Convective / Storm Discussion Thread - 31st May 2017 onwards

[Flash bang flash bang etc]

I'm in Maidstone first thing tomorrow but will probably be outta there by 12 so no storms for me...

[TJS1998Tom]

Long way off so just for fun, but this would be interesting if it came off (18z)

[Supacell]

From looking around the various forecasting sites it looks like a chance for a few thunderstorms in the far east today - East Anglia and SE England. All the forecasts I have seen have the speed the cold front moves east as a possible spoiler as if it moves through quicker than expected then it pushes the storm risk east with it. Some forecasts show the cold front itself pepping up overnight but I am unsure how thundery any rain on the front would be by this stage as all the CAPE is pushed eastwards by the time it reaches the south-east. The exception to this is the NMM which keeps the CAPE hanging around long enough for the cold front to move into the area of CAPE this evening, this would likely yield a line of thunderstorms through the evening. It is just one model though, the GFS pushes the CAPE east and out of the UK much faster. I am unable to see the WRF as the site I use seems to be down.

If I was in East Anglia or the far SE then I would be considering the risk of a few storms this afternoon and then a very slim risk of some more later this evening. Where storms do occur they could contain lightning, maybe fairly frequent and gusty winds. Hail seems less likely, but torrential rain could occur in any storms giving a risk of flooding. Anywhere west of a line from the Wash to Brighton seems to far west today (unfortunately).

[UKSupercell]

I work just outside Guildford and it feels muggy this morning, plus the sky is looking pretty unstable. Seen some altocumulus castellanus and cumulus already building. That sky really looks promising but who knows. It was like this back in south Bucks driving down the M25 this morn. 

[Andy Bown]

There is discrete mid level convection here, approximately 100 miles ahead of the front, so that is promising for further east.

[Nick F]

Storm & Convective Forecast

Issued 2017-06-02 06:50:23

Valid: 02/06/2017 06z to 03/06/2017 06z

DAY 1 CONVECTIVE/ STORM FORECAST - 02 JUNE 2017

Synopsis

Upper longwave trough over the North Atlantic advances eastward towards the UK on Friday, a cold front lying from SE Scotland down across NW England, Wales and far SW England at breakfast time pushes slowly east today, to lie appox. Humber to Dorset by midnight tonight. A warm and humid airmass across SE UK ahead of the  cold front will become unstable this afternoon with surface heating, supporting development of a few thunderstorms.

… SE ENGLAND and EAST ANGLIA …

Warm/moist flow off the near continent across the above areas ahead of the cold front to the west will become increasingly unstable into this afternoon, as temperatures reach the high 20s centigrade in sunshine while low to mid-level lapse rates steepen as colder air arrives aloft with eastward advance of upper trough. GFS develops 300-600 j/kg CAPE this afternoon across the above areas, weak surface convergence and increasing large scale ascent as upper trough approaches from the west should be sufficient to allow a few thunderstorms to develop this afternoon during peak heating. 30-40 knot 500mb SWly flow may organise storms into a few linear clusters capable of producing localised high rainfall rates (20-30mm per/hour) which may lead to localised flooding. Directional shear will be fairly weak though, so storms will tend to produce only small hail and locally gusty winds. But have included a MARGINAL risk of severe weather for the risk of flooding/treacherous driving conditions.

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Fri 02 Jun 2017 - 05:59 UTC Sat 03 Jun 2017

ISSUED 07:26 UTC Fri 02 Jun 2017

ISSUED BY: Dan

UPDATE 07:26 UTC Latest guidance continues to trend towards a reactivation of the frontal boundary this evening/overnight with showery outbreaks of rain developing over the Midlands into East Anglia - questionable as to how much (if any) lightning activity will be present with this, but given some marginal elevated instability have extended the LOW threat westwards to cater for this potential. That aside, still some uncertainty as to how things will evolve this afternoon with regards to surface-based thunderstorm potential over East Anglia / SE England - early initiation (11-14z) is still signalled by some NWP output.

Broad upper vortex will approach from the Atlantic, preceded by a strengthening southerly flow encouraging advection of a warm, moist airmass at low-levels ahead of an eastward-moving cold front.

There is the potential for some elevated convection to develop over the English Channel and drift into SE England late Friday morning. Then, given enough insolation, combined with low-level convergence, a few scattered thunderstorms will be possible in the warm sector during the afternoon and evening hours across E/SE England. This is highly dependent on the speed of the cold front, which carries some uncertainty - in general, a quicker arrival will narrow the window of opportunity for phasing with maximum daytime heating.

Nonetheless, given 600-800 Jkg-1 CAPE and reasonable DLS a few thunderstorms seem plausible at least, in an environment favourable for organisation into multicells and perhaps even a supercell. Initiation could be as early as 11-14z. Forecast profiles look fairly saturated, so hail perhaps not such an issue - though the strongest cells could produce local incidences of hail up to 1.5cm in diameter. Surface water flooding perhaps more of a significant risk given PWAT 30-35mm - scope then for 25-30mm to fall in a short space of time.

There are also suggestions amongst NWP guidance of an additional cluster of elevated deep convection to occur during the evening and night hours over similar areas.

A few scattered heavy showers will also be possible Friday afternoon across parts of Scotland, perhaps weakly-electrified given strong shear but marginal instability - hence an eastwards extension of the LOW threat level. In the post-frontal environment, cooling aloft will steepen lapse rates and bring a few scattered showers late in the day and into the night across the Republic of Ireland, Northern Ireland and into western Scotland - some perhaps weakly electrified.

http://www.convectiveweather.co.uk/forecast.php?date=2017-06-02

[Harry]

Cloud amounts already seem to be on the increase here. This will not help too much which insolation which, aside from any trough that develops, could be a key player in assisting with the initiation of storms.

I agree with @Supacell (which probably means I've just lost the election, lol), in that NMM is opting for fairly decent CAPE actually (around 1,200 - 1,500 J/Kg) and keeping decent MUCAPE (again, in excess of 1,000 J/Kg) hanging around until around 23:00.

While it is unpopular, I consider the NMM to be one of the most reliable at very short range (not to say that it's always accurate, because clearly it is not).

Edited June 2, 2017 by Harry

[Flash bang flash bang etc]

Can confirm as I head into Kent there are good signs of instability

[Hodgheg]

Last day on the broads today so hoping for something decent. Already have signs of instability but the high level crud is also increasing. 

[Nick F]

8 minutes ago, Harry said:

Cloud amounts already seem to be on the increase here. This will not help too much which insolation which, aside from any trough that develops, could be a key player in assisting with the initiation of storms.

I agree with @Supacell (which probably means I've just lost the election, lol), in that NMM is opting for fairly decent CAPE actually (around 1,200 - 1,500 J/Kg) and keeping decent MUCAPE (again, in excess of 1,000 J/Kg) hanging around until around 23:00.

While it is unpopular, I consider the NMM to be one of the most reliable at very short range (not to say that it's always accurate, because clearly it is not).

Warm but hazy sunshine now here in south London with high thin cloud, should get hot and humid enough.

[Hodgheg]

I'm liking the look of this. 

Edited June 2, 2017 by John Hodgson

[Thunderstruck]

Very hazy skies here. It's hard to say what's happening higher up because I can't see through the haze! Nice breeze coming in through the window though.

I've got a dentist appointment at 11:30 so hopefully nothing happens until the afternoon.

[Robbie Garrett]

1 hour ago, Harry said:

Cloud amounts already seem to be on the increase here. This will not help too much which insolation which, aside from any trough that develops, could be a key player in assisting with the initiation of storms.

I agree with @Supacell (which probably means I've just lost the election, lol), in that NMM is opting for fairly decent CAPE actually (around 1,200 - 1,500 J/Kg) and keeping decent MUCAPE (again, in excess of 1,000 J/Kg) hanging around until around 23:00.

While it is unpopular, I consider the NMM to be one of the most reliable at very short range (not to say that it's always accurate, because clearly it is not).

Just flew in from Austin, TX.  19c at 3000ft and a little lumpy with tops up to 6-7000ft with bases at 5000ft+

[Snow Slave]

13 hours ago, samadamsuk said:

Hey All -

Great animation of a HPC model of the El Reno supercell & F5 nader here (posted on Stormtrack ) - http://news.wisc.edu/a-scientist-and-a-supercomputer-re-create-a-tornado/

I'm hoping for a couple more rounds of thundery weather coming up in the next week or so - models look like they're going that way. Good luck to all chasing tomorrow!

Samos

 

Wow that was cool. Thanks for sharing! 

[Justin123]

At the moment im in Harlow, essex, but at 12 off to basildon. Off to the east now there are many cumulus bubbling up, it looks as if they could develop into MCS as they are building along a line NE-SW, cant wait for some action! 

[Harry]

Sun out here, very warm and humid outside.

I can't help but think I am possibly a little too far West and South, but would be delighted to be wrong.

Edited June 2, 2017 by Harry

[Thunderstruck]

Very humid here too, but still no sign of the sun

[UKSupercell]

Sun was out here for a while with high cloud but now it's gone fairly cloudy with dark cloud bases and some visible cumulus towers. Looks somewhat promising tbh. This is near Guildford. 

[Team Jo]

Just parked up at Thorndon on the way back from shopping which looks out WSW. Hazy and humid, definitely looking a bit unstable, some cu starting to build out towards the capital. Think we are going to pop home and grab some lunch and then come back with the camera and stuff. 

[Harry]

Fairly sustained heating happening here over the past few hours. TCu beginning to appear particularly to my N and E. I wouldn't be surprised to see intiation within the next 60 - 90 minutes.

[UKSupercell]

How do I upload photos from my iPhone to this thread? If it's something to do with going to your attachments, apparently I've used 10 of 4 available MB, and there's no option to delete any existing attachments? 

[Harry]

@UKSupercell Sorry mate no idea, other than to access the forum via my phone, click choose files and select from my library.

Scratch my earlier post, looks like something could be getting its act together just to my N. ETD (estimated time of detonation), circa 30 mins is my hunch, perhaps sooner.

[Team Jo]

Something just popped up to my south over the estuary. Looks like we are go!

[tomp456]

When large swathes of your region has a chance of a storm, but you do not.