eddied
24 June 2019 20:55:35

Can anyone explain the mechanism at play here? I mean, the sun has gone down so the energy source will be running low and it has to make it across the channel, which has a habit of killing off thunderstorms. Why is this cell forecast not to disintegrate that way? What energy is perpetuating it?


Or is it just that there’s energy spare to make the crossing?


Location: Reigate, Surrey 105m ASL

Winter 22/23
Days snow falling: 4
Days snow on ground:8
Max snow depths: 6cm (December 19th ish)

Summer 2022 max 39C on July 19th
Summer 2021 max: 32C on July 18th
Summer 2020 max: 36C on July 31st
Polar Low
24 June 2019 20:56:38

By Velde his worked there for what it seems about 100 years.


 


A level 1 and 2 were issued across western France and southern UK mainly for severe wind gust, large hail and tornado chances, and in Ireland for spout-type tornadoes.

A level 1 was issued across southeastern Europe mainly for large hail and extreme rainfall.


SYNOPSIS

The strong southerly flow east of an Atlantic low has advected a layer with steep low to mid level lapse rates out of the Sahara and Spain northward into central France, where high low level moisture converges in a thermal trough. Meanwhile, southeastern Europe continues to be under influence of an upper cold pool, with relatively weak flow but significant CAPE.

DISCUSSION

...Western Europe...

A level 1 over central France illustrates mainly the uncertainty of storm initiation, where MUCAPE over 1000 J/kg meets 500 m2/s2 0-3 km SREH and 20-25 m/s DLS. Td2m forecast to be 19-21C. Across western France and southeastern UK various models produce precipitation likely from elevated convection along the cold front, with weaker CAPE. The lifting action of shortwave troughs also reaches central France, and relatively weak CIN is calculated on the convergence line. However, models hesitate producing any storm in the otherwise severe weather supportive environment, except for an evening/night MCS developing most likely over Normandy, moving NNE-ward.

Initially convection will start as clusters of cells including rotating ones (supercells) even if elevated base, which can produce very large hail and severe gusts. If rooted in the boundary layer of the surface convergence line, then with 0-1 km shear exceeding 10 m/s and the strong SREH also tornadoes are possible. However, such collocation is not what COSMO model suggests, which keeps nocturnal development west of the line. But if indeed clustering into an MCS over the late evening, a squall line may form with the potential of organized severe wind gusts.


chelseagirl
24 June 2019 20:57:39
The new blitzortung site is good. You can actually zoom in which you couldn’t do before.

http://map.blitzortung.org/#8.02/48.752/-0.545 


The Fenlands of Cambridgeshire
Polar Low
24 June 2019 20:59:25


Originally Posted by: chelseagirl 

The new blitzortung site is good. You can actually zoom in which you couldn’t do before.

http://map.blitzortung.org/#8.02/48.752/-0.545

Arcus
  • Arcus
  • Advanced Member Topic Starter
24 June 2019 21:04:18

Originally Posted by: eddied 


Can anyone explain the mechanism at play here? I mean, the sun has gone down so the energy source will be running low and it has to make it across the channel, which has a habit of killing off thunderstorms. Why is this cell forecast not to disintegrate that way? What energy is perpetuating it?


Or is it just that there’s energy spare to make the crossing?



Elevated storms. Surface energy (SBCAPE) not important. Surface based storms rely on convection based on solar heating at surface levels. In this scenario we're looking at energy available higher up that is getting released thanks to the Heat Low from Iberia that has migrated northward, so it's Most Usable Cape (MUCAPE) being the important index - storms are initiating much higher up in the atmosphere thanks to destabilisation of upper layers releasing all that energy that's higher up. 


Ben,
Nr. Easingwold, North Yorkshire
30m asl
ballamar
24 June 2019 21:10:24
I hope London Underground have their pumps on standby could be a lot of flooding early morning
Polar Low
24 June 2019 21:11:07

its going to be a good night for some 


https://www.netweather.tv/live-weather/radar


 

Polar Low
24 June 2019 21:15:48

If so probably running it on a 10Ma breaker 


 


Originally Posted by: ballamar 

I hope London Underground have their pumps on standby could be a lot of flooding early morning

idot
  • idot
  • Advanced Member
24 June 2019 21:42:56

 


SO ten years ago  😁


Thunderly by Jan Plesek
https://apps.apple.com/gb/app/thunderly/id1341334743




 


Originally Posted by: chelseagirl 

The new blitzortung site is good. You can actually zoom in which you couldn’t do before.

http://map.blitzortung.org/#8.02/48.752/-0.545


howham
24 June 2019 21:49:00
Enjoy guys. Looking forward to reading all the reports in the morning.
thor22
24 June 2019 22:20:09
Might be worth keeping an eye on the Portsmouth Harbour Webcam given the sferic that's just shown off the IOW

http://www.camsecure.co.uk/portsmouth_harbour_webcam.html 
Rob
Marple
SE Manchester
ozone_aurora
24 June 2019 22:25:41

Originally Posted by: Arcus 


 


Elevated storms. Surface energy (SBCAPE) not important. Surface based storms rely on convection based on solar heating at surface levels. In this scenario we're looking at energy available higher up that is getting released thanks to the Heat Low from Iberia that has migrated northward, so it's Most Usable Cape (MUCAPE) being the important index - storms are initiating much higher up in the atmosphere thanks to destabilisation of upper layers releasing all that energy that's higher up. 




Yes, indeed. These elevated storms (medium level storms) feed from warm, humid air in the lower troposphere rather than directly from the surface, which in this case, originates from Iberia as you've said, and stay alive even if it flows over a cool surface. They show much less diurnal variation than surface-based storms and tend to peak in convective activity near midnight.

You could call them Altocumulonimbus. Their cloud base can sometimes be over 3,000 metres, making cloud-ground lightning strikes especially spectacular. Strangely, there's only little info on these in English science.

picturesareme
24 June 2019 22:34:31

Originally Posted by: thor22 

Might be worth keeping an eye on the Portsmouth Harbour Webcam given the sferic that's just shown off the IOW

http://www.camsecure.co.uk/portsmouth_harbour_webcam.html


 


Dry here and that's just heavy rain out there. Thundery stuff remains over frqnce

thor22
24 June 2019 22:41:09
Yes that sferic disappeared, but it's a good cam tho! I would expect those French cells to track N NE. But I've seen this before and suddenly activity can appear out of nowhere with high-based stuff.
Rob
Marple
SE Manchester
thor22
24 June 2019 22:48:18

Excellent post Azura. High-based storms are great for unpredictability and spidery lightning. I remember one in Manchester in the 80s and one travelling from Calais to Paris on a school trip in 1970! Isn't nature wonderful! I probably won't be saying that at 7am with a hangover :)


Rob
Marple
SE Manchester
picturesareme
24 June 2019 22:50:26

Looking like a classic squib fail... storms over france die over channel and just left over rain hitting UK... 'Thundery Rain'


Expect rain, but don't expect more then just the odd flash or rumble here & there.

Weathermac
24 June 2019 22:54:21
Looks like it’s going to miss the midlands and head for se England as usual these days alas.
thor22
24 June 2019 23:14:14
Still tracking N NE albeit slowly. More sferics showing along S Coast.
Rob
Marple
SE Manchester
picturesareme
24 June 2019 23:21:35

Originally Posted by: thor22 

Still tracking N NE albeit slowly. More sferics showing along S Coast.


There's no sferics on the south coast anywhere - they're still over north France and even here they're not very numerous.


This is just going to be a fail. 

thor22
24 June 2019 23:38:01
One near Cardiff and Essex now.
Rob
Marple
SE Manchester
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