Storms and Convective discussion - 16th June 2021 onwards

[davehsug]

1 hour ago, Ruck Bodgers said:

B&Q at Meir Park got absolutely flooded, with customers having to evacuate with the water going above their feet, the flooding and rain was that intense!!

Yep, hard to believe that just 3 miles away it stayed bone dry!

[Met4Cast]

10 minutes ago, Mapantz said:

Except, not for us.

Models say different. 

Might not be a plume in a classical sense of the word, but higher theta-e moving northwards associated with the elevated thunderstorms tomorrow night is for me, a plume event.  

[Tim Bland]

ECM for Sunday afternoon looks good. Hopefully more storms and rainbows like Tuesday..

[Mapantz]

2 minutes ago, Met4Cast said:

Models say different. 

Might not be a plume in a classical sense of the word, but higher theta-e moving northwards associated with the elevated thunderstorms tomorrow night is for me, a plume event.  

We've had that numerous times in the past few months, does that mean we've had numerous plume events? I've not seen anyone mention it... so it looks like we're now calling anything that comes up from the South, a plume?! 

Edited July 22, 2021 by Mapantz

[Arnie Pie]

29 minutes ago, Arnie Pie said:

To old and wise to start poking the plume nest

Oops

 

[Met4Cast]

10 minutes ago, Mapantz said:

We've had that numerous times in the past few months, does that mean we've had numerous plume events? I've not seen anyone mention it... so it looks like we're now calling anything that comes up from the South, a plume?! 

Nope, only when it comes up from the Spanish plains. 

Edited July 22, 2021 by Met4Cast

[Weather-history]

Timelapse today looking eastwards, convection gets going and finally a storm develops

 

[Ben Sainsbury]

4 minutes ago, Mapantz said:

We've had that numerous times in the past few months, does that mean we've had numerous plume events? I've not seen anyone mention it... so it looks like we're now calling anything that comes up from the South, a plume?! 

I mean that is what a plume is, in simple terms for UK sense "the advection of warm air from the south"?

Edited July 22, 2021 by Ben Sainsbury

[Turquoise]

wouldn't get excited about this so called 'plume'. It will be this............a mass of heavy rain moving northwards whilst the South East (as always) get the lightning .

I really wouldn't get excited.

[Mapantz]

3 minutes ago, Ben Sainsbury said:

I mean that is what a plume is, in simple terms for UK sense "the advection of warm air from the south"?

**Southerly airflow**

We don't see any of that.. maybe by Saturday, but that will be a cooler airmass by then.

[alexisj9]

3 minutes ago, Azuremoon2 said:

wouldn't get excited about this so called 'plume'. It will be this............a mass of heavy rain moving northwards whilst the South East (as always) get the lightning .

I really wouldn't get excited.

Except I don't think it'll move north, more like stay south of the Midlands. 

[Met4Cast]

Not sure where the "south-east will get all the lightning" comments are coming from personally, greatest risk of lightning to me looks IOW westwards, particularly Doset > Exeter.

Looking at skew-t's, areas east of the IOW for example have less mid-level instability compared with areas further west. 10pm-4am likely to be when the main action kicks off, assuming it does kick off. 

Nevertheless CAPE is rather skinny across all areas, so it'll be interesting to see how much lightning we manage to see. Here's @Ben Sainsbury and my convective forecast.

[Harry]

18 minutes ago, Met4Cast said:

Not sure where the "south-east will get all the lightning" comments are coming from personally, greatest risk of lightning to me looks IOW westwards, particularly Doset > Exeter.

Looking at skew-t's, areas east of the IOW for example have less mid-level instability compared with areas further west. 10pm-4am likely to be when the main action kicks off, assuming it does kick off. 

Nevertheless CAPE is rather skinny across all areas, so it'll be interesting to see how much lightning we manage to see. Here's @Ben Sainsbury and my convective forecast.

I think that’s a pretty fair shout @Met4Cast and @Ben Sainsbury.

The interesting complication here is that most models are indicating that the best instability, by around 03z - 08z, will be further east. But, the best engagement between the plume and the trough will be further west - as we know, instability is of little use without a trigger. 

I think that forecast is pretty spot on between 10z and 04z - but I’d extend both zones further east for between 04z and 09z. Saturday day/night and Sunday then become more complicated with areas of reasonable instability, fronts and troughs spiralling around. 

[Met4Cast]

3 minutes ago, Harry said:

I think that’s a pretty fair shout @Met4Cast and @Ben Sainsbury.

The interesting complication here is that most models are indicating that the best instability, by around 03z - 08z, will be further east. But, the best engagement between the plume and the trough will be further west - as we know, instability is of little use without a trigger. 

I think that forecast is pretty spot on between 10z and 04z - but I’d extend both zones further east for between 04z and 09z. Saturday day/night and Sunday then become more complicated with areas of reasonable instability, fronts and troughs spiralling around. 

Just on your last point, the graphic runs up until 6am on Saturday, completely agree that the risk becomes more widespread into Saturday morning, we'll have a separate forecast covering that, just waiting for tomorrows runs before trying to nail anything down  

Tomorrow night will certainly be an interesting one!

[chapmanslade]

42 minutes ago, Mapantz said:

**Southerly airflow**

We don't see any of that.. maybe by Saturday, but that will be a cooler airmass by then.

Don't confuse surface flow with flow of airmass at 850hpa which is where the storms will be based.

This isn't like other more recent events but the ingredients are there

[Harry]

Estofex gone with an early forecast for Saturday into early hours Sunday…

... S-UK ...

Slow moving convection within the deformation band brings high rainfall amounts. Good ventillation aloft and a mean storm motion of 5 m/s should support a few heavy rainfall reports although a weakening/decoupling inflow from Benelux should keep this risk in check. EPS data has a few higher members, but otherwise nothing to justify a level area for now. Could see a small upgrade, if more aggressive IFS verifies (right now still an outlier) but general progressive nature of this deformation band should keep these probs. low.

 

 

 

[Mapantz]

2 minutes ago, chapmanslade said:

Don't confuse surface flow with flow of airmass at 850hpa which is where the storms will be based.

This isn't like other more recent events but the ingredients are there

I wasn't, but there isn't a southerly flow at 850..

[Harry]

@staplehurst forecast hot off the press…

 

Day 2 Convective Outlook

VALID 06:00 UTC Fri 23 Jul 2021 - 05:59 UTC Sat 24 Jul 2021 

ISSUED 21:40 UTC Thu 22 Jul 2021

ISSUED BY: Dan

An active day of thunderstorms is anticipated across portions of the UK and Ireland on Friday/Friday night. A negatively-tilted longwave upper trough over the Atlantic will continue to lift northeastwards through this forecast period as the upper ridge, which has been dominant over the past week, becomes distorted and migrates northeastwards. The resultant strengthening easterly flow across central/southern Britain will shift a relatively high Theta-W airmass from over England and Wales westwards to Ireland, resulting in more stable profiles over Britain and increasingly unstable profiles over Ireland. During the evening and night hours, a more substantial Theta-W plume will slowly advect from France across the English Channel and southern England, with increasing instability here as a result.

 

... IRELAND ...

Diurnal heating of moist low-levels (dewpoints could be as high as 17-19C in places, with air temperatures once again locally exceeding 30C) will yield substantial SBCAPE, potentially >1,500 J/kg. Gradual cooling aloft and lowering heights as the main upper low over Biscay slowly approaches from the south, combined with low-level convergence and some forced ascent over high ground will all contribute to scattered thunderstorms developing from around 12-13z. These are expected to become more numerous through the afternoon and early evening as they drift gradually WNW-wards.

 

Profiles suggest fairly unidirectional winds with height, with some modest flow in the mid-levels contributing to marginal wind shear, but the magnitude of CAPE coupled with a marked dry layer in the mid-levels suggests some active thunderstorms are likely, with frequent lightning and the potential for large hail 2-4cm in diameter. In fact, the strongest cells may perhaps display some transient supercellular structures. Strong outflow winds could gust over 50mph locally, and substantial cold pooling may develop in western Ireland later in the afternoon resulting in several daughter cells developing in clusters nearby. Most thunderstorms will likely decay during the mid-late evening, however some may persist and/or additional cells develop across Munster perhaps even into the early hours of Saturday. Given PWAT of 30-35mm and the potential for training of cells, flash flooding will also be possible.

 

... SW SCOTLAND / CUMBRIA / WEST WALES ...

Diurnal heating, aided by föhn effect due to a strengthening easterly breeze, will result in temperatures in the mid-high 20s Celsius by the afternoon hours to the lee of high ground. Some build-up of CAPE is anticipated, which coupled with onshore breezes converging with the easterly breeze over the high ground could result in a few isolated heavy showers or thunderstorms developing. These will typically drift westwards/offshore, fastest in Wales due to stronger steering winds. The strength of the easterly wind (especially in Wales) and its ability to hold the sea breeze offshore will affect the potential for isolated thunderstorm development.

 

... CHANNEL ISLANDS / SOUTHERN ENGLAND ...

Throughout the day there is a risk of the odd elevated shower/thunderstorm passing close to the Isles of Scilly and tip of Cornwall, but the main focus begins mid/late afternoon near the Channel Islands onwards. Profiles over NW France appear capped to surface-based convection, and would ideally require surface temperatures closer to the mid 30s Celsius. However, a combination of warm advection/isentropic upglide and forced ascent from divergence aloft as the upper low over Biscay approaches is expected to result in elevated thunderstorms developing, already present over the Bay of Biscay in the morning and these then migrating across the Brest peninsula to the Channel Islands around mid-afternoon. A slow migration northwards is then expected through the evening and night hours into southern England.

 

As is often the case with elevated thunderstorms the exact extent of lightning activity is uncertain; however profiles exhibit potential for deep convection rooted from the 800-850mb layer with substantial cloud-layer shear and dry mid-levels to support some potentially fairly active thunderstorms. The greatest instability and steepest mid-level lapse rates will naturally be towards the eastern half of the English Channel closest to the main untouched Theta-W plume emanating from France. Nonetheless, elevated thunderstorms are likely over the English Channel, perhaps as far west as Devon/south Cornwall initially, but the focus for lightning through the night may become confined to areas further to the east with time as thunderstorms in the west weaken and merge into more generic areas of heavy, convective rainfall with fairly saturated profiles. In fact, it may be the case that very little activity occurs east of the Isle of Wight until the early hours, with the potential for an uptick in activity to develop over SE England (rather than necessarily drift inland) during the early hours of Saturday. 

 

Analysis of cross-section data suggests there may be two main features - the bulk of the thunderstorms along the cold front/occlusion, but scope for more isolated very high-based elevated storms perhaps earlier on a preceding pre-frontal trough. Cloud tops in the most potent storms could get close to 40,000ft, and despite the elevated nature it is possible a couple of storms over the English Channel and into Cen S / SE England may exhibit some transient supercellular characteristics which may pose the threat of some marginally-severe hail. The main hazard, however, will be heavy rain and flash flooding potential, alongside lightning. There will already be a brisk easterly wind through the English Channel due to the existing surface pressure gradient, however brief gusts 50-60mph may be possible near the most intense cells.

 

A MDT has been issued for the Channel Islands for now, but if the forecast evolution remains largely unchanged this may be extended towards Cen S / SE England.

Edited July 22, 2021 by Harry

[ChannelThunder]

Interesting forecast from Dan, a LOT going on there! Let's hope that yellow shading makes its way up to central S England on a later update

[Allseasons-Si]

Evening all

there has been some great post's in here over the last few days,...thanks guys for your hard work because i know how time consuming it is editing videos

@Zak M,them pics/stills are completely true weather porn, will look at the vid later as it's late now but thank you

Finally,...the BoB is lighting up good and proper now with some good cloud tops in there

Satellite images with clouds height of France, Weather in France - SAT24.com

EN.SAT24.COM

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Satellite images with clouds height of France, Weather in France - SAT24.com

good luck down there in the south as it is looking good for tomorrow>>

cheers and have a good weekend.

[Paul Sherman]

Looks very similar to a few weeks back when Lightning will be more prevalent as time goes by on the eastern end of the storms moving north out of France. Expect bright echoes firstly from IOW westwards from 18z to 23z this as Dan says merging into Thundery rain as it makes its way North but regeneration further east as storms push northwards all the way to East Sussex / Kent coast looks likely.

I will be out and about waiting for the early hours show and will not get tempted by a drive towards Hampshire or Dorset, gunna be a long night but hopefully 1 thats worth it in the end if the expected High Based elevated lightning occurs off the coast.

If any others are out good luck and I have my spot in mind already.

[ancientsolar]

do we have any live Cornish Cameras ? Might be able to pick up that lightning  

[Mark -W-s-M]

22 minutes ago, ancientsolar said:

do we have any live Cornish Cameras ? Might be able to pick up that lightning  

Might be able to see on this one 

Sennen Cove Live Webcam

WWW.CAMSECURE.CO.UK

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Sennen Cove live webcam overlooks the beautiful Sennen Cove in Cornwall UK from an ideal location high above the cove in one of the lovely Atlantic Cottage Holidays rental premises. This live streaming webcam from...

 

[ancientsolar]

4 minutes ago, Mark -W-s-M said:

Might be able to see on this one 

Sennen Cove Live Webcam

WWW.CAMSECURE.CO.UK

---

Sennen Cove live webcam overlooks the beautiful Sennen Cove in Cornwall UK from an ideal location high above the cove in one of the lovely Atlantic Cottage Holidays rental premises. This live streaming webcam from...

 

thanks, FPS is a low, but I can see frequent lightning on this cam from the site you linked 

Penzance Harbour Webcam

WWW.CAMSECURE.CO.UK

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Penzance Harbour in Cornwal live webcam showing the beautiful and very interesting views of the slipway, harbour wall and general boating area around the sailing club. You can also just see the church in the back...

 

[Turquoise]

200 strikes a minute of the SW coast of UK right now... Unfortunately most of this electrical activity will fizzle out when the storm hits land