to settle for a swim in the Oasis! haha. Simulated radar seems to be following the 600mb vertical motion - may well be that I need to move slightly west to catch these, so best not be stuck on the south coast I suppose! http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=29&map=5

Samos

 

[weirpig]

Hirlam out. And as you can see from the accumulations shows the dividing line quite well  of course could be totally wrong 

Edited July 17, 2017 by weirpig

[Mapantz]

21 minutes ago, TJS1998Tom said:

18z/12z comparisons with the GFS for 3am Wednesday. But of course there's still tomorrows updates yet, that said BBC weather has updated to heavy rain from light rain at around 5/6am with light rain starting at 4am

You're looking at lower resolution charts, compared to the likes of HIRLAM/DWD/NetWx/WRF/AROME/ARPEGE - I wouldn't even bat an eyelid at the GFS precip charts now..

[samadamsuk]

Well for anyone who doesn't look to be in the firing line at the moment, don't despair! I don't think I've ever seen a setup that panned out exactly models said it would - I've driven to Kent before from Cirencester, only to find out the storms fired 100 miles west and were over Cirencester! 

 

Samos

 

[Arnie Pie]

Well i`m calling a total bust for our area.................for tonight`s Aurora showing to much cloud on SAT24 inbetween us and up north

@weirpig(and yes we know that the chains on you flag represent the chains that built the British Empire)....We`ll just put our anchor on it

and then we cor possibly be racists`s can we

 

Edited July 17, 2017 by Arnie Pie

[Nick F]

Storm & Convective Forecast

Issued 2017-07-17 22:18:34
Valid: 18/07/2017 06z to 20/07/2017 06z

DAY 1 & 2 CONVECTIVE OUTLOOK - 18TH / 19TH JULY 2017

Synopsis

A negatively-tilted long-wave upper trough extending SE from S Greenland toward Bay of Biscay will approach to W of Ireland on Wednesday. Low to mid-level flow will back S to SEly ahead of trough and will draw in a very warm / moist and increasingly unstable high theta-w plume north out of France later on Tuesday and through Wednesday, as a surface low drifts north out of W France / Biscay. Elevated thunderstorms on the northern edge / warm front of the plume are likely to develop Tuesday evening/ night and move N across England and Wales, reaching Scotland by late Wednesday morning. Hot and humid airmass in wake of these storms across England and Wales may support further storms in the afternoon

DAY 1 CONVECTIVE / STORM FORECAST – TUESDAY 18TH JULY 2017

VALID TUES 18TH 0600 TO WEDS 19TH 0600

Areas concerning … WALES, S ENGLAND, MIDLANDS, E ANGLIA …

Threats …Flash-flooding, frequent cloud-to-ground lightning, Hail

… Summary …

Isolated to scattered thunderstorms, locally strong, will bring a risk of intense downpours, frequent lightning and isolated hail to parts of southern Britain from Tuesday evening and overnight into Wednesday morning.

… Discussion …

Theta-w plume spreading north out of France Tuesday evening / night will be characterised by steep mid-level lapse rates associated with elevated mixed layer (EML) aloft originating from SW Europe. This will bolster mid-level instability in the warm conveyor spreading north from France through the overnight period, with lift of warm conveyor aided by a low-amplitude shortwave trough moving NE ahead of large scale upper trough to the west. This instability and lift supporting development of isolated to scattered elevated storms spreading north with the northern edge of the advancing plume. Scattered storms initially developing and moving north across SW England during the evening, forming clusters and then moving north through parts of Wales and the W Midlands overnight. Storms are likely to develop and drift north further east during the night across parts of central-S and SE England too – though coverage here maybe more isolated as per recent model runs.

Southeasterly low-level flow veering and strengthening to S or SWly aloft should result in 30-40 knts of effective shear … which combined with MLCAPE values of 500-1000 j/kg … will support organised clusters of thunderstorms – which may grow upscale and merge into one or two small convective complexes. Have issued a MARGINAL threat for intense/torrential downpours producing 20-30mm per/hour locally leading to flash-flooding. Frequent cloud-to-ground lightning may accompany stronger storms. Also there may be isolated incidences of large hail and strong wind gusts.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

DAY 2 CONVECTIVE / STORM FORECAST – TUESDAY 18TH JULY 2017

VALID WEDS 19TH 0600 TO THURS 20TH 0600

Areas concerning … ENGLAND, WALES, S and E SCOTLAND:

Threats …Flash-flooding, frequent cloud-to-ground lightning, large hail, gusty winds.

… Summary …

An area of scattered thunderstorms, locally strong and forming one or two storm complexes, will spread north across England and Wales Wednesday morning, before reaching S and E Scotland in the afternoon, bring a risk of intense downpours, frequent lightning and isolated hail. In the wake of these elevated storms, a very warm or hot airmass will support further development of isolated thunderstorms across England and Wales in the afternoon.

… Discussion …

… England and Wales …

Elevated thunderstorms are likely to be ongoing at breakfast time on Wednesday, spreading north across England and Wales during the morning. These storms will continue to bring a threat of flash-flooding and frequent cloud-to-ground lightning, though hail threat likely diminished.

In wake of these elevated storms drifting north, a warm and humid airmass will be in place which, with surface heating in increasing sunshine by the afternoon, will become unstable with CAPE values of 500-1000 j/kg inland widely, with E Midlands and E Anglia forecast values of 1000-1500 j/kg by GFS. Despite a lack of focus for lift to trigger storms and weak deep layer shear, surface heating and strong instability should support scattered thunderstorm development late morning onwards through to the evening, mainly N of M4/London – where SWly flow will not be modified by maritime influence so much. Strengthening SWly flow aloft may allow storms to merge and organise into linear segments – with a risk of isolated large hail, given large CAPE values, risk of intense downpours leading to flash-flooding and also strong wind gusts.

… Scotland …

Elevated storms are likely arrive and track NE across southern and eastern parts later in the morning and through the afternoon before clearing in the evening. These storms may produce intense downpours leading to flash-flooding, frequent lightning and gusty winds.

Issued by: Nick Finnis

Edited July 17, 2017 by Nick F

[Ben Sainsbury]

Typical one of the most promising risks of storms for Bristol and I'm on holiday, would post more but not had time! Good luck to you all and hope the storms can crack open the Bristol Storm Shield

[Frosty hollows]

1 hour ago, Harry said:

Very interesting comparing and contrasting the various different model runs for tomorrow night. MetO graphics seeming to suggest a pulse of more active storms breaking from the general line/cluster and spreading across the SE while another moves up across more western parts (see Alex Deakin's online forecast). MetO invent however keeping the main focus across more western parts although with a clear line stretching eastwards as far as Kent, Essex and EA. GFS still looking at something a bit more widespread,along with the Arpège. WRF NMM and NetWx SR still saying west is best with areas further east staying dry(er). Interestingly NetWx MR bit more generous further East. Euro4 starts with a clear line of precip outbreaks up until 18z before fracturing with a cluster heading ENE while another moves N/NW'wards.

All a bit over the place but if I was around the Bristol/Swindon/Reading area I'd be feeling a bit more excited than I am right now (although ruling nothing out in my location to be fair)

The mythical M4 corridor storm generator! I say mythical because I believe the M40 generates them to travel northwards! Storms here are a rarity tbh. A couple of years can go by without one. I lived in Hertforshire as a child and storms were a far more regular occurance. I also see a lot more in London/

[Ross Andrew Hemphill]

Typical for me to not be getting anything, everywhere but my part of the central belt under a warning. I know you can't take them literally but I'm always disappointed. 

[Mapantz]

I'm eagerly awaiting the 18Z NetWx SR before I head to Bedfordshire.