Convective/Storm Discussion Thread - 19th May 2018 onwards

[Derecho]

2 minutes ago, tomp456 said:

Lets hope so then! 

Would you put money on it though? 

Hopefully it that precipitation crossing the channel should intensify, then we are on track. We had some thunder here earlier so the cap can be breached! Its gotta hurry up soon though.

[Guest]

Looking to my south the stuff of the Dorset coast is doing nothing.

further afield I’m France the West storm looks like being a Devon and Cornwall event only.

[A.J]

Shame it's not darker as this beast is kicking out a lot of lightning 

[Supacell]

Between Winchester and Southampton. Missed those cells that kicked off here and moved west. Now hoping the Channel fires up or I have had a very harsh bust.

[Super_Uwe]

Tantalisingly close to Salcombe! Can hear rumbling every few seconds but no flashes visible!

[Guest]

Going back home, this is a waste of time for the next few hours.

[PiggiePalace]

And it's moved on - guess that's "edging" your bets!!

 

[Chris K]

What I initially thought was heading this way now looks like staying just to the South of me as they head West. Hoping something develops a bit later behind.

[SteveB]

Storm dieing off as getting close to this area, probably the mendips killing it. 

[TropicThunder]

5 minutes ago, Supacell said:

Between Winchester and Southampton. Missed those cells that kicked off here and moved west. Now hoping the Channel fires up or I have had a very harsh bust.

Wow big respect for that dedication! Hope the channel fires up soon, I'm not giving up hope yet!

[Harry]

Storm has fired off of Dungeness!!

[James86]

7 minutes ago, Supacell said:

Between Winchester and Southampton. Missed those cells that kicked off here and moved west. Now hoping the Channel fires up or I have had a very harsh bust.

Welcome to the south!

[LightningLover]

Strikes in the eastern channel! I REPEAT: strikes in the eastern channel!!

[LightningLover]

Distant elevated thunder!!

[Bristawl Si]

Looks v threatening just a few miles to my SE. Thunder in distance. Rain looks imminent here.

[Derecho]

Blitzkorung starting to show sferics to the ESE of Brighton in the channel, looks like it may be coming together.

[Mapantz]

Quite interesting seeing three troughs via the radar.. no wonder it's all a bit messy!

 

[Bolt from the Blue]

Not good so far. Chased the Dorset cell all the way to Illminster, not one fork was seen, all IC. The storm was moving too fast so given up for now. Hoping the stuff in France will deliver

[Wilxy]

Typical that is dies off as it gets close!

[convector]

Currently heading west along the m4, stopped at membury services when it became clear I wasn't catching those cells near bath. Probably just going to wait until the next wave of storms arrive and go from there. These setups are always so troublesome.

[Mapantz]

According to Mr Grimsley's website, he had a rain rate of 1645.8 mm/hr as a storm passed over.

[Summer Sun]

Storm Forecast
Valid: Sun 27 May 2018 06:00 to Mon 28 May 2018 06:00 UTC
Issued: Sat 26 May 2018 20:02
Forecaster: TUSCHY

A level 2 was issued across parts of S-UK mainly for excessive rain.

SYNOPSIS

Ongoing blocking pattern over Europe results in another active thunderstorm day. This pattern is featured by a substantial upper trough over W-Europe, which is composed of numerous smaller-scale vortices. One vortex just W of the Normandy re-strengthens during the forecast as another impulse from the W merges with that vortex. Another vortex over N-Germany/Denmark weakens/opens up and shifts to the NW over the North Sea. This configuration supports a merging of a SE-ward migrating anticyclone over S-Scandinavia with ridging over the CNTRL-Mediterranean downstream of the aforementioned upper trough. This setup assists in an ongoing advection of a warm/moist and unstable air mass from the Mediterranean towards CNTRL-Europe.
Downstream of that ridge, another upper trough affects far SE-Turkey. CAA occurs east of the Scandinavian high with 850 hPa temperature dropping to below zero.

No well defined synoptic-scale fronts are forecast, so faint mid-level impulses (circling the W-European trough), orography and mesoscale convergence zones dictate the coverage of thunderstorm activity during this forecast. One exeption is a maturing/deforming warm front over S-UK to CNTRL-Germany, which transforms into a wavy and quasi-stationary boundary. This zone with strong LL confluence serves as main focus for more widespread CI.

DISCUSSION

... S-UK, Belgium, Luxembourg, France, S-Alps and N-Italy ...

Areas W/NW of the W-Alps see numerous convergence zones with LL mixing ratios in excess of 10 g/kg. A dominant one becomes established from S-UK to CNTRL-Germany (see SYNOPSIS). Northward fanning EML downstream of the W-European trough overlaps with that rich BL moisture and despite a weakening trend of mid-level lapse rates (partially due to convective overturning from the previous day) robust MLCAPE is forecast in most areas. The majority of models agrees in a broad swath with 1-1.5 kJ/kg MLCAPE while some CAMs indicate even higher values along pronounced convergence zones. A similar moisture/lapse rate setup exists along/S of the Alps/over N-Italy resulting in an analog CAPE magnitude.

An fly in the ointment is ongoing shower/thunderstorm activity from the previous night over S-UK, Benelux/W-Germany to SE-France during the morning hours. This could temper diabatic heating and CAPE magnitude a bit on a regional scale. However most models agree in robust CI with this activity as the environmental CAPE increases during the day.

With weakening mid-level ridging aloft, DLS is meager at best with values in general below 10 m/s. Pockets with stronger mid- or upper-level winds result in regions with 15 m/s DLS or 1-8 km shear (e.g. CNTRL-Germany and S-UK). Enhanced LL flow exists over S-UK with some weakening betimes as the pressure gradient starts to relax. Nevertheless, augmented 0-1km shear and SRH-1 is forecast in that area.

This environment supports robust updraft development during the day with CI linked to diabatic heating, orography, passing mid-level waves and the remnant of overnight convection. Slow moving and even training convection will be a major issue and serious flash flooding could occur due to clustering/slow moving thunderstorms. Over S-/CNTRL-UK, looped but small hodographs indicate a chance for training activity and despite lower CAPE, excessive rain with flash flooding is a distinct possibility. The level 2 areas were issued where ingredients point to more widespread/clustered CI with an attendant enhanced flash flood threat.

Initiating storms also pose a large hail risk despite lack of shear. Betimes, growing cold pools support upscale growth of convection and swaths of strong to severe wind gusts are possible at least on a temporal scale. Beside the rainfall risk over S-UK, some enlargement of the lower parts of the hodograph with 100 m^2/s^2 SRH-1 and LCLs of 600-1000 m also add an isolated tornado risk.

A similar risk for slow moving strong to severe convection exists over the S-Alps and a localized serious flash flood risk beneath slow moving thunderstorms exists - next to large hail. This threat translates to the S betimes and affects NW-Italy during the afternoon/evening. The level 2 was issued where growing thunderstorm tap into rich moisture and a very unstable air mass along/south of the Alps. The level areas were expanded towards parts of SE-France with similar conditions.

http://www.estofex.org/cgi-bin/polygon/showforecast.cgi?text=yes&fcstfile=2018052806_201805262002_2_stormforecast.xml

[Pursuer of Storms]

Spectacular sunset with small cells off in the distance and bubbling convection this evening. Hopefully a prelude of things to come! 

Edited May 26, 2018 by Pursuer of Storms

[Weather roller-coaster]

Gone gusty here not far away

[Azazel]

9 minutes ago, Mapantz said:

According to Mr Grimsley's website, he had a rain rate of 1645.8 mm/hr as a storm passed over.

What ever happened to Grimmers?