Convective / Storm Discussion Thread - 31st May 2017 onwards

[East_England_Stormchaser91]

2 minutes ago, Nick L said:

I'm utterly useless at remembering dates of weather events I'm afraid

You know! When Leicestershire and Lincolnshire became Texas for a day! 28/06/2012. 

[Harry]

While I post on here frequently and am a bit of a storm nut, I always struggle to understand how sometimes the atmosphere goes boom, yet with even higher CAPE/DPs and nice CF it does nothing.

I would have thought given the instability and the CF, it would be a perfect setup.....but alas, no! Well....it doesn't appear so anyway. The times I've woken to unexpected thunderstorms when models and media forecasts said not likely ol' chap....

[Ben Sainsbury]

3 minutes ago, East_England_Stormchaser91 said:

Do you think something similar to June 2012 is possible? Given the potential energy? I've never seen SB cape in the UK that high before, ever. 

July 19th (not sure what year) GFS forecasted in excess of 3500 J/kg with -12 Lifted Index, so with this sheer amount of energy available any storms that do develop could be pretty severe.

[Nick L]

Just now, East_England_Stormchaser91 said:

You know! When Leicestershire and Lincolnshire became Texas for a day! 28/06/2012. 

Oh god now I know why I forgot that date. I had moved back to the Midlands from uni in the summer. But over that day I had to go down to London to get my US visa to study in the states...I missed that supercell as it rolled right down the road from home. Was bloody gutted. It's all come flooding back 

Without looking into detail at the set up that day it's difficult to tell.

[Flash bang flash bang etc]

Sea breeze convergence near Welsh coasts and a little bit of a something beginning to bubble around the estuary by the loOks of things:

[StormChaseUK]

Sea breeze helping break the cap West Wales.

[Homerr]

<noob>

What does the 'cap' refer to?

</noob>

[Nick L]

2 minutes ago, Homerr said:

<noob>

What does the 'cap' refer to?

</noob>

Typically, a layer of warmer and/or drier air at lower-mid levels. This essentially has the effect of preventing the warming air at the surface rising any further - if it can't rise to sufficient levels you're not going to get a storm. Now, this can be a good thing for severe storms to an extent. If you release all of the energy uncapped, you can get a thundery mess rather than something more organised. If the cap can hold until evening and break in isolated place(s) you can get isolated, more severe storms. However, if the cap holds, you're not going to get anything. A fine balancing act.

[Homerr]

Thanks Nick this makes sense 

1 minute ago, Nick L said:

Typically, a layer of warmer and/or drier air at lower-mid levels. This essentially has the effect of preventing the warming air at the surface rising any further - if it can't rise to sufficient levels you're not going to get a storm. Now, this can be a good thing for severe storms to an extent. If you release all of the energy uncapped, you can get a thundery mess rather than something more organised. If the cap can hold until evening and break in isolated place(s) you can get isolated, more severe storms. However, if the cap holds, you're not going to get anything. A fine balancing act.

 

[convector]

16 minutes ago, Ben Sainsbury said:

July 19th (not sure what year) GFS forecasted in excess of 3500 J/kg with -12 Lifted Index, so with this sheer amount of energy available any storms that do develop could be pretty severe.

If you're referring to 2014, there was a impressive low-topped supercell that day which passed through oxfordshire. Unfortunately, i don't have the GFS charts for that day, but here's the sounding and radar (i have more photos too, if anyone's interested). If those CAPE/Li values really are accurate for tomorrow, i can only imagine the storms it could support.

Edited June 20, 2017 by convector
Hadn't mentioned these aren't my photos.

[Homerr]

Makes sense with that SKEWT you can see the temperature decreasing as the height goes up but on our current ones it sort of rises a bit half way up - which is our cap?

[Supacell]

19 minutes ago, East_England_Stormchaser91 said:

Do you think something similar to June 2012 is possible? Given the potential energy? I've never seen SB cape in the UK that high before, ever. 

I am hoping something similar to 9th June 2014 happens on Thursday as I am staying directly under the path that huge supercell took

[StormChaseUK]

10 minutes ago, Homerr said:

<noob>

What does the 'cap' refer to?

</noob>

 

Good example towards the end, she breaks through

 

[Homerr]

2 minutes ago, StormChaseUK said:

Good example towards the end, she breaks through

 

Quality!! It makes more sense now thanks

[Arnie Pie]

Just on the subject of the CAP......Is this related to the convective inhibition found on the V4 radar?

if so what do the minus figures represent?

Help The aged please 

 

Edited June 20, 2017 by Nick L

[Marcus_surfer]

Huge towers going up just to my north. To the south blazing clear skies. 29C

[Nick L]

I know that to the newbie, these things look like a big mess of lines, but bear with me. The following Skew-T shows a cap nicely on a very convective day (some of you may recognise the date and location*...), I chose this as it was the first one that came to my head that had a very noticeable cap. 

Concentrate on those two bold, black lines. The right one represents temperature, the left the dew point. The higher up on the graph, the higher up the observations are in the atmosphere (the pressure level is on the left hand side). It's basically a "slice" of the atmosphere. 

You can see at the bottom of these two black lines that they are very close together, representing a very moist surface layer. This maintains up to a level of around 850hPa, but we then suddenly see a change. The temperature line skews to the right, indicating an increase with temperature, and the dew point skews to the left, indicating a decrease in moisture. So we suddenly hit this, warm, dry layer - that's the cap.

This cap essentially stops the warm, moist air at the surface from rising. That is, until the air has warmed and moistened to a sufficient extent that it eventually breaks the cap.

 

*This was the day of the Moore F5 tornado in 1999. We will not be seeing that tomorrow I just want to stress!

Edited June 20, 2017 by Nick L

[Derecho]

Those storms to the North of Swansea have exploded very quickly which certainly shows the cap can be broken!

Unfortunately I think I'm too far South here in Southampton to see anything thundery from this plume, the long wait for a good thunderstorm will continue I expect.

[Marcus_surfer]

Still no lightning from the activity just to the north of me but its not spoiling the sunshine its the only cloud around is these towering cumulonimbus 

[StormChaseUK]

2 minutes ago, Marcus_surfer said:

Still no lightning from the activity just to the north of me but its not spoiling the sunshine its the only cloud around is these towering cumulonimbus 

Any cloud pics?

[Nick F]

24 minutes ago, Harry said:

While I post on here frequently and am a bit of a storm nut, I always struggle to understand how sometimes the atmosphere goes boom, yet with even higher CAPE/DPs and nice CF it does nothing.

I would have thought given the instability and the CF, it would be a perfect setup.....but alas, no! Well....it doesn't appear so anyway. The times I've woken to unexpected thunderstorms when models and media forecasts said not likely ol' chap....

Kind of a loaded gun situation today and tomorrow across England and Wales, yes we have impressive CAPE values of 1500-2500 j/kg, but a cold front and/or surface convergence + strong heating may not be enough to overcome the stout cap in place. The 12z Nottingham sounding shows a warm nose between 750 and 950mb which prevents heated parcels from rising to create CBs.

However, greater forcing for ascent, cooling aloft and falling heights from the west tomorrow afternoon should better allow the cap to erode to allow storms to develop across central and eastern England.

If you are relating to the SE's storm prospects, more of a stronger cap in place today and tomorrow due to closer proximity of upper high to the south over near continent, probably mean any storms staying north of London tomorrow. However, cold front forming over Wales and SW Wednesday night and continued height falls + large scale ascent may bring a threat of storms to the SE on Thursday morning before the fresher air arrives.

My 2 day storm forecast on Netweather website here: http://www.netweather.tv/index.cgi?action=convective;sess=

[Marcus_surfer]

Just now, StormChaseUK said:

Any cloud pics?

I tried uploading but its too big! it all seems very isolated but could develop further east into the midlands

[White Clouds]

Something for Chapel tomorrow then?

[Allseasons-Si]

Well it's busy in here today and i am looking foreward to tomorrows potential as i finish work at 2pm

and by tomorrow night i hope i won't end up like this

 

 

[P-M]

I'm just salivating at the prospects me.  Can't beat a good old lightning display!