Storm & Convective Discussion 12z 21/7/14 ------>

[Nick F]

The shortwave feature just south of Iceland this morning looks to swing SE across Ireland then southern UK on Thursday bringing a greater risk of thunderstorms after a lull today ...

Edited August 13, 2014 by Nick F

[Chris K]

The past couple of days have reminded me of early Spring storms. Brilliant "clean" convective skies with towering clouds and temperatures that dropped like a stone under the rain. On Sunday evening there was a row of 4 anviled cumulonimbus clouds following each other, which looked stunning as the sun began to set. I wish I had a camera with me to take a picture.

 

The North Bristol area has in particular seen plenty of torrential showers. Not much thundery activity but a "Bristol Channel Streamer" was in full effect on a couple of days. If only it were winter, as that could of delivered a tidy bit of snow if it was cold enough...

Edited August 13, 2014 by Chris K

[BrickFielder]

 Yes vorticity center south of Ireland with some pretty cool dry air aloft should move towards the UK on Thursday.

 

Some low level convergence suggested on some models and a little divergence at the upper levels as the upper trough moves through.

 

Key points are that storms are likely to be slower moving, have a good height to the tops and may benefit from diurnal heating (although temperatures are rather low) inland.  Upper layers look quite moist on current models, so messy convection possible perhaps even an MCS (cloud bases a little too high). Moderate instability for the UK.

 

I think there would be a risk of localized flooding, posibly some hail if any isolated storms develop and lightning.  I dont think wind shear is in place for tornadoes or super cells, but would need to look at low level wind convergence zones closer to tomorrow.

 

To early to put much detail on it and looks like a slight risk of storms. Worth keeping an eye on for slow moving heavy rainfall and to a lesser extent lightning.

 

Steepish lapse rate through the zero degree isotherm.

 

[Neilsouth]

Heavy shower here, big drops! Just got soaked

 

Was there any forecasts here for today?

[Greeny]

Heavy shower here, big drops! Just got soaked  Was there any forecasts here for today?

There wasn't anything significant forecast for today. It was kind of borderline. Only perhaps some isolated showers in places but not many. We got a brief moderate shower here. Could see convection all day so I knew there would be some rain about. But with cape values being low and lifted index being 0 at worst you must have been very unlucky!

[Knoxgar]

servere thunderstorms on 10.8.2014 here

 

my pics just before the hit: http://www.wzforum.de/forum2/read.php?2,2915549,2917157#msg-2917157

 

some videos of the thunderstorm (bow echo, gusts reached 122 kph)

 

 

 

 

public parks still closed due massive damage (thousand of trees down, flooding)

Edited August 13, 2014 by Knoxgar

[Arnie Pie]

Great set of videos Knoxy.....scary but exhilarating at the same time
Thanks for posting

[Knoxgar]

Great set of videos Knoxy.....scary but exhilarating at the same time

Thanks for posting

 

thx arnie, sry for posting them so late, but i was busy^^ was a great t-storm (btw the 58th this year), but alot of damage!

[RazorRob]

Hey Guys,
 
I appreciate these are a tad late and not sure if this is the right place to post, but kept forgetting to upload them.
 
Both videos are from the Imported MCS that hit the Sussex & Kent coast on 18th July 2014. The first video is of the storm approaching and structure. The second is after I was hit by the initial gust front and nearly lost my tripod across the road, I then ran for cover and started recording once I got into my car which was hidden behind the sea wall/bank.
 
After the storm passed through I found several trees down and lots of large branches / parts of trees in the road. Unfortunately I did not have anything with me to measure the wind speeds at the time (rectified that now).
 
I took a lot of photos, it was a beautiful storm
 

 

 

[RazorRob]

I was very lucky to get some amazing photos of the storm, and then later that night we had a second storm and the lightning was immense...

 

 

 

 

Camber Sands Wind Turbines:

 

 

 

It was a long night and finally got to bed at about 5.30am lol - WORTH IT!

 

More Piccys here: http://s1299.photobucket.com/user/razorfagg/slideshow/

[Bluebreezer54]

I was very lucky to get some amazing photos of the storm, and then later that night we had a second storm and the lightning was immense...

 

 

 

 

Camber Sands Wind Turbines:

 

 

 

It was a long night and finally got to bed at about 5.30am lol - WORTH IT!

 

More Piccys here: http://s1299.photobucket.com/user/razorfagg/slideshow/

Hello and welcome RazorRob. Some tremendous video and photo's there and thanks for sharing them. I was on the seafront at Hastings when that beast of a storm struck and also have some video of it which I will try and post here.

 

In all my years of watching storms in the UK I can honestly say I have never seen anything quite like that as it approached across The Channel that Friday evening. The storm which followed and hit the south coast a few hours later was spectacular for it's lightning display, and went on for over 2 hours. Epic event.

Edited August 13, 2014 by Bluebreezer54

[vladthemert]

amazing vids pics posted there RazorRob  and Knoxgar.

 

Going to love tomorrow Estofex up we got level 1 warning for east coast this what they say this could be very bad, lots of moisture with slow moving storm.

 

http://www.estofex.org/

 

North Sea, British Isles, northern France

In the range of the trough axis, weak winds, rich moisture, and rather high low-level buoyancy are expected to increase the chance for non-supercell tornadoes. Additionally, slow moving storms may produce excessive precipitation, especially along the land-sea-breeze convergence over eastern England, late in the period also over northern France, Benelux, and Germany.

 

[Mapantz]

Nice one Knoxgar and RazorRob- great pics and vids. Thanks for posting them.

[Panayiotis]

Possible squall line setting up from Bristol to Barnstable...

Edited August 14, 2014 by Panayiotis

[Raidan]

Think I just heard thunder.

[Supacell]

Another round of showers and thunderstorms today, difference being is that today I am not glued to one spot and am able to go out there and chase from midday onward. However, uncertainties as to where is the best place to go, lets investigate why.

 

Using the GFS suite, CAPE and LI values are showing enough instability to allow thunderstorms to develop, this especially so across southern parts. In general the WRF and NMM agree with this scenario and show best instability across the southern half of England (Midlands southward). This is not to say that the CAPE values further north are not enough for storm formation, but looks weak on GFS and even weaker on NMM.

 

 

However, lapse rates are up almost countrywide but once more best from the Midlands south. TT index (which is useful to indicate storm coverage) is also quite high countrywide at over 50 which would indicate quite numerous thunderstorms. 

 

 

 

The bone of contention for me is the wind maps, showing an obvious convergence zone down the eastern side of England as westerly winds meet sea breezes from the east coast. A convergence zone like this will tend to focus showers and increases the risk of storms as the converging winds help to drive the development of big clouds high into the atmosphere. This also brings the risk of funnel clouds and weak convergence tornadoes. There is another convergence zone across southern England, this running through the area of higher CAPE. NMM shows a strong convergence zone across London and the SE.

 

 

 

ELT's are very high, and so hail and lightning likely to be fairly prolific in storms that do develop. I would not expect large hail, but rather a lot of small hail in many of the showers and storms today (up to 1.5cm diameter).

 

Shear is weak today, and so organisation of storms may be reliant on convergence zones. My thoughts are that there will be numerous pulse storms across England, especially the Midlands southwards. Where these storms do occur they could briefly produce frequent lightning, hail and gusty winds. Storms will also be slow moving so a risk of flooding where storms line up - and this is more likely across areas with wind convergence, so eastern England especially. 

 

In conclusion I would expect the most numerous storms to be over Eastern England today, especially E Yorkshire, Lincolnshire and into East Anglia and the SE. However, I would expect sferic activity to be higher across the southern half of England from the Midlands southwards in any storms that get going, but storms more dis-organised here than further north. This afternoon the convergence zone forecast across CS England may come into play and allow storms to focus in an area near to the southern Midlands/London and the SE.

 

There is a risk of thunderstorms pretty much countrywide, but the areas mentioned have the highest risk IMO. For me, I think I would go for somewhere in the SE Midlands/London this afternoon and then perhaps SE England for the evening period for the overall sweet spots for getting a good storm with lightning. Storms look to rumble on into the night across eastern coastal areas. I await a more experienced forecasters opinion later.

Edited August 14, 2014 by Supacell

[SteveB]

Thunderstorm rumbling away just to the South of me right now, so it looks like things are kicking off already.

[TonyH]

Sferics over Ceredigion some 10 miles to my north so too far off to hear thunder.

[Evening thunder]

It was looking good for here but now the CAPE moves/develops just east of me before peak heating once again.. :/ Wonder if the GFS could be wrong and it will be a tad further west.. probably not.

[Harry]

Quite an exciting day ahead me thinks

 

One of those classics where I think some will get a train of 3-4 thunderstorms on the trot, whilst others may not get to see much.

Edited August 14, 2014 by Harry

[Nick F]

Storm & Convective Forecast

Issued 2014-08-14 08:29:11

Valid: 14/08/2014 0600z to 15/08/2014 0600z

 

 

THERE IS A RISK OF THUNDERSTORMS FORECAST

Synopsis

Upper trough overspreads much of northern Europe, the trough axis lying south through the N Sea into Germany/Low Countries - shifting E into NE Europe today. A shortwave trough originating from Iceland area arrives across southern Britain during Thursday, increasing instability and risk of thunderstorms.

 

... IRELAND, ENGLAND, WALES and S SCOTLAND ...

 

A shortwave trough/vorticity max moves SE across Ireland and southern Britain this morning on the western edge of broad upper trough. Moderate instability will develop across much of the UK through the day, as cold mid-level air arrives with shortwave trough and modest surface diurnal heating increases through the day. Large scale ascent with approaching shortwave and local convergence zones of light low-level winds just east of the Pennines and also across central/southern England will support clusters/lines of storms, despite background of weak deep layer shear. Large localised rainfall totals in a short space of time from slow-moving t-storms will be the main hazards - with the risk of flash flooding. There may also be isolated marginally large hail events (hail to 2cm diameter), given steep lapse rates. Weak winds aloft, surface convergence of moist air and strong low-level bouyancy may support the development of funnel clouds which may briefly reach the ground as weak tornadoes or waterspouts. Storms may continue through the night across coastal areas, given warm SSTs and cold mid-level temps.

Edited August 14, 2014 by Nick F

[TonyH]

Absolutely torrential rain here past 15 minutes, 123mm/ hour one of the highest rates I have had here!

[Arnie Pie]

 was a great t-storm (btw the 58th this year)

Thanks for that

 

Meanwhile back in Brum heavy showers passing through atm.....may get some T&L later.. allthough i`m not here for most of the day

Edited August 14, 2014 by Arnie Pie

[Evening thunder]

Already had some heavy/torrential showers this morning, better than northing. Top rain rate 79mm/hr. According to ATD it's started producing sefrics east of here lol

[TonyH]

10mm in just 15 minutes, 17mm past hour, eased atm, no thunder, road awash.