Convective Storm/Discussion thread - 16/07/16 onwards

[Homerr]

Here's the situation above in Watford at the moment... here's to hoping something is going to pop today 

[Supacell]

Some places got some thunderstorms yesterday evening and there is a thunderstorm currently rumbling away from the north Norfolk coastline. Other than that the thundery activity overnight has been very sparse. Here in Derby I was awoken by heavy rain pattering on the window but no thunder or lightning. The legacy of the overnight rain is a lot of cloud and mistiness here. It feels cooler but still rather humid.

So onto today. I am more confident today as we have Estofex on board offering a level 1 for most of England and E Wales. Full forecast here:

http://www.estofex.org/

We also have this from Dan at Convective Weather, which is in agreement with Estofex but with a little more interest in a zone around the South/East Midlands, London and Home Counties into East Anglia. Full forecast here:

http://www.convectiveweather.co.uk/

Other forecasts I have seen agree with the above. GFS showing much more surface based CAPE than what was being shown for yesterday. The eastern portion of the UK has some capping in place around the middle of the day into the early afternoon but this is pushed back to the east coast by evening. 

    

This is reflected in the precipitation charts with very little thunderstorm activity across the areas with highest CAPE at midday but some heavy outbreaks showing up across the Midlands this evening. Overnight this risk is shown to then transfer ENE. 

The NMM is similar to the GFS but keeps the areas to the southeast of a line from Bristol to the Wash mostly dry and the storm risk is more for Mid Wales through the Midlands and N England. 

My thoughts, which are a guess considering the uncertainty, are this. The highest levels of instability and the best potential for severe thunderstorms is to the SE of the risk area and so areas highlighted in Convective Weather's forecast within the SVR box. However, there is still some uncertainty relating to how much capping will be in place (cap holds stronger on the NMM) and so the risk is lower than further N and W. Mid Wales, the Midlands and N England would seem at a greater risk of seeing some thundery outbreaks later today and it is here where I would hedge my bets on there being a few thunderstorms. With around 60knts of deep layer shear, CAPE approaching 1000j/kg, a lot of moisture in the air (dewpoints in the upper teens) and ELT's of -40c it seems quite likely storms that do form could organise into multicells producing torrential rainfall, hail of 1-2cm and gusty winds. There could also be frequent lightning. Cloud amounts could prevent surface based convection which will limit severe potential but should not affect elevated storms, which still have the capability to be quite potent.

If a storm can form to the SE of this area then I expect there is the risk of a supercell. Cloud amounts could again stifle chances of this but if this was to happen then there is the threat of large hail up to 4cm in diameter (according to Estofex charts) and an attendant tornado risk as per the below charts from Lightning Wizard:

http://www.lightningwizard.com/maps/

  

A very interesting day and all to play for IMO. I cannot chase far but I am off work with my kids and so can go on a short chase if need be. I am hoping I can stay at home though and see something come to me.

 

 

[Nick F]

Bit late with my forecast, but a lot to take in and tricky to forecast the potential for severe weather, which despite favoured by parameters is dependent on forcing breaking the cap, but will give it my best shot ... 

Storm & Convective Forecast

Issued 2016-08-25 08:53:04

Valid: 25/08/2016 0600z to 26/08/2016 0600z

CONVECTIVE / STORM FORECAST - THURS 25TH-AUGUST-2016

Synopsis

Upper trough over the N Atlantic continues to slowly advance across western British Isles, ahead of it a slow-moving waving cold front lies SW-NE across England and Wales during Friday, with an unstable warm and humid airmass ahead of the front across central, southern and eastern England. There will be a continuing risk of thunderstorms along and ahead of the cold front on Thursday. Also, EIRE, N. Ireland and western Scotland will be at risk of a few storms later as upper trough and associated cold mid-levels moving in steepens lapse rates.

… E WALES and ENGLAND …

A departing shortwave or vort max bringing some elevated storms to E Anglia this morning now clearing, otherwise, forcing for ascent will initially be too weak this morning to produce much in the way of convection from the potentially unstable warm and humid conveyor continuing to advect NE across England.

However, WV imagery this morning shows a subtle shortwave trough moving NE over the Bay of Biscay, currently producing storms over the same area. This shortwave may engage cold front to develop another wave to ripple NE across England. Increased low-level convergence ahead of frontal wave and large scale ascent aloft from shortwave and approaching  large scale trough to the west will favour the re-development of elevated storms tracking NE embedded in more general heavy rainfall expected to re-develop close to or along slow-moving cold front across northern and western parts of England on Thursday. There is a risk of localised flooding produced by these storms, particularly this evening and through into the overnight period across central and eastern parts of England, when most models expand coverage of heavier rainfall as forcing increases with approach of upper trough from the west. So have included a MARGINAL risk of severe weather.

Further east across SE England and E Anglia, capping of warm and humid surface airmass will be present, good sunny spells spreading NE here this morning should allow strong surface heating by this afternoon, with CAPE values approaching 1000 j/kg indicated by models. Surface heating, low-level convergence, increasing lift aloft from approaching shortwave trough and approaching large scale upper trough to the west may produce sufficient forced ascent to break the cap this afternoon to allow a few surface-based storms to develop across eastern England.

A SLIGHT risk has been highlighted for E England for the potential of surface-based storms which will tap into a rather warm and moist surface airmass (dew points of 17-18C) and will likely quickly organise within an environment of strong deep-layer shear in the order of 40-50 knots. Supercells may develop briefly, capable of producing isolated large hail (2-3cm), torrential downpours leading to flash-flooding, strong winds and frequent cloud-to-ground lightning. Also, low-level wind convergence from sea breeze interaction with synoptic flow and outflow from convection further west near cold front may even produce an isolated tornado or two, given large CAPE and sufficiently low LCLs. However, there remains a question mark over whether there will be sufficient forcing to break the cap to produce such storms, so stuck with a SLIGHT risk.

Cold front is expected to gradually clear east from E England during first part of Friday morning, any severe surface based storms will clear into the N Sea late evening,  then more general heavy rainfall with embedded elevated storms will move in from the west overnight before clearing the east coast by dawn. There will be continued risk of isolated flash-flooding overnight from these embedded storms.

... EIRE, N. IRELAND, SCOTLAND ...

Lapse rates will steepen here later as Atlantic upper trough moves in aloft and introduces colder air aloft. So scattered heavy showers and thunderstorms will be on the increase here today. Deep layer shear and upper wind strength will be sufficient for some storms organisation, with hail and gusty winds possible, though cooler surface temperatures and modest moisture will tend to limit severe potential.

Issued by: Nick Finnis

Edited August 25, 2016 by Nick F

[Speedway Slider]

We're there any lightning strikes over west/east midlands, east anglia from that large mass of heavy rain that moved north east over the country overnight?

Not inc the storm that's exited the east coast over the last half hour or so...?

Not sure if I dreamt this storm, or it was real!!! (Leicester) between 03:30 and 08:00 this morning!

[Ben Sainsbury]

3 minutes ago, Speedway Slider said:

We're there any lightning strikes over west/east midlands, east anglia from that large mass of heavy rain that moved north east over the country overnight?

Not inc the storm that's exited the east coast over the last half hour or so...?

Not sure if I dreamt this storm, or it was real!!! (Leicester) between 03:30 and 08:00 this morning!

All lightning today so far...

 

Edited August 25, 2016 by Ben Sainsbury

[weirpig]

3 minutes ago, Speedway Slider said:

We're there any lightning strikes over west/east midlands, east anglia from that large mass of heavy rain that moved north east over the country overnight?

Not inc the storm that's exited the east coast over the last half hour or so...?

Not sure if I dreamt this storm, or it was real!!! (Leicester) between 03:30 and 08:00 this morning!

Im to the west of you   but all i had was heavy rain  no storms as such.

[Azazel]

my vibe for today and areas of interest.

 

 

[staplehurst]

9 minutes ago, Speedway Slider said:

We're there any lightning strikes over west/east midlands, east anglia from that large mass of heavy rain that moved north east over the country overnight?

Not inc the storm that's exited the east coast over the last half hour or so...?

Not sure if I dreamt this storm, or it was real!!! (Leicester) between 03:30 and 08:00 this morning!

This is 7am yesterday to 7am this morning… (lightning are the black dots)

[dave48]

4 minutes ago, staplehurst said:

This is 7am yesterday to 7am this morning… (lightning are the black dots)

In the absence of any other specific forecasts for the UK yesterday, and with estofex giving a no risk area, you played that very well, a superb forecast on a day with just about as much uncertainty as you can find.

Edited August 25, 2016 by dave48

[Speedway Slider]

9 minutes ago, weirpig said:

Im to the west of you   but all i had was heavy rain  no storms as such.

Thought it was a dream!!! But boy did it rain!!

[Ben Sainsbury]

And here is my take on today...

[Speedway Slider]

4 minutes ago, dave48 said:

In the absence of any other forecasts for the UK yesterday, and with estofex giving a no risk area, you played that very well, a superb forecast on a day with just about as much uncertainty as you can find.

Yea, great effort, i'd take that accuracy any day of the week, well done!!

[staplehurst]

5 minutes ago, dave48 said:

In the absence of any other specific forecasts for the UK yesterday, and with estofex giving a no risk area, you played that very well, a superb forecast on a day with just about as much uncertainty as you can find.

Thanks Dave - mid-level plumes and the like are always fraught with uncertainties, but this particular spell feels moreso than 'average'. Hard also trying to gauge which bits of precip could turn thundery - wasn't overly-sold on the outer frontal wave type feature (that ran over the Midlands in the early hours) being thundery, hence kept the SLGT over the narrow corridor where lightning seemed more likely from elevated thunderstorms. Coverage didn't look great enough to upgrade to MDT, hence the comment in the forecast text about it not being as active as the 19-20 July event.

Today is not really any more clear-cut. General idea being the risk of TS activity increases later today and into this evening/tonight, but as to where, how active will lightning be, will we develop a supercell with large hail? A lot of uncertainty, but the potential is there for sure!

[Summer Sun]

Met office rain warnings out from today till Sunday

Issued at:
10:30 on Thu 25 Aug 2016

Valid from:
15:00 on Thu 25 Aug 2016

Valid to:
04:00 on Fri 26 Aug 2016

Areas of rain, locally thundery, will develop across the warning area during Thursday afternoon, evening and overnight. This will be heavy at times and may lead to some localised disruption. Lightning will be an additional hazard, especially across areas south of Birmingham.

Heavy rain may lead to localised rainfall accumulations of 20-30 mm in 1-2 hours, with some places perhaps seeing 40-60 mm in 3-6 hours. This may cause some travel disruption during rush hour this evening. The threat of heavy rain will clear eastwards later in the night, clearing western parts of the warning area by around midnight.

Issued at:
10:37 on Thu 25 Aug 2016

Valid from:
15:00 on Sat 27 Aug 2016

Valid to:
09:00 on Sun 28 Aug 2016

Outbreaks of rain will develop over central UK through the course of Saturday, and by the evening are likely to be heavy at times. This rain is likely to be prolonged over many areas overnight into Sunday morning, gradually becoming lighter and dying out later on Sunday. Please be aware of the risk of local disruption to transport and outdoor activities.

A frontal zone associated with very warm and moist air over southern UK early Saturday will ease northwards during Saturday, and become slow moving over central areas of England and Wales later Saturday, persisting overnight, before slowly easing away to the east during the course of Sunday. Rainfall will be heavy at times, and locally prolonged. Rainfall totals are likely to be in the range of 20-40 mm, but 50-75 mm is possible in some areas.

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1472079600&regionName=uk

Edited August 25, 2016 by Summer Sun

[dave48]

'Areas of rain, locally thundery, will develop across the warning area during Thursday afternoon, evening and overnight. This will be heavy at times and may lead to some localised disruption. Lightning will be an additional hazard, especially across areas south of Birmingham.

Heavy rain may lead to localised rainfall accumulations of 20-30 mm in 1-2 hours, with some places perhaps seeing 40-60 mm in 3-6 hours. This may cause some travel disruption during rush hour this evening. The threat of heavy rain will clear eastwards later in the night, clearing western parts of the warning area by around midnight.'

 

Don't recall the met office giving such a specific mention for lightning frequency before.

[weirpig]

Met  seem fairly confident  of the potential storm track  which seems to put it staright through the heart of the country from now right till Sunday  

[sparky1972]

morning all, was really hoping its was going to be very stormy last night, but alas, a few flashes and very distant rumbles not much happened here, woke this morning to rain, now dry with very hazy skies, sun trying to come out, think we will need it to help aid any storms to build, temp currently 20c     have just seen the met office warnings south Lincs is just outside it, looks like north Lincs will get something

Edited August 25, 2016 by sparky1972

[weirpig]

35 minutes ago, Azazel said:

my vibe for today and areas of interest.

 

 

Actually that wasnt a bad shout  not to dissimilar to the mets update a few minutes ago   thats of course if it happens like that   i think perhaps it will be more to the east 

[Mapantz]

29 minutes ago, dave48 said:

'Areas of rain, locally thundery, will develop across the warning area during Thursday afternoon, evening and overnight. This will be heavy at times and may lead to some localised disruption. Lightning will be an additional hazard, especially across areas south of Birmingham.

Heavy rain may lead to localised rainfall accumulations of 20-30 mm in 1-2 hours, with some places perhaps seeing 40-60 mm in 3-6 hours. This may cause some travel disruption during rush hour this evening. The threat of heavy rain will clear eastwards later in the night, clearing western parts of the warning area by around midnight.'

 

Don't recall the met office giving such a specific mention for lightning frequency before.

I've seen that quite a few times..  What makes that slightly interesting, is the fact that Birmingham is in the bottom quarter of their coverage, and they're saying south of that.

[Thunderstruck]

As long as Clacton stays dry today, I don't really mind! 

[weirpig]

3 minutes ago, Mapantz said:

I've seen that quite a few times..  What makes that slightly interesting, is the fact that Birmingham is in the bottom quarter of their coverage, and they're saying south of that.

yes i noticed that  seems to be saying glos up to brum for the lightening activity.  Is there any reason why this risk isnt being highlighted further north?

[AWD]

20 hours ago, Mapantz said:

12 minutes ago, Mapantz said:

I've seen that quite a few times..  What makes that slightly interesting, is the fact that Birmingham is in the bottom quarter of their coverage, and they're saying south of that.

 

Which, if I am reading everything correctly, means lightning is most likely between Birmingham & Clevedon?

[weirpig]

4 minutes ago, AWD said:

Which, if I am reading everything correctly, means lightning is most likely between Birmingham & Clevedon?

Looks that way   we could just keep driving up and down the M5  should see something then

[MattTarrant]

Brightning up nicely here with temperatures rising steadily! A few rumbles would be nice later this afternoon!!

[AWD]

4 minutes ago, weirpig said:

Looks that way   we could just keep driving up and down the M5  should see something then

You'll probably be lucky to get down the M5 in one day, let alone back up again!