Storms and Convective discussion - June 2023

[Jamie M]

Day 1 Convective Outlook from Dan Holley on Convective Weather

VALID 06:00 UTC Sat 10 Jun 2023 - 05:59 UTC Sun 11 Jun 2023

ISSUED 07:36 UTC Sat 10 Jun 2023

ISSUED BY: Dan

Between an upper ridge over western Europe/North Sea (surface high over Scandinavia), and a longwave upper trough to the west of Biscay, a broad southeasterly flow will continue to advect relatively high Theta-E northwestwards across the British Isles from France. Showery rain/elevated convection will likely be ongoing at 06z Saturday across the Channel Islands, western English Channel, SW England, SW Wales and parts of Ireland in the vicinity of a NW-SE orientated occlusion. The extent of cloud cover associated with this activity as it drifts slowly northeastwards (individual clusters moving northwestwards) may, to an extent, impact the potential for deep convection later in the day, especially over Ireland. Ahead of this zone of cloud and showery rain, strong heating across the Midlands, Wales and southern England with Tmax of 24-27C anticipated widely and locally 30-31C in/around London will lead to a deep and well-mixed boundary layer. Analysis of forecast soundings suggest near-surface temperatures of 26-27C or higher will generally be required to overcome low-level capping, while very dry air persists in the mid-levels due to subsidence associated with the nearby upper ridge. This casts some uncertainty over how much deep convection will be able to develop, and it is plausible convective cloud may undergo several attempts at gaining height before become sustained, delaying true initiation until later in the afternoon. Nonetheless, profiles are anticipated to moisten fairly rapidly in the mid-levels across Wales and the West Midlands towards and beyond mid-afternoon as a shortwave approaches from the south (so here earlier initiation perhaps most favoured), while at the same time a surface low is signalled to develop over the SW Midlands. A brisk southeasterly wind across central and eastern England will aid moisture pooling along a strengthening NW-SE low-level convergence zone roughly in the vicinity of the M40-M6 corridor, with near-surface dewpoints of 15-18C signalled. This, in conjunction with orographic forcing in Wales and the West Midlands, will likely provide the focus for scattered, relatively high-based thunderstorms to develop in a fairly explosive manner, especially late afternoon and into the evening hours, growing upscale into a larger cluster across N Wales and parts of NW England.

 

Forecast soundings suggest the potential for MLCAPE on the order of 1,000-1,500 J/kg generally, but perhaps locally 2,000 J/kg where higher dewpoints exist, with cloud tops potentially to 40,000ft (-60C or colder). While flow aloft will be fairly weak (~15kts at 500hPa, for example) a reasonable degree of low-level wind shear is evident with slightly backed near-surface winds. Despite limited shear, the magnitude of instability may be sufficient for the strongest cells to become better organised with potential for some transient supercell characteristics. All-in-all, the environment will likely be conducive for some very active, slow-moving thunderstorms that may train over similar areas given steering flow roughly parallel to CZ, greatly increasing the risk of significant surface water flooding (30-40mm in less than 1 hour), especially over urban areas. Hail will likely be sub-severe for the most part, but any stronger/sustained cells could potentially produce hail ≥2cm in diameter. A SVR has been introduced for the risk of flash flooding, and to a lesser extent for locally severe hail. The deep, well-mixed boundary layer/inverted-V profiles suggest the potential for rather gusty winds, 40-50mph in the strongest cells. Greater coverage of thunderstorms is anticipated across the W/NW Midlands, C/N Wales and into NW England, where associated MDT and HIGH risk areas have been introduced, while activity will be more isolated/conditional further southeast towards London. That said, similar setups in the past have sometimes produced a rogue thunderstorm to the NW of London in the mid-late evening.

 

While nocturnal cooling at the surface occurs through the evening/night, substantial CAPE will persist given the existing deep mixed layer in the low/mid-levels, and with strengthening 600-850hPa flow through the evening this will advect more rapidly northwestwards across the Irish Sea, and eventually towards SW Scotland/Northern Ireland, and later W/NW Scotland. As such, there may be an uptick in elevated thunderstorm activity over these areas during Saturday night as the shortwave over Wales at 18z continues to migrate northwestwards.

 

Elsewhere, a couple of surface-based showers/thunderstorms will be possible over north Devon, the Pennines and SW Scotland during the afternoon/evening hours, and perhaps also a few over Connacht although this risk is much more dependent on the degree of surface heating given proximity to cloud and areas of showery rain at times through the day. There is also the chance of elevated thunderstorms emanating from northern France and/or developing in-situ across the Channel Islands/Cen S and SE England along the instability axis during the overnight period as mid-level vorticity from earlier French convection arrives from the south, but confidence in much activity here is rather low at the moment and so have refrained from including this risk for now.

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[Supacell]

Not often we see a high risk from Convective Weather. I will be heading north west into the high risk zone this afternoon.

[sheikhy]

According to those graphs i just miss out today but im on the edge so i could still see some distant lightning which can be just as dramatic!!

[I remember Atlantic 252]

7 minutes ago, sheikhy said:

According to those graphs i just miss out today but im on the edge so i could still see some distant lightning which can be just as dramatic!!

Was thinking same for here, Telford/Gnosall best placed, like for snow in winter

[Thunders]

Y’all think it’s worth staying up. In Eastbourne and there is a risk for imports but confidence is low

[East_England_Stormchaser91]

Looks very much like a repeat of June and August 2020 this setup. 
Just stepped outside now, and it felt like I had stepped off a plane in Italy or Greece! Very warm from the get go. If I get the chance, I might try and head towards the midlands later and try and get some shots of what could be some epic unimpeded views of CB’s and hopefully some decent lightning. The main area I’d go for if I was to really push the distance would be Birmingham / Stoke / Chester areas. 
 

However, as it’s high risk, and CAPE looks positively nuts, this may well be justified. I’ll see. 

Edited June 10, 2023 by East_England_Stormchaser91

[ChannelThunder]

13 minutes ago, Thunders said:

Y’all think it’s worth staying up. In Eastbourne and there is a risk for imports but confidence is low

As it stands, no. There's nothing on any model that tells me we have anything more than a <1% chance down here, so I'm not even planning to charge my camera batteries!

[Eye to the sky]

37 minutes ago, Supacell said:

Not often we see a high risk from Convective Weather. I will be heading north west into the high risk zone this afternoon.

I’m camping out in the garden tonight with my 8 year old lad. So I can guarantee we will get a storm and ruin the bbq.

[Liam Burge]

2 minutes ago, Eye to the sky said:

I’m camping out in the garden tonight with my 8 year old lad. So I can guarantee we will get a storm and ruin the bbq.

Hope you have a nice time!

[Thunders]

5 minutes ago, ResonantChannelThunder said:

As it stands, no. There's nothing on any model that tells me we have anything more than a <1% chance down here, so I'm not even planning to charge my camera batteries!

Yeah, just gotta wait for the plumes

 

[Supacell]

3 minutes ago, Eye to the sky said:

I’m camping out in the garden tonight with my 8 year old lad. So I can guarantee we will get a storm and ruin the bbq.

Hopefully they'll miss you and you and the lad can enjoy a warm, balmy evening . The risk does look much lower for our homelands so you should be ok. I have friends and family at Download who are hoping the storms miss there too. 

Our chances get higher later tomorrow and Monday. 

[Peachy]

1 hour ago, sheikhy said:

According to those graphs i just miss out today but im on the edge so i could still see some distant lightning which can be just as dramatic!!

You need to do what me and Supacell do and jump in the car and chase those storms. Trust me there's nothing like it.

[Guest]

Looks like a fun day today. Stay safe if you get caught in it or are out chasing. I debated it today but I'm going to stay put and look forward to the greater risk here in the next couple of days. Hopefully a colourful radar this afternoon!

[sheikhy]

5 minutes ago, Peachy said:

You need to do what me and Supacell do and jump in the car and chase those storms. Trust me there's nothing like it.

Oooh yeeaah!!!!!!latest ukv breaks out storms to the east of me between 1 and 2pm!!im still in the game as it stands!!!!

[Gordon Webb]

1 minute ago, sheikhy said:

Oooh yeeaah!!!!!!latest ukv breaks out storms to the east of me between 1 and 2pm!!im still in the game as it stands!!!!

one run and one model so I would advise caution and temper your hopes and expectations to avoid disappointment 

[Ian Price]

North West Eryri / Snowdonia now. 26°

[East_England_Stormchaser91]

14 minutes ago, sheikhy said:

Oooh yeeaah!!!!!!latest ukv breaks out storms to the east of me between 1 and 2pm!!im still in the game as it stands!!!!

Hoping this might be the case, as they’ll likely be more discrete and make for fantastic viewing. 
I’m probably going to bet on the initiation happening around Birmingham though and maybe up towards the peaks, due to favourable Orographical lifting helping to trigger things, and then expanding towards Stoke and Cheshire, which in my opinion will be the sweet spots later on. 

[sheikhy]

12 minutes ago, Gordon Webb said:

one run and one model so I would advise caution and temper your hopes and expectations to avoid disappointment 

Yeh im not expecting anything to be fair but at least it keeps me in the game lol!!!!

[andy989]

Nice building blocks here already over the mountains 

 

[weatherobsuk]

I'll be setting up overlooking the Cheshire Plain from this side of the western Peak District once initiation begins, given the cloud bases are forecast on the SKEW-T to be at moderate heights then visibility shouldn't be too much of a issue anyway and if things move more easterly then i've got that covered. Storm-Structure rather than being stuck in torrential downpours (from a photographic perspective) is what i'm aiming for today as tomorrow looks to be a 'hit' without needing to venture too far from home.

 

Good luck all.

[Tamsin]

I know convective rain can hit and miss but why is there a small gap around Congleton?

[A Face like Thunder]

17 minutes ago, East_England_Stormchaser91 said:

Hoping this might be the case, as they’ll likely be more discrete and make for fantastic viewing. 
I’m probably going to bet on the initiation happening around Birmingham though and maybe up towards the peaks, due to favourable Orographical lifting helping to trigger things, and then expanding towards Stoke and Cheshire, which in my opinion will be the sweet spots later on. 

Yes, unusually we seem to be in the centre of things here in S Cheshire. I shall be interested to see what happens outside later on, but more interested in seeing what happens in Istanbul later this evening!

[The PIT]

7 minutes ago, Tamsin said:

I know convective rain can hit and miss but why is there a small gap around Congleton?

Looks like an issue with your storm shield revealing itself so you'll need to fix the cloaking device.

 

Wall to wall hazy sunshine here not expecting anything bar music from radios and barbies during this afternoon.

[Harry]

1 hour ago, Thunders said:

Y’all think it’s worth staying up. In Eastbourne and there is a risk for imports but confidence is low

I suspect Dan may issue a revised forecast later if he feels confidence has improved the risk of overnighters across the S/SE. CAPE remains in situ overnight and a fresh pulse is suggested to move in by the WRF-NMM, but this model doesn’t break out any rain. AROME however does break out pocket showers/downpours. I would not be remotely surprised if we do see the odd storm overnight, but I won’t be staying up 

[Scuba steve]

17 minutes ago, Tamsin said:

I know convective rain can hit and miss but why is there a small gap around Congleton?