Storms and Convective discussion - May 2024

[Scott Ingham]

The latest UKV also pushes the worst of the storms further east into the midlands slowing into South Yorkshire. Again it’s a now cast but I’d suggest the more western areas will miss the worst of this now on current trends

[WeatherArc]

Some great soundings from the Arome tonight, liking shear profiles. Real potential for 2,000+ sbcape in some areas.

Soundings taken from midlands, wales and Bristol areas.

Honestly i dont mind whether i get hit or not tomorrow, just looking forward to seeing those distant towering cumulus.

[Handry Outlook]

Convective outlook FINAL UPDATE

Valid: Today 06:00 - Tmr 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.

Update (12/05/2024 05:25): Latest high-resolution models indicate the presence of increased deep-level shear, prompting the expansion of two high-risk areas as well as the moderate-risk zone. The risk of MCS has incresased across West Midlands and Northern England due to the latest upgrade of deep level shear.

Update (11/05/2024 22:00): Latest high-resolution models indicate the presence of increased deep-level shear, prompting the addition of two high-risk areas and expansion of the moderate-risk zone.

A low-pressure system across the Northern Atlantic will move northeastward 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 1700-2500 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 along the Bristol Channel surrounding area, 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 Bristol/Newport and N 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. Latest CAM models are also suggesting an upgrade in terms of deep-level shear comparing to previous runs. Therefore hail of 1.5-3 cm in diameter 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.

Thunderstorms are forecasted to form in regions with elevated PWAT levels (>30 mm) and topographic lift. This combination may intensify instability as moist air ascends over Welsh mountains as well as Exmoor, cooling and condensing, releasing latent heat and further destabilizing the atmosphere. Topographic lift can additionally generate localized zones of increased upward motion and convergence, particularly on south-facing slopes, serving as potential thunderstorm initiation points. These areas might witness more vigorous and sustained thunderstorm activity compared to their surroundings. With the coupling of high PWAT, localized flooding is probable, and isolated tornadoes could occur due to topographically induced environments. Two distinct high-risk zones have been designated to pinpoint areas with a heightened likelihood of frequent lightning, primarily due to topographic lift. Strong gusts (up to 55 mph) and isolated tornadoes are possible should any supercells develop.

During the early evening, strong thunderstorms across N Wales might merge into a MCS when they move into Northwest England, remaining CAPE and stronger deep level shear across northern England should be able to support frequent lightning thunderstorms within the potential MCS as the profile is not too saturated. Heavy and torrential downpours are expected across NW England, bringing a risk of flooding,

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

 

Convective Outlook Updated 3: High risk 12/05/2024 06:00 - 13/05/2024 05:59

HANDRYOUTLOOK.WIXSITE.COM

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Update (12/05/2024 05:25): Latest high-resolution models indicate the presence of increased deep-level shear, prompting the expansion of two high-risk areas as well as the moderate-risk zone. The risk of MCS...

 

[Cain]

 

Nice an sunny here so far 

Edited May 12 by Cain

[Rush2019]

Good instability aloft here this am, with a little updraft too, a  good sign of surface heating conducive to breaking any capping later. A good afternoon for sky and radar watching. 

[Cain]

Was quite sunny 

[Petorious]

Good morning, looking like a very interesting day for quite a few. Would love to see some of these storms push a little further east, I guess its not impossible looking at the models. Was out driving with a couple of mates looking for the Northern lights last night which was a bust, and after a day of work from 2am in the morning, I am like a zombie today which would mean no chasing tonight lol.

Lets keep fingers crossed that the area of these storms may push or grow to cover slightly more east.

Edited May 12 by Petorious

[ANYWEATHER]

The skies above  beautiful Hay on Wye , show potential …..perhaps !?

[Petorious]

Reading, Oxford, Winchester area. Something showing up there, early morning precip that will burn off or something more sinister? Also has the NNE direction.

[weatherobsuk]

Now the excitement of the Aurora storm is almost drawing to a close i'm turning my mind towards today's thunderstorm action and hoping to intercept a few cells on the Derbyshire/Staffordshire border. Manchester METAR looks promising with cloud bases initially starting at 4000ft before dropping down to a modest 750ft as the MSC from Wales moves through, but there could be some photogenic opportunities in the hours to come once things get going in mid-Wales. 

[Cain]

Some nice breaks in the cloud now hopefully sun will get to work 

[Alderc 2.0]

Not that we’ll see anything down here but lots of Ac Cas streaming north overhead. 

[Andy Bown]

 Alderc 2.0 yes it’s become very noticeable over Wiltshire in the last half hour. 

[Cain]

Sky is full of this 

[Slysi100]

An unstable looking sky if ever saw one. This taken yesterday evening down in south Devon. Feels very muggy this morning although being right by the sea I don't think I'll see any storms unfortunately. These more likely will form inland towards North Devon. We'll see though

[Eagle Eye]

Current state of play

2-5 PM initiation

Most models initiation in the SW and western Wales moving NE into the late evening.  One cluster in northern Wales into NW England on all models, weaker on AROME. Second cluster initially forms in southern Wales, strengthening into the Midlands for a time. Not on all models but on most. Expect frequent lightning from both of the storms. Deep-layer shear stronger for the NW one, quicker upscaling and potentially lasting longer.  AROME combines two clusters over Midlands and NW and this is where they're strongest. Cells trailing behind MCS after it's left areas especially on eastern extent as the lapse-&rates are allowed to re-strengthen as surface heating is still occurring.

Moisture also feeds those trailing cells from the far SW where it combines with lapse-rates in Wales ish area. Rising moisture feeding into the surface heating and colder air feeding lower and lower in the atmosphere but surface heating weaker. Stronger low-level and deep-layer shearing but weaker energy and forcing.

Supercell potential would be better if initiation if the MCS is slightly earlier and allowed for better heating, instead it remains about even with the MCS's with the southern part having a Supercellular risk given the rising warm air into the southern portion and open air below allowing a few momentum induced to southern portions of the system with cells combining into the system. Potentially the best hail chance along this portion of the system. Lift with rising motion is increased and energy lifting with that rising motion. Therefore updraft speed is increased and with cells pushing into the southern part of the likely MCS, either one, the increased updraft width will also help hail production and if it weren't for the mess with not knowing where it will be, it would likely have high risk lightning frequency, very frequent lightning possible and more severe risks associated with the southern part of either of these two or combined systems. 

[Daniel_c150311]

I dont know how to describe the dije here but its like skys full of "dots" of clouds and are now starting to rise 

 

 

 

Edited May 12 by Daniel_c150311

[Azazel]

Too far south and east here but some lovely Accas filling the sky. The heat goes out with a whimper for us as usual 

[Cain]

Either way I’m in a good place to due to elevation 

[Cain]

Also very hot and humid here now 

[neil_b]

Can’t work out whether the Marches is prime position or whether we’re more likely to see the real developments take place both east and west of the border.  Here’s hoping for something in any case.

[Karl83]

Warming up nicely here... hoping I won't need to travel too far today!

[ChannelThunder]

Noted the Accas fields earlier too. Timing would suggest that was what was left of the 'plume' models showed earlier in the week!

[Cain]

Feels much humid out there and hot in the sun now 

[Turquoise]

We are in one of the highest risk areas this afternoon, hopefully this time it delivers. Not had a good storm up here in almost 4 years now....current observations, feels humid, milky high cloud and some accas this morning, cloud cover around 80% but thin layers still allowing hazy sunshine to sneak through. The signs are certainly good.