Storms and Convective discussion - 10th April 2020 onwards

[Paul]

5 minutes ago, Met4Cast said:

A few of the pros over on Twitter when the UKV was first introduced onto Extra. I asked about it's known weaknesses/biases. 

We've not seen any evidence of that as yet tbh, and can't say anyone from the Met Office has ever mentioned it to us. Not saying it's not a thing, but have not seen or heard of any reason to think it is so far. 

[Harry]

14 minutes ago, staplehurst said:

THURSDAY NIGHT

Perhaps a more overlooked potential is on Thursday night, as the Theta-W plume that initially gets advected into SE England on Thursday morning, then shunted away to the east, resurges back north on Thursday night from France ahead of the next Atlantic low. There is potential for a second round of elevated thunderstorms developing during Thursday night as this becomes engaged by increased forcing aloft from the west. However, this overall setup is less clear-cut, and so confidence in the forecast evolution is a lot lower. The main area at risk is possibly slightly further north, towards the Midlands / Yorks-Lincs / East Anglia, but I would rather wait a few more model runs given the uncertainties at play as to whether anything will develop or not. Forecast profiles are quite warm/moist in the upper atmosphere, and overall the magnitude of instability is probably less than on Thursday morning.

I did wonder why the overnight minima for Thursday is projected as being quite high for this time of year - 16C for my location. While this does not of itself indicate storms are likely, 16/17C night time temps I usually associate with humid/plume type scenarios! One I’ll be keeping a firm eye on.

Thanks as ever Dan!!!!

As an aside, it’s rapidly getting toasty here. On my 07:20 walk it was 16C, it’s now 22C. Phone app now suggesting a max of 25/26C for here which, if the cloud keeps away, seems quite an underestimation. Said app also now trickling into tomorrow morning and projecting a 40% chance of rain here for around 08:00 tomorrow. 

Edited May 20, 2020 by Harry

[ChannelThunder]

Good to hear there is potentially a second stab at this during more favourable night time hours. I did spot something on the 00z GFS showing that but thought it must have been smoking something.

[Flash bang flash bang etc]

As long as the central southern areas get at least one chance at an event which doesn’t end up occurring in the midlands instead. Already tired of everything being out of reach ... and it’s only May

Edited May 20, 2020 by Flash bang flash bang etc

[Thunder and Lightning]

The latest UKV even more depressing. Not even a shower. I do wish things would turn around but I'm starting to really doubt it

[Paul]

7 minutes ago, Thunder and Lightning said:

The latest UKV even more depressing. Not even a shower. I do wish things would turn around but I'm starting to really doubt it

WOuldn't say that - wind it forward to the early hours of Friday...

[Thunder and Lightning]

I just thought how great it be if we all woke up to a lot better of a setup tomorrow with a CW moderate risk and the conditions we were seeing before. That would be the best...

[Ben Sainsbury]

10 minutes ago, Thunder and Lightning said:

The latest UKV even more depressing. Not even a shower. I do wish things would turn around but I'm starting to really doubt it

Latest EURO4 supports the latest UKV with no elevated nor surface based activity for Thursday.

[Thunder and Lightning]

Just shows how quickly thing can change...

[Zak M]

WOW! Look at the EURO4 for Friday morning!

[Met4Cast]

People are far too quick to react to the models here. 

GFS/ECM/AROME still looking fairly good in terms of storm potential tomorrow morning. Granted, the UKV/EURO4 aren't looking quite as impressive but given storms are elevated, i.e, developing in the mid-levels rather than at the surface, PPN charts from those models won't necessarily be the best indication. 

[Thunder and Lightning]

2 minutes ago, Met4Cast said:

People are far too quick to react to the models here. 

GFS/ECM/AROME still looking fairly good in terms of storm potential tomorrow morning. Granted, the UKV/EURO4 aren't looking quite as impressive but given storms are elevated, i.e, developing in the mid-levels rather than at the surface, PPN charts from those models won't necessarily be the best indication. 

I still think that some storms will develop, I'm just sad that there are not going to be widespread SB storms in the afternoon like some models were previously showing. That's why I still want the trough to slow down, because during most o the day tomorrow I will be doing exams so will not be able to film or track if storms if they are not during the mid/late afternoon.

[Ben Sainsbury]

22 minutes ago, Met4Cast said:

People are far too quick to react to the models here. 

GFS/ECM/AROME still looking fairly good in terms of storm potential tomorrow morning. Granted, the UKV/EURO4 aren't looking quite as impressive but given storms are elevated, i.e, developing in the mid-levels rather than at the surface, PPN charts from those models won't necessarily be the best indication. 

I understand where you are coming from but you have to remember that the GFS and ECM are both low resolution models. AROME is actually on it's own of all the high resolution models with by far the most widespread activity. In comparison (all high-res models but ARPEGE kinda) UKV, EURO4, ICON, ARPEGE & NMM (to some degree) all show little to no activity tomorrow. Even the GFS looks a knife-edge. Despite that I'm a big fan of AROME so you never know.

I don't understand this "PPN charts won't be the best indication" either, you're right in saying they aren't particularly useful for the amount of precipitation that reaches the ground but the greatest lightning activity is associated with the strongest radar returns so if there is no heavy precipitation appearing on UKV/EURO4 then that means no lightning activity regardless of whether it's surface based or elevated.

Edited May 20, 2020 by Ben Sainsbury

[alexisj9]

12 hours ago, Greeny said:

We've been outside all afternoon and this evening (Norwich), it got chilly pretty quickly even though it was pretty damn hot when the sun was out earler. Last night was lovely, felt warm, we were expecting the same this evening but it didnt happen.

We got fog here over night, still spring I guess, the warm air travelling over cold water. 

[Harry]

17 minutes ago, Ben Sainsbury said:

I understand where you are coming from but you have to remember that the GFS and ECM are both low resolution models. AROME is actually on it's own of all the high resolution models with by far the most widespread activity. In comparison (all high-res models but ARPEGE kinda) UKV, EURO4, ICON, ARPEGE & NMM (to some degree) all show little to no activity tomorrow. Even the GFS looks a knife-edge. Despite that I'm a big fan of AROME so you never know.

I don't understand this "PPN charts won't be the best indication" either you're right in saying they aren't particularly useful for the amount of precipitation that reaches the ground but the greatest lightning activity is associated with the strongest radar returns so if there is no heavy precipitation appearing on UKV/EURO4 then that means no lightning activity regardless of whether it's surface based or elevated.

I agree - whenever we’ve had elevated outbreaks the radars/models still signify the precipitation even if it does not make it to the ground. At 10,000ft it might be raining torrentially even if at ground level it’s spotty drops or even completely dry.

[Flash bang flash bang etc]

31 minutes ago, Thunder and Lightning said:

I still think that some storms will develop, I'm just sad that there are not going to be widespread SB storms in the afternoon like some models were previously showing. That's why I still want the trough to slow down, because during most o the day tomorrow I will be doing exams so will not be able to film or track if storms if they are not during the mid/late afternoon.

If it speeds up then we will be seeing elevated storms during the dark hours of tomorrow morning - otherwise it’s going to be somewhere up north Friday night which is no good to anyone that was in the original risk area

[Thunder and Lightning]

2 minutes ago, Flash bang flash bang etc said:

If it speeds up then we will be seeing elevated storms during the dark hours of tomorrow morning - otherwise it’s going to be somewhere up north Friday night which is no good to anyone that was in the original risk area

Still got these to look forward to. I think that I don't really care now about missing out on Thursday considering we have got so much summer left.

[alexisj9]

1 hour ago, Harry said:

Dan’s latest forecast for more especially overnight 

Day 1 Convective Outlook

VALID 06:00 UTC Wed 20 May 2020 - 05:59 UTC Thu 21 May 2020 

ISSUED 06:50 UTC Wed 20 May 2020

ISSUED BY: Dan

Upper ridging largely dominates across the British Isles through Wednesday, and despite some SBCAPE developing over eastern England in response to diurnal heating, profiles are heavily subsided and capped - hence at best some shallow convective cloud is likely. 

Late in the day, showery bursts of rain will spread into W / SW Ireland associated with a cold front. This will continue to track east across Ireland and W Scotland during the evening and night hours, for a time being engaged by a sharpening shortwave approaching from the Atlantic. This may, for a time, increase the potential for some embedded elevated convection, however as the shortwave overruns the cold front the focus will shift to a new corridor of elevated convection that is likely to develop in the vicinity of the Irish Sea / W Britain during the early hours of Thursday - ahead of the cold front. Given rather weak instability, the risk of lightning is considered relatively low but a few isolated lightning strikes may be possible, hence the inclusion of a LOW threat level.

Elsewhere, as the shortwave continues to advance eastwards, by the end of the night it may begin to engage with a plume of high Theta-W advecting from France into Cen S / SE England. Gradual cooling and moistening of the mid-levels, combined with forced ascent, may result in scattered elevated showers develop in the vicinity of the English Channel / S Midlands / S + SE England. As such, a few sporadic lightning strikes may occur late in the night, but the risk is greater beyond this forecast period (i.e. after 06z Thursday). The extent to how much moistening occurs at the 700-850mb level will be crucial in determining how much elevated convection can occur, with disparities between model guidance at present. Nonetheless, a (low confidence) SLGT has been issued to cater for any thunderstorms that develop late in the night, since these could produce fairly frequent lightning given the rapidly increasing instability as the upper trough approaches - initially with very little precipitation reaching the ground until the boundary layer gradually moistens. 

 

Wow some lucky people to my west my get dry lightning tonight. I'm just hoping not to many cgs though, the grass is bone dry. 

[Zak M]

Hmmm. Perhaps we could now see some elevated thunderstorms on Friday morning?

How intense would these storms be if they came off?

[Ben Sainsbury]

9 minutes ago, Zak M said:

Hmmm. Perhaps we could now see some elevated thunderstorms on Friday morning?

How intense would these storms be if they came off?

MU Cape looks to be in and around 300-500J/Kg, some reasonable DLS too of around 10m/s and lapse rates aren't too impressive but nevertheless some sporadic lightning, maybe a touch more frequent in the strongest cells but I wouldn't expect too much. Storms likely to organise into line segments if they do form.

[SnowBlake]

Looking forward to potentially heading out early with my gear to capture some footage as it heads in across the channel. Minimal risk at the moment but I shall set my alarm regularly so I can check out the radars.

Opposite where I live is a sheltered promenade so I can get views from Eastbourne to Dungeness without getting wet.

Anyone else in the Hastings area potentially heading down to the seafront in the morning just in case?

 

[Met4Cast]

The model variability re: storm development is down to the timing & progress of the upper trough moving eastwards. The earlier the front moves in the less chance of storms developing. Models like UKV/EURO4 move the front in earlier during the morning and thus you see little storm development. UKV hasn't exactly covered itself in glory in the run up to this one with some pretty large changes with each run of the model. 

I find lightning wizard to be a pretty good guide, though I believe these charts are GFS based.

Conditions look primed for some decent elevated strom development PROVIDING the trough doesn't move in too early. I doubt this one will be nailed even on tonights runs because the timing is so knife edge, tiny adjustments within the models will mean the difference between showing storm potential & not showing storm potential. Dan highlighted that the moist mid-levels is a vital part of this setup too. AROME is probably what we'd want to be seeing a trend towards on todays runs.

Despite that, I've issued a conditional MDT for parts of East Anglia on my convective graphic. If storms do develop then this where lightning is likely to be most frequent, perhaps into parts of the SE too through the risk diminishing the further south and east of the region you head. Given increasing low-level convergence and the potential for a few isolated SB storms (again, dependent on timing) we could see a few of these becoming locally severe with a small 2-5% risk of weak tornado, especially the further east you head.

However as others have pointed out - The risk is somewhat diminished now. There's still potential, it wouldn't take much for things to swing back in the opposite direction.

Edited May 20, 2020 by Met4Cast

[Flash bang flash bang etc]

I’m seeing that even PJB at UKWW is pondering on a much smaller risk now than was expected. Signals are for the trough to head in at a quicker pace, meaning the risk is less pronounced and the storm activity shifts a little more southward and westward - putting it in a line from Portsmouth up to Cambridge by my estimation. Also means the likely time of initiation is 5-6am - which is ok, but it will be getting pretty light by then

[Nick F]

06z EC seems most keen to break out heavier ppn across Suffolk and Norfolk mid-to-late morning, before clearing out into the North Sea by lunchtime

Ppn and CAPE for 10am

[Zak M]

The MetO's graphics show some action