Convective/Storm Discussion Thread - 1st June onwards

[Flash bang flash bang etc]

We might get bona fide thunderstorms if CW has it right

[Summer Sun]

Storm Forecast
Valid: Sun 01 Jul 2018 06:00 to Mon 02 Jul 2018 06:00 UTC
Issued: Sat 30 Jun 2018 08:56
Forecaster: TUSCHY

... W-France and SW-UK ...

A strong ridge is centered over SE/E France with slight weakening during the night. The general mid/upper flow turns more cyclonic betimes as the vortex over the Bay of Biscay drifts east. The low sends a marine air mass ashore over W/NW France which offsets meager mid-level lapse rates and results in 1-1.5 kJ/kg MLCAPE.

During the forenoon, a plume of elevated MUCAPE covers all of W-France and SW-UK with ongoing non-severe convection from the previous night. Graupel and wind gusts remain the main hazard. This activity, while spreading north, becomes partially surface based with an attendant increase of the gust potential (SW-UK and N-France due to a well mixed BL) and large hail (N-France only with 10-15 m/s DLS and a dry/deep subcloud layer).

Would not be surprised to see a few instances of dry thunderstorms over S-UK with thin and high based CAPE profiles in the graupel layer and a dry and deeply mixed subcloud layer. Erratic wind gusts and lightning would worsen any ongoing and potentially resulting fire risk.

For SW / CNTRL France this energy remains capped during the day although we don't want to rule out spotty mountainous convection. In case an updraft manages to survive entrainment, 10-15 m/s DLS would favor temporarily orgnized thunderstorms with isolated large hail.

Thunderstorm probabilities increase substantially over SW/W France beyond sunset, as an mid-level wave approaches from the SW. Accompanying stronger mid-level flow brings DLS in the 15-20 m/s range with MUCAPE in excess of 1000 J/kg. Elevated nature should limit the severe risk to large hail during initiation with more of an heavy rainfall threat as convection grows upscale into a large overnight cluster over W/NW France. We expanded the lightning areas towards CNTRL France as this system pushes an outflow boundary to the east. Interaction with the orography could help to spark a few thunderstorms with a low end hail and wind gust threat.

The level 1 areas cover the region with augmented severe (especially large hail). Outside the level 1 but inside the high probabilitity lightning area, isolated hail and wind gust events are also possible, but too isolated for an upgrade.

http://www.estofex.org/cgi-bin/polygon/showforecast.cgi?text=yes&fcstfile=2018070206_201806300856_1_stormforecast.xml

[Summer Sun]

Yellow Thunderstorm warning issued

Between 06:00 Sun 1st and 22:00 Sun 1st

While many areas will see little rain, thunderstorms may develop bringing torrential rain, hail and lightning to a few places.

What to expect

• Spray and sudden flooding could lead to difficult driving conditions and some road closures
• There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds
• There is a small chance of fast flowing or deep floodwater causing danger to life
• There is a small chance that some communities become cut off by flooded roads
• Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services
• There is a slight chance that power cuts could occur and other services to some homes and businesses could be lost

Further details

Heavy showers and thunderstorms may affect parts of South West England during Sunday morning, becoming more widespread and also spreading into South Wales by the afternoon. 30 to 40 mm of rain in an hour is possible, though the scattered nature of the showers means it is not certain where these higher totals and any impacts may occur. However where surface water flooding or lightning impacts do occur they are likely to be in only a few places rather than across the whole warning area. The greatest chance of impacts is in the afternoon, with the risk decreasing again on Sunday evening.

https://www.metoffice.gov.uk/public/weather/warnings#?date=2018-07-01

[Supacell]

3 hours ago, Alderc said:

Given the dryness of the ground and that precipitation totals don’t look particularly high I just wonder whether there is heightened wildfire danger from any lightning that does occur, all the ingredients are in place. 

It would appear that Estofex have seen the concerns of a fire risk too. Dry thunderstorms with the ground as it is would be quite a scary prospect, we need wet thunderstorms.

"Would not be surprised to see a few instances of dry thunderstorms over S-UK with thin and high based CAPE profiles in the graupel layer and a dry and deeply mixed subcloud layer. Erratic wind gusts and lightning would worsen any ongoing and potentially resulting fire risk."

http://www.estofex.org/

[Wiltshire_snow_lover]

The Met Office has issued its first ever thunderstorm warning with torrential rain, hail and lightning possible. The yellow 'be aware' warning is for South West England and South Wales and will be in effect from 6am to 10pm on Sunday.

https://news.sky.com/story/first-ever-thunderstorm-warning-for-uk-amid-heatwave-11421758

 

[Evening thunder]

I said a few weeks ago that there would be thunderstorms in the SW tomorrow as I'm going to be in Reading.

And right on cue... 

[Singularity]

You know what, I've been flicking through the various models for tomorrow and I can't remember seeing such a wide spread at 1 day's range before when it comes to the eastern extent of the 'potential convective initialisation area'.

Generally, the lower the resolution, the more activity kicks off and the further east this reaches. At one extreme you have GFS and NetWx-MR with intense cells over CS England by midday (in fact, mid-morning from the latter, which seems a bit crazy!) that then move toward the Bristol area while others develop over Cornwall & Devon. At the other, you have NetWx-SR which shows only very isolated cells for CS England but quite a bit of activity kicking off over Devon & Cornwall by the evening. HIRLAM is similar.

The professional outlooks mainly favour the highest resolution models, and this makes a lot of sense in convective situations. 

 

The notion of 'dry thunderstorms' put forward by Estofex sure is concerning given the tinder-dry yet well-grown (due to wet March-April) vegetation state in these parts. I have seen these on a few rare occasions in the past; often you can see a rain shaft as they approach but with it tailing off before the surface, and during the storm you can indeed see bursts of hail or graupel, usually well spaced out but larger than the typical size. At least then they melt they provide a little water (but not much per unit volume of ice due to its lower density).

[Guest]

Another thing that could be interesting is for the possibility of heat bursts with these storms, any rapidly decaying cells could lead to highly unusual spikes in temperature.

[ThundersnowDays]

Still warming up to 27.C now. 

[MP-R]

2 hours ago, Evening thunder said:

I said a few weeks ago that there would be thunderstorms in the SW tomorrow as I'm going to be in Reading.

And right on cue... 

I'll be in London too so guaranteed Bristol will get some lol.

[Tom dewey likes thunder]

 it is a shame that Wiltshire is not in the yellow warning in the south west weather warning

[philglossop]

Definitely more milky skies here in Torpoint, given I was in Exeter at Ikea (don’t ask) most of the day. But it’s much more humid here compared to previous days  

[Tom dewey likes thunder]

 good luck to Devon and Cornwall and and Plymouth and Bath and North East Somerset and Dorset and the Isles of Scilly and Torbay and East Somerset that are in a weather warning for thunderstorms and I'm disappointed that Wiltshire is not in it

[A.J]

Just now, Tom dewey likes thunder said:

 good luck to Devon and Cornwall and and Plymouth and Bath and North East Somerset and Dorset and the Isles of Scilly and Torbay and East Somerset that are in a weather warning for thunderstorms and I'm disappointed that Wiltshire is not in it

never say never Tom, we're in with a shout tomorrow 

[Guest]

7 minutes ago, ajpoolshark said:

never say never Tom, we're in with a shout tomorrow 

Quite a few of the models break out cells to east of the Meto warning zone, wouldn't be surprised to see something as far east as Portsmouth.

[Wilxy]

Just like when back in May there we no warnings in the southeast yet London was a hotspot when originally storms were forecast further west so warnings are irrelevant in these scenarios.

[Another Kent clipper]

8 hours ago, philglossop said:

Now not that I’m expecting much today ( tomorrow looks more likely) but I’ve got that ‘sick’ feeling which I get when we get storms. 

 

Plus us it feels different out there today, just more humid 

That's the feeling of a bust lol!

[Mapantz]

I'm just outside of the warning zone, but I think  it will be a very scattered affair anyway. I hope it stays dry here, as i'm close to some new records for lack of rain and consecutive dry days.

[stevofunnelcl]

something is brewing down in bay of biscay, western france could be in for quite a light show tonight, if they move north

t'will be an uncomfortable night for sleeping for sure

[philglossop]

Wish I could show this sky...

 

Looking very different here. #Torpoint 

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Sun 01 Jul 2018 - 05:59 UTC Mon 02 Jul 2018

ISSUED 19:17 UTC Sat 30 Jun 2018

ISSUED BY: Dan

Upper low will continue to be centred near NW Iberia, with a couple of shortwave impulses emanating from N Iberia and W France drifting N then NW on its eastern flank towards S / SW England. The first shortwave will be responsible for aiding the development of scattered elevated thunderstorms over Devon/Cornwall/Scilly first thing on Sunday morning, as it engages with a plume of high ThetaW advecting from France into southern Britain. This activity will tend to clear northwestwards across the Celtic Sea, though may be followed by renewed pulses of elevated showers/thunderstorms over similar areas.

 

Farther east, a complicated picture evolves as the moisture / instability plume nudges northeastwards, with potential for both elevated and surface-based thunderstorms over parts of Cen S England and the West Country during the afternoon. Dewpoints of 17-20C will be possible across the area, yielding up to 1,000 J/kg CAPE with PWAT values of 35-40mm. However, there is considerable uncertainty amongst NWP guidance due to the differences in handling of the shape / orientation of the ThetaW plume, and any hangback of cloud following morning elevated convection - both of which will affect how much instability may be available.

 

Nonetheless, it seems likely that a few thunderstorms will develop over parts of Cen S England and the West Country during Sunday afternoon, drifting into the SW Midlands and S Wales - though probably with a weakening trend. Confidence in placement and coverage of any scattered thunderstorms is not high enough to warrant a MDT for now. If the higher values of instability do develop, then hail up to 1.5cm in diameter will be possible, along with frequent lightning and the threat for localised surface water flooding - especially given the current dry ground. In all cases, elevated thunderstorms initially pose a threat for exacerbating the wildfire risk given lightning occurring over tinder-dry vegetation, before any substantial rainfall makes it to the ground.

 

Further scattered elevated showers / thunderstorms may continue to develop in a rather random fashion during the evening and overnight hours over parts of Wales / West Country / Midlands / Cen S England, as subtle forcing aloft engages the remnant instability plume in place.

http://www.convectiveweather.co.uk/forecast.php?date=2018-07-01

[Singularity]

Just to help matters (!), the 12z runs have seen the high-res models reduce the convective coverage, and the lower-res models increase it slightly (mainly extending it further east across more of CS England).

Literally a wait and see day for me tomorrow! Should be interesting but I'm genuinely concerned with respect to the lightning-fire risk.

[Tom dewey likes thunder]

In Russia where the world cup be held the a lot lighting go off .

[Tom dewey likes thunder]

The thunderStroms in bay of biscay is going like pop corn and I see it have move up west France

[Mapantz]

Some showery activity showing up on the channel now;

 

Edited June 30, 2018 by Mapantz