Storms and Convective discussion - May 2024

[LeeKay/]

I see Estofex has a 'extended forecast' issued for Sunday 12th May.

---

Quote for the UK/France:

... France into UK ...

An extensive surface pressure channel, filled with an unstable and moist airmass will be the focus for scattered to widespread CI. For France, very weak shear at all levels assists in numerous growing but rather disorganized clusters. Initiating cells, which take profit of weakly capped 500-1000 J/kg MUCAPE will pose a temporal hail and wind gust threat, but heavy rain becomes the main issue betimes. Current idea is that parts of NE France could see a rainfall-driven upgrade due to better forcing.
During the overnight hours, this risk also translates to Switzerland/far N-Italy with heavy rain the main risk.

DLS increases somewhat towards UK so a bit more progressive clusters lower the overall convective rainfall risk. Repeated thunderstorms could bring heavy rain on a local scale. Isolated hail and a few funnel reports (rich LL CAPE) accompany thunderstorms. This activity weakens after sunset.

---

https://www.estofex.org/

[Azazel]

Just outside the yellow meto warning which is great news 

[Eagle Eye]

Convective Outlook️ 

Falling surface pressure and converging moisture should allow for a deep surface rooted warm Theta-E airmass to form over Scotland during Saturday afternoon. This allowing for 100+ J/KG of 3CAPE to form with a few pockets of lift helpful for thunderstorm formation. 

 

Weak saturation and strong low-level lapse-rates should favour lightning risks but given the weak deep-layer shear it'll likely be popcorn showers thst last a short time. Meaning that storms will have to take full advantage of the environment to realise their lightning risk.

 

A large warm nose at the 700s level will take a lot to overcome and is a very possible bust risk because storms won't have long to overcome it before they can't support themselves. Especially as the lift is very low past the surface convergence.

 

The strong low-level lapse-rates and near surface convection should allow for some hail formation though, perhaps up to half an inch. Especially given the weak shearing. However, that assumes a storm can get past that warm dry mid-level nose.

[Handry Outlook]

Hi everyone, this is my first post here...

A convective outlook has been issued

Day 2 forecast

Valid: Sunday 06:00 - Monday 05:59

A low-pressure system across the Northern Atlantic will move eastward into Iceland over the weekend. This will introduce southerly winds into France and the British Isles. These southerly winds will converge with the outflow of the high pressure across Scandinavia, producing multiple troughs over the weekend.

One of the disrupting, negatively-tilted upper troughs will move northward into southwest England during early Sunday, potentially bringing some non-convective showery rain locally. CAPE of 1000-1300 J/kg will not be utilised during the early morning due to a shallow capping which requires 22-23°C to break, creating a loaded gun scenario.

As temperatures are expected to reach 22-23°C during the late morning/early afternoon, heavy and thundery showers will break out across Devon, Wiltshire, and Somerset, moving northward during the first parts of the afternoon, then northeastward during the later afternoon/early evening. Frequent or very frequent lightning is possible due to the low saturated profile and sufficient amounts of CAPE. One or two supercells could develop in places.

Moderate low-level shear across parts of southwest England and south/mid Wales can enhance updraft rotation, which increases the lifespan and intensity of the thunderstorms. This can also allow temperature and moisture gradients to increase, further boosting updrafts and allowing sustained hail growth. However, weak deep-level shear may limit the potential for significant hail growth, reducing the size of hailstones. Nonetheless, hail of 1-2 cm is possible during the afternoon.

Elsewhere, weak low-level shearing could result in outflow-dominant pulse storms that collapse and create substantial cold pools; daughter cells then form nearby, and this whole process distorts the shape and location of the convergence zone (CZ), which may shift and wriggle north/east at times through the afternoon and evening, dictating where new cells develop. The greatest concern is flash flooding from slow-moving torrential downpours, which could occur in several places; indeed, some areas could locally receive accumulations exceeding 50mm.

These thunderstorms are expected to develop in an area with high PWAT (27-32 mm) and topographic lift. This could enhance instability as moist air is forced to rise over mountainous areas in Wales, then cools and condenses, releasing latent heat and further destabilizing the atmosphere. Topographic lift can also create localized areas of enhanced upward motion and convergence, especially on south-facing slopes. These areas could become focal points for thunderstorm initiation and may experience more intense and persistent thunderstorm activity compared to surrounding areas. Coupling with high PWAT, localized flooding is likely. Isolated tornadoes are also possible due to topographically lifted environments.

During the early evening, thunderstorms might merge into a longer spell of heavy rain when they move into northern England, but the remaining CAPE should be able to support embedded thunderstorms within the heavy rain as the profile is not too saturated.

Isolated thunderstorms could also develop across parts of Scotland, Ireland, and Northern Ireland, but they are generally expected to be weak and non-severe.

An update is likely during Saturday night/ Sunday morning to readjust the slight risk and the enhanced risk. A moderate risk might also be issued only if the shearing has improved.

 

Convective Outlook Issued: Enhanced risk 12/05/2024 06:00 - 13/05/2024 05:59

HANDRYOUTLOOK.WIXSITE.COM

---

A low-pressure system across the Northern Atlantic will move eastward into Iceland over the weekend. This will introduce southerly winds into France and the British Isles. These southerly winds will converge with the...

 

[Saint coolio]

 Handry Outlook as first posts go, that’s quite a duzzie.

I think mine was something like “hi, is it really going to snow tomorrow”?

[Kirkcaldy Weather]

Good Virga display a short time ago.

In depth look at upcoming thunderstorm developments

 

 

[Flash bang flash bang etc]

Where I normally watch storms between Godalming and Guildford we saw something else in the sky last night instead

[ChezWeather]

Some crazy Aurora last night in Derbyshire easily visible to the naked eye!

 

Sunday looking tasty now, Arome and UKV favouring Wales and the West for now.   

[minus10]

 Flash bang flash bang etc wow incredible...so beautiful...were you looking north when you took these?..failing having any storms i would have Aurura instead...hopefully may see activity again tonite ?

[Eagle Eye]

Sorry for the off-topic aurora conversation but the aurora storm last night was incredible. Actual storm forecast for tomorrow should be coming this evening with a lot to discuss. 

[Pat Butcher]

 minus10  In Leeds, it was north, directly overhead, and south - although my understanding is that it was an exceptional solar storm, and northward visibility only is more standard.

[It's a Philcast]

 Eagle Eye Is it visible again tonight?

[Eagle Eye]

 It's a Philcast

Should be but not as strong. 

[Frosty hollows]

 Handry Outlook Welcome to the forum and for your forecast. Interesting 24/36 hours ahead

[*Stormforce~beka*]

 Eagle Eye Even in the South?

[Eagle Eye]

 *Stormforce~beka*

Probably only on long exposure photography. 

[Josh Rubio]

Please trend further east. Missed out to the south and west of here so many times now. 

[Flash bang flash bang etc]

 minus10 thanks!

Need to make it clear the colours are what you see in the camera viewfinder (or phone screen) and in reality with the naked eye it’s just white beams of light - but still quite astonishing.

it was literally overhead, and beams in all directions . They wax and wane pretty quickly but not in a way you can see them actually move about.

I guess the clear and warm conditions last night made it a perfect opportunity, really hoping any changeable conditions stay away until at least tomorrow evening

[Handry Outlook]

Convective outlook has been updated

Valid: Tmr 06:00 - Mon 05:59

Homegrown thunderstorms will develop rapidly across southwest England, Wales and Ireland during the early afternoon, moving northward and affecting western parts of the UK.

A low-pressure system across the Northern Atlantic will move eastward into Iceland over the weekend. This will introduce southerly winds into France and the British Isles. These southerly winds will converge with the outflow of the high pressure across Scandinavia, producing multiple troughs over the weekend.

One of the disrupting upper trough will move northward into southwest England during early Sunday, potentially bringing some non-convective showery rain locally. MUCAPE of 1500-2000 J/kg will not be utilised during the early morning due to a shallow capping which requires 22-23°C to break, creating a loaded gun scenario.

As temperatures are expected to reach 22-23°C during the late morning/early afternoon, heavy and thundery showers will break out across Devon and Somerset (potentially Cotswold area aswell), moving northward during the first parts of the afternoon, then northeastward during the later afternoon/early evening. Frequent or very frequent lightning is possible due to the low saturated profile and a sufficient amount of CAPE. One or two supercells could develop in places. Latest models are suggesting cells which is exposed in slightly stronger deep-level shear could develop into a supercell, which potentially create large hail and frequent lightning, this is most likely to develop across North Devon/ NW Wales.

Moderate low-level shear across parts of southwest England and south/mid Wales can enhance updraft rotation, which increases the lifespan and intensity of the thunderstorms. This can also allow temperature and moisture gradients to increase, further boosting updrafts and allowing sustained hail growth. However, slightly weaker deep-level shear may limit the potential for significant hail growth, reducing the size of hailstones. Nonetheless, hail of 1.5-3 cm is possible during the afternoon.

Elsewhere, weak low-level shearing could result in outflow-dominant pulse storms that collapse and create substantial cold pools; daughter cells then form nearby, and this whole process distorts the shape and location of the convergence zone (CZ), which may shift and wriggle north/east at times through the afternoon and evening, dictating where new cells develop. The greatest concern is flash flooding from slow-moving torrential downpours, which could occur in several places; indeed, some areas could locally receive accumulations exceeding 50mm.

These thunderstorms are expected to develop in an area with high PWAT (>30 mm) and topographic lift. This could enhance instability as moist air is forced to rise over mountainous areas in Wales, then cools and condenses, releasing latent heat and further destabilizing the atmosphere. Topographic lift can also create localized areas of enhanced upward motion and convergence, especially on south-facing slopes. These areas could become focal points for thunderstorm initiation and may experience more intense and persistent thunderstorm activity compared to surrounding areas. Coupling with high PWAT, localized flooding is likely. Isolated tornadoes are also possible due to topographically lifted environments. A moderate risk has been issued to highlight the area with the high chance of very frequent lightning due to topographic lift.

During the early evening, thunderstorms might merge into a longer spell of heavy rain when they move into Northwest England, but the remaining CAPE and stronger deep level shear across northern England should be able to support embedded thunderstorms within the heavy rain as the profile is not too saturated. Frequent lightning is possible locally, especially across parts of northwestern England.

Isolated thunderstorms could also develop across parts of Scotland, Ireland, and Northern Ireland, bringing localised flooding in places. Some frequent lightning is possible across west of Dublin but the likelihood is too low to issue an enhanced risk.

 

Convective Outlook Updated: Moderate risk 12/05/2024 06:00 - 13/05/2024 05:59

HANDRYOUTLOOK.WIXSITE.COM

---

A low-pressure system across the Northern Atlantic will move eastward into Iceland over the weekend. This will introduce southerly winds into France and the British Isles...

 

[LIGHTNING ACTION]

I'm busy on sunday but maybe when I get home I could see some distant anvils, since I remember i saw a big anvil from a storm that was in Manchester over here

[ChezWeather]

I'm gonna head for the western edge of the peak district tomorrow and see what happens from there, won't be chasing into the mess of traffic that is the North West that's for sure

[Frosty hollows]

 *Stormforce~beka* We had a great show here and they were also seen in Gloucester. There's another thread here with some great photos and a forecast for tonight. Cloud permitting show is expected to start 11.30 and last til dawn. 

 Handry Outlook Liking the eastward correction!

[StormLoser]

Aurora: I'm glad to report we had a nice show over Reigate around 11pm onwards.  I have never seen the Aurora, and it is something I've always had on my list of to dos.  Well, I got a great home show for me yesterday, right overhead, and all quandrants, too. The northern sky was a general wash of blue-white with a visible base and I guess that might have been the main downflow up t'north. A guess.

I hope we might see it again tonight. It is still active up there.

Edited May 11 by StormLoser

[summer blizzard]

Dark cloud already here but fairly flat. Extremely humid. 

I assume we expect nothing today.

 

[Wade]

Some big storms tomorrow in parts of Scotland, my grandparents live on the Isle of Skye and forecasts predict storms to slap bang over that sort of area, now they rarely ever get thunderstorms up there but defo will be watching the radar tomorrow, even though nothing will spawn anywhere near me.