Convective / Storm Discussion Thread - 31st May 2017 onwards

[Nick L]

2 minutes ago, John Hodgson said:

Isn't it fairly simple? A low risk of storms in but could be severe if they do form in the black area, and a moderate risk of storms in the orange but not severe likely to be severe. Although a probability of severe would make more sense than a binary. 

It's that last part that puzzled me most. But the accompanying text clears it up a bit more.

Edited June 20, 2017 by Nick L

[Delka]

Happy I got something, main feature was the 15+ minutes of torrential rain with 4 rumbles of thunder

[tomp456]

5 minutes ago, Dami said:

It says only if the cap breaks. So i'm thinking we are either gonna get nothing or it's going to be a biggie. 

I don't think i'm going to be lucky. Hubs surprised me with an iphone7 this morning. That's my luck for today.

estofex is having none of it.

The met says the party will happen tomorrow.

Reminds me of a June day (can't remember precisely the day) either in 2011 or 2012, all the parameters for storms were out of control, unfortunately cap was strong, high cloud rolled in, ruined temperature, so we got nothing. 

Next day similar set up, less cap, lower parameters, and we got a storm

 

 

[Dami]

Yeah my only saving grace is the best storms we have had here weren't forecast. Although it's been a couple of years since a storm woke me and that year we had 3 storms in 3 days.

[Jasper Foxx]

Just caught sight of a 'Severe Weather Updates 2017' page on Facebook who are predicting Supercells and Tornadoes for the UK with these storms.....

Edited June 20, 2017 by Jasper Foxx

[Nick L]

Just now, Jasper Foxx said:

Just caught sight of a 'Severe Weather Warning' page on Facebook who are predicting Supercells and Tornadoes for the UK with these storms.....

Wouldn't rule out a supercell at all looking at some predicted soundings. However, beware of such Facebook groups that are no better than the Daily Express!

[Nick L]

11 minutes ago, Davethedog said:

My interpretation is that it's like when Estofex have a Level 2 in a 15% lightning area - it's probably not going to happen, but if it does happen then it could be rough.

Agreed, there's tons of silly SPC emulations out there, but whoever runs convectiveweather is very good, and is often quite on the money.

Just read that it's Dan Holley, he's a pro so I trust his judgement! 

[LouTaylor]

7 minutes ago, Jasper Foxx said:

Just caught sight of a 'Severe Weather Updates 2017' page on Facebook who are predicting Supercells and Tornadoes for the UK with these storms.....

I wouldn't rule it out entirely the setup is close to 2014  

[Hodgheg]

7 minutes ago, Nick L said:

Wouldn't rule out a supercell at all looking at some predicted soundings. However, beware of such Facebook groups that are no better than the Daily Express!

I've seen a few of my friends with an interest in weather sharing these pages. A few years ago I probably would have done the same thing. The constant let downs eventually teach you to be a bit more sceptical! 

Fingers crossed we may get lucky though. 

Edited June 20, 2017 by John Hodgson

[A.J]

12 minutes ago, Nick L said:

Just read that it's Dan Holley, he's a pro so I trust his judgement! 

aka "staplehurst" on here IIRC

[BrickFielder]

 Yet another tricky potential thunderstorm breakdown coming up, so I thought I would put a few thoughts down about the different aspects I am looking at. The first scenario I am looking at is the possibilities tomorrow afternoon with a warm sector trough moving across the UK.

 Scenario 1.
 During tomorrow light low level winds will begin to swing round to come from a more maritime direction bringing in a little extra moisture. Above this is still the elevated mixed layer with a marked CAP or warm nose at around 800hpa to 850hpa. This CAP  appears to be slightly weaker the further north in the UK you go. Forecast models don't appear to particularly agree about whether this CAP will go and far to often we have seen models predict storms based on knee deep high dew points. We have also seen high instability produce not even a speckle of rain because triggering is not in place or the CAP is stronger than forecast. The extra ingredient I am watching closely is the potential for a little wind convergence (maybe around Oxford) which may trigger a pulse storm. Hodographs are curved marked in the south of England but less so further North so supercell development initially is very questionable. With inflow being curved into the south of any pulse storm then there is potential for a pulse storm to develop a rear downdraft and slowly develop tornado potential. It is not clear cut and parameters are likely to change so the forecast at the minute would have to be classed as a very slight risk. Warm sector troughs in the UK are however one of the scenarios which can produce moderately severe storms in the UK. Best guess is that the east and north east would be favored for storms at the moment.

Scenario 2
 I looking at the cold front and low pressure system moving across the UK in the early hours of Thursday. We have marked vortcity advection, potential for very high cloud tops, but the timing is such that surface temperatures are low. I am thinking there might be a small window of opportunity where the front becomes rooted in the boundary layer sometime between 6am and 10am. So again this would be a very slight risk mainly in the East and North East due to timing.

Summary
 Looks like both a forecasters delight and nightmare. Delight because they get to examine and explore charts and detail they would not normally do. Nightmare because the potential for getting it wrong is very high. My best guess is that for scenario 1 the high level cloud showing up in the warm sector on satellite images may put a damper on things. For scenario 2 then the vorticity driving this scenario looks concentrated further south on satellite images than I would have expected. When in doubt I tend to look at jet stream forecasts and upper level divergence and this looks fairly strong for the early hours of Thursday. I expect a lot more detail to come out as models re-align with actuals and at this point I cannot make an accurate assessment. I don't suppose this was much help, but might point to things to watch.

[Pat Butcher]

Interesting feature on the SRH charts on lightningmaps..

[Robbie Garrett]

42 minutes ago, tomp456 said:

Reminds me of a June day (can't remember precisely the day) either in 2011 or 2012, all the parameters for storms were out of control, unfortunately cap was strong, high cloud rolled in, ruined temperature, so we got nothing. 

Next day similar set up, less cap, lower parameters, and we got a storm

 

 

This was the date (27th Jun 2011), pretty warm day that started off as being 30*C at 8am. CAPE was like something seen in the states and the front stalled, next day it was cloudy and then this came bowling through.

 

 

Edited June 20, 2017 by Robbie Garrett

[tomp456]

4 minutes ago, Robbie Garrett said:

This was the date (27th Jun 2011), pretty warm day that started off as being 30*C at 8am. CAPE was like something seen in the states and the front stalled, next day it was cloudy and then this came bowling through.

 

 

Yeah, that's the one. 

[cheese]

BBC forecast looks good! But they're generally rubbish so we'll probably get nothing, lol. 

[East_England_Stormchaser91]

9 minutes ago, Robbie Garrett said:

This was the date (27th Jun 2011), pretty warm day that started off as being 30*C at 8am. CAPE was like something seen in the states and the front stalled, next day it was cloudy and then this came bowling through.

 

 

A bust for many though in that quite remarkably awful year of summer weather (2011)! 

This was el gordo! Remember staying up all night, only to get sweet bugger all! 

 

[Nick L]

25 minutes ago, BrickFielder said:

 Yet another tricky potential thunderstorm breakdown coming up, so I thought I would put a few thoughts down about the different aspects I am looking at. The first scenario I am looking at is the possibilities tomorrow afternoon with a warm sector trough moving across the UK.

 Scenario 1.
 During tomorrow light low level winds will begin to swing round to come from a more maritime direction bringing in a little extra moisture. Above this is still the elevated mixed layer with a marked CAP or warm nose at around 800hpa to 850hpa. This CAP  appears to be slightly weaker the further north in the UK you go. Forecast models don't appear to particularly agree about whether this CAP will go and far to often we have seen models predict storms based on knee deep high dew points. We have also seen high instability produce not even a speckle of rain because triggering is not in place or the CAP is stronger than forecast. The extra ingredient I am watching closely is the potential for a little wind convergence (maybe around Oxford) which may trigger a pulse storm. Hodographs are curved marked in the south of England but less so further North so supercell development initially is very questionable. With inflow being curved into the south of any pulse storm then there is potential for a pulse storm to develop a rear downdraft and slowly develop tornado potential. It is not clear cut and parameters are likely to change so the forecast at the minute would have to be classed as a very slight risk. Warm sector troughs in the UK are however one of the scenarios which can produce moderately severe storms in the UK. Best guess is that the east and north east would be favored for storms at the moment.

Scenario 2
 I looking at the cold front and low pressure system moving across the UK in the early hours of Thursday. We have marked vortcity advection, potential for very high cloud tops, but the timing is such that surface temperatures are low. I am thinking there might be a small window of opportunity where the front becomes rooted in the boundary layer sometime between 6am and 10am. So again this would be a very slight risk mainly in the East and North East due to timing.

Summary
 Looks like both a forecasters delight and nightmare. Delight because they get to examine and explore charts and detail they would not normally do. Nightmare because the potential for getting it wrong is very high. My best guess is that for scenario 1 the high level cloud showing up in the warm sector on satellite images may put a damper on things. For scenario 2 then the vorticity driving this scenario looks concentrated further south on satellite images than I would have expected. When in doubt I tend to look at jet stream forecasts and upper level divergence and this looks fairly strong for the early hours of Thursday. I expect a lot more detail to come out as models re-align with actuals and at this point I cannot make an accurate assessment. I don't suppose this was much help, but might point to things to watch.

While the wind profiles look reasonable initially tomorrow and early afternoon (i.e. backed at the surface) they seem to lose this through the afternoon, this is why I'm personally hesitant to go too gung-ho with supercell/tornadic forecasts. Birmingham for example at midday tomorrow has reasonable directional shear with backed surface flow:

But this gets lost through the afternoon. This is based on the GFS, going to try and produce some soundings from the EC this afternoon.

Edited June 20, 2017 by Nick L

[Windblade]

1 hour ago, Delka said:

what i find best about this is i didn't expect anything today and already im one of just a few today to already experience something even though im out of the warning zones, currently under a torrential downpour still 

Just missing me by a few miles. My only hope if anything does develop is that the convergence zone drifts just a bit southeastwards.

Edited June 20, 2017 by Windblade

[TJS1998Tom]

Weather warnings are now in place for tomorrow night with Thunderstorms, could be quite intense if it happens as cape levels are still very high on the latest update with the 06z

[alexisj9]

2 hours ago, Nick L said:

Lucky sods!

Not so lucky, still hot and sunny here, with more humidity. Nice little breeze though. high yesterday 27, already 25 today. May even be hotter today as it's only midday.

[Nick L]

Just now, alexisj9 said:

Not so lucky, still hot and sunny here, with more humidity. Nice little breeze though. high yesterday 27, already 25 today. May even be hotter today as it's only midday.

Thankfully I'm in work today, the A/C is my best friend.

[cheese]

18C here with that dreaded North Sea low cloud making a comeback. If the max temperature doesn't exceed 20C then today will be more than 10C cooler than yesterday (30C). You guys are welcome to this rubbish! Would have been perfectly content with low 20s and sunny spells.

Tomorrow looks better, thankfully.

Edited June 20, 2017 by cheese

[tomp456]

It's only 22c here apparently, in the storm free zone. 

[Had Worse]

Looks like the MO website has gone down,  anyone confirm this?

 

[Mapantz]

1 minute ago, Had Worse said:

Looks like the MO website has gone down,  anyone confirm this?

 

Working swiftly for me.