Storms and Convective discussion - 10th April 2020 onwards

[East_England_Stormchaser91]

1 hour ago, Ben Sainsbury said:

My only worry remains that the pressure lies very high throughout Thursday (~1020hPa) and as a result both ICON-EU and ARPEGE not showing any thundery activity at all.

ICON-EU suppressing any convection with pressure exceeding 1022hPa, ARPEGE ~ 1020hPa

NetWx somewhat below 1020hPa hence more widespread thundery activity.

Yes. A strong cap could be the issue to overcome with this one. However, this could lead to a more discrete variety of storms if any areas do manage to break the capping. This would at least make for an easier chase. 

There’s still chopping and changing happening with every run at the moment, and the risk as it stands if anything has nudged south slightly. 

Still a long way to go. Tomorrow night will answer a lot more questions! 

[Thunder and Lightning]

20 minutes ago, East_England_Stormchaser91 said:

Yes. A strong cap could be the issue to overcome with this one. However, this could lead to a more discrete variety of storms if any areas do manage to break the capping. This would at least make for an easier chase. 

There’s still chopping and changing happening with every run at the moment, and the risk as it stands if anything has nudged south slightly. 

Still a long way to go. Tomorrow night will answer a lot more questions! 

I disagree. I don't think that there is much of a cap as you can see in this sounding from SE England, as well as the CIN chart at 15:00 on Thursday. There is also a large trough which should increase the general forcing and make sure that capping isn't so much of an issue.

Edited May 19, 2020 by Thunder and Lightning

[East_England_Stormchaser91]

3 minutes ago, Thunder and Lightning said:

I disagree. I don't think that there is much of a cap as you can see in this sounding from SE England, as well as the CIN chart at 15:00 on Thursday. There is also a large trough which should increase the general forcing and make sure that capping isn't so much of an issue.

I hope you’re correct. 

Anyone remember the infamous El Gordo bust in June 2011? All the conditions seemed to be in place, but barely anything fired due to  excessive cloud cover and a stronger than expected cap. 

Hopefully we get off to a very clear start from 5-6AM to get those temps and Dew points skyrocketing. 

[Supacell]

1 hour ago, East_England_Stormchaser91 said:

I hope you’re correct. 

Anyone remember the infamous El Gordo bust in June 2011? All the conditions seemed to be in place, but barely anything fired due to  excessive cloud cover and a stronger than expected cap. 

Hopefully we get off to a very clear start from 5-6AM to get those temps and Dew points skyrocketing. 

I remember it well. I travelled down into the south-east and stationed myself in Essex. Waited and waited, nothing happened and so I headed home in the early hours of the following morning. A couple of hours later all hell broke loose and the following morning was quite stormy in the south-east if I remember correctly. I remember being proper annoyed

Edited May 19, 2020 by Supacell

[East_England_Stormchaser91]

15 minutes ago, Supacell said:

I remember it well. I travelled down into the south-east and stationed myself in Essex. Waited and waited, nothing happened and so I headed home in the early hours of the following morning. A couple of hours later all hell broke loose and the following morning was quite stormy in the south-east if I remember correctly. I remember being proper annoyed

It sure was painful. A few elevated storms did fire up in the morning, but they were mainly shrouded above North Sea muck piling in on a nagging NE wind! 

I think most of the stuff erupted over Belgium, and ended up seeing a derecho type storm, heading on into the Netherlands. Very frustrating! The beginning of August 2013 was also similar I believe. Not forgetting June 19th 2013 too. That was a huge disappointment!! A big MCS moving out of France looked bang on course to hit London, only then to turn about 60 degrees right and slice through the Strait of Dover and miss us completely!!! 10 hours later, it was in Kiel and Hamburg giving a strobe lighting show! 

Edited May 19, 2020 by East_England_Stormchaser91

[staplehurst]

Timing is key for Thursday - we've mentioned before how both the phasing and shape/characteristics of the mid/upper level trough will ultimately determine how many thunderstorms (if any) develop. Models are handling this trough slightly differently, including between runs of the same model. The overall picture is we have an upper ridge (red dashed line) over the British Isles for the next couple of days, this shunts eastwards as the upper trough (blue-dashed, quite a narrow / sharp feature) slides in from the Atlantic, but is quickly followed by another upper ridge. This means there will be a relatively small window of a few hours where the upper trough will be in a favourable position, before profiles become heavily subsided as the second ridge builds from the west. 

The 4 panel below, of 500mb relative humidity, highlights the differences between each model, and indeed between runs of the same model (ARPEGE etc) with the handling of this trough. Notice how the 00z ARPEGE is way quicker with the trough than it's previous 12z run, and while both the 00z ECMWF and GFS have similar timings for the trough axis, they do have subtle differences in the shape of it. There has been a trend though for this trough to approach slightly faster than previous runs, and this is something to bear in mind if this trend continues (this ultimately shifts the area where storms may develop gradually eastwards). Notice also the marked mid-level dry intrusion (very low RH) immediately to the rear of the trough.

There are two possible storm evolutions for Thursday. Firstly, elevated thunderstorms could develop as the approaching trough cools and moistens the mid-levels, increasing the available instability and providing the forced ascent required to generate elevated convection above the elevated mixed layer (EML). Forecast profiles (below left) suggest this is heavily reliant on the moisture content in the 700-800mb level. Models vary quite a bit at how much moisture may be available in this region, and generally those with more moisture (higher RH) are breaking out elevated thunderstorms, while those that are drier are not.

The ECMWF has been consistently breaking out elevated thunderstorms during the morning hours for several runs now - until today's 00z run which has the 700mb 'moisture tongue' (below right) slower arriving and therefore generally too late to phase in with the passage of the trough. Elevated storms tend to affect a much wider area, so more places would in theory experience a thunderstorm if they developed - but equally tend to scupper potential for surface-based storms later in the day due to excessive cloud and less surface heating.

The second potential is for surface-based thunderstorms, which will require substantial surface heating to overcome the low-level capping inversion. There is likely to be a fairly deep EML, and given surface mixing will likely occur I suspect some of the models are overdoing the surface dewpoints. I've adjusted the second forecast sounding below (somewhere in Essex) for a dew point of 12C, which seems reasonable, but which would require an air temperature of at least 26C to overcome the cap. Assuming the development of a sea breeze / surface low, then moisture pooling along convergent boundaries may lift the dew points up another couple of degrees potentially, and this may lower the required 'trigger' air temperature by a couple of degrees as well. Such low-level convergence would ideally be needed to provide the trigger for deep convection to occur.

This particular forecast profile is very dry (but it is based on the 00z ARPEGE which I feel is clearing the trough through too quickly - the alternative was to use a GFS forecast profile which is excessively moist, a known bias in the model), and so one issue is potentially the lack of moisture aloft to sustain convection. There is some reasonable speed shear, which would help separate updraft/downdrafts and combined with potentially significant CAPE would aid in storm longevity. As such, some fairly large hail would be possible. The high cloud base (due to the large surface temperature/dewpoint spread) would severely limit the tornado potential, unless bases were able to lower once convection gets going and the boundary layer moistens somewhat. Low-level winds may become increasingly backed, especially later in the afternoon, as sea breeze / heat low develops. 

 

 

So, to summarise - concerns exist over the timing of the mid-level trough (if it continues to speed up then it may move through too quickly for peak diurnal heating). Forecast profiles also look quite dry, and so deep convection may struggle to develop - especially at first. But IF surface-based storms do develop, then they could produce some reasonably large hail. And there is a chance of elevated storms developing late morning onwards, depending on how much moistening occurs in the mid-levels - but this may scupper, or at least limit in areal extent, the potential for surface-based storms in the afternoon.

In essence, lots to play for, much of which is determined by the shape/timing of the upper trough...

Edited May 19, 2020 by staplehurst

[Thunder and Lightning]

I don't know why but I much prefer to have a severe storm with good structure and more intense weather than a lightning show, so I am hoping that the elevated morning thunderstorms do not develop and 'ruin' the environment. 

Edited May 19, 2020 by Thunder and Lightning

[Flash bang flash bang etc]

I only really use Ventusky at the moment (due to time contstraints) but this is predicting activity to break out from about 8am (hush hour on the roads) which is no good for me cos I’ll be on the way to work

If it started a few hours earlier - say 4am - that would be perfect, also I’ll be headed NE into NE London, plus would be a chance skies could clear by early afternoon and set us up for a round 2 over London and southern parts of Essex

 

 

[Harry]

26 minutes ago, staplehurst said:

Timing is key for Thursday - we've mentioned before how both the phasing and shape/characteristics of the mid/upper level trough will ultimately determine how many thunderstorms (if any) develop. Models are handling this trough slightly differently, including between runs of the same model. The overall picture is we have an upper ridge (red dashed line) over the British Isles for the next couple of days, this shunts eastwards as the upper trough (blue-dashed, quite a narrow / sharp feature) slides in from the Atlantic, but is quickly followed by another upper ridge. This means there will be a relatively small window of a few hours where the upper trough will be in a favourable position, before profiles become heavily subsided as the second ridge builds from the west. 

The 4 panel below, of 500mb relative humidity, highlights the differences between each model, and indeed between runs of the same model (ARPEGE etc) with the handling of this trough. Notice how the 00z ARPEGE is way quicker with the trough than it's previous 12z run, and while both the 00z ECMWF and GFS have similar timings for the trough axis, they do have subtle differences in the shape of it. There has been a trend though for this trough to approach slightly faster than previous runs, and this is something to bear in mind if this trend continues (this ultimately shifts the area where storms may develop gradually eastwards). Notice also the marked mid-level dry intrusion (very low RH) immediately to the rear of the trough.

 

Thank you as ever for the fantastically informative and educational update @staplehurst - much appreciated!

I personally am just looking forward to the heat, some humidity and threat of stormy weather. If current thinking (eg the current D4 convective outlook) materialises, chances are I’ll be staring up the rump of developing storms as they develop overhead and grow more upscale towards Essex and EA region - possibly some rumbles but more likely some stunning cloudscapes to my N/NE. This thing happens an awful lot in this neck of the woods (London/Kent borders)

[Paul Sherman]

Yep great Forecast there Dan and really goes into detail about timings etc

But this is the Uk and if it can go wrong it WILL go wrong

MCS it is then after early Elevated Storms congeal and move North East - Hahaha

[staplehurst]

3 minutes ago, Paul Sherman said:

Yep great Forecast there Dan and really goes into detail about timings etc

But this is the Uk and if it can go wrong it WILL go wrong

MCS it is then after early Elevated Storms congeal and move North East - Hahaha

You know the annoying thing is, if this were the U.S. you could easily shift the risk areas 50-100 miles east-west and no-one would notice. Being a relatively small island surrounded by water means (surface-based) storms either happen or don't, rather than just shifting the risk to the east - there's no happy medium. Frustrating to say the least! 

Edited May 19, 2020 by staplehurst

[ChannelThunder]

Well, that's Thursday booked as leave from work. Might be hitting the road early and home by mid-afternoon looking at the timings! 

[Zak M]

3 hours ago, East_England_Stormchaser91 said:

I hope you’re correct. 

Anyone remember the infamous El Gordo bust in June 2011? All the conditions seemed to be in place, but barely anything fired due to  excessive cloud cover and a stronger than expected cap. 

Hopefully we get off to a very clear start from 5-6AM to get those temps and Dew points skyrocketing. 

I may have faint memories of that.

Why was it named El Gordo anyway?

[Mitch the motorbike storm]

looking at the forcast.... i dont think broadstairs will get any storms . think more northbound is where the storms are

 

[Paul Sherman]

19 minutes ago, staplehurst said:

You know the annoying thing is, if this were the U.S. you could easily shift the risk areas 50-100 miles east-west and no-one would notice. Being a relatively small island surrounded by water means (surface-based) storms either happen or don't, rather than just shifting the risk to the east - there's no happy medium. Frustrating to say the least! 

Yh exactly its all about landmass and lack of it. The Elevated Storms we would not even bat an eyelid at whilst asleep at the hotel and we would be awaiting the time to recover for surface based storms in the Afternoon area probably with an Outflow Boundary left over from the Elevated Storms that would have raced off as an MCS. Ah well even a Cg at this stage would do me.

Will Message you on Fb to see if your out playing anyway Mr Hollybobs

[Nick F]

Thanks for your detailed insight Dan for Thursday, indeed, timing of the passage of the upper trough not ideal, need it to be delayed a little more to realize best potential.

Nonetheless, 06z UKV still developing some lively cells through the morning across SE England before clearing NE over E Anglia into early afternoon, maybe elevated storms though, given trough moves through before peak heating

Some reasonable deep layer shear coming into play from the west which may organise storms to increase hail threat into the afternoon. 

[Harry]

9 minutes ago, Nick F said:

Thanks for your detailed insight Dan for Thursday, indeed, timing of the passage of the upper trough not ideal, need it to be delayed a little more to realize best potential.

Nonetheless, 06z UKV still developing some lively cells through the morning across SE England before clearing NE over E Anglia into early afternoon, maybe elevated storms though, given trough moves through before peak heating

Some reasonable deep layer shear coming into play from the west which may organise storms to increase hail threat into the afternoon. 

The (presumably) storms breaking out across N France/IoW on the 12z there Nick suggest something potentially more widespread. Number of models have been suggesting initiation inland from say London/Reading then moving generally NE/NNE. If that model were to verify however it could bring more areas of the SE quarter into play - fingers crossed.

[Eagle Eye]

looks like i might get some good pictures from the tailend of the storm

[Thunder and Lightning]

We all need to wait until the actual day and then start getting fully ready, as a lot matters on timing as other people pointed out. I'm personally hoping the trough is slower than expected so that there is a higher chance of surface based storms, but I hope you get some great pictures either way!

[shaky]

24 minutes ago, Nick F said:

Thanks for your detailed insight Dan for Thursday, indeed, timing of the passage of the upper trough not ideal, need it to be delayed a little more to realize best potential.

Nonetheless, 06z UKV still developing some lively cells through the morning across SE England before clearing NE over E Anglia into early afternoon, maybe elevated storms though, given trough moves through before peak heating

Some reasonable deep layer shear coming into play from the west which may organise storms to increase hail threat into the afternoon. 

Interesting thing i see on these charts are the highest cape is much further west compared to where the precipitation develops!how does that work?highest cape is central southern england and into central east midlands!!

[Paul Sherman]

Looking more and more like an early start for chasing. 6z to 12z Madness. Anything for a Cg though. Early night Wednesday for me and up and out early Thursday

[Thunder and Lightning]

Slightly annoyed at the prospect of morning storms. It means I can't film/track etc.

[The PIT]

Well we are well out of the firing line here and even if weren't nothing would happen Local forecast light showers if we are lucky.

[Harry]

Noting all the comments re morning storms. I am so storm starved I’ll take anything I can get right now

[whitty-southwest-uk]

Just now, Harry said:

Noting all the comments re morning storms. I am so storm starved I’ll take anything I can get right now

Haha I’m with you on this. Morning or evening if it’s good enough I’m in it!!!