Storms and Convective discussion - 10th April 2020 onwards

[BrickFielder]

Potential convective risk Thursday from the occluded front moving up from the south west. While modelling suggests some potential for convective development we should consider that air aloft looks moist perhaps producing a high thin layer of cloud which could dampen down temperatures.Low level wind convergence looks to be in place triggering development which could perhaps create storms behind the upper level disturbance. Combining this with perhaps a warm air inflow from the south and perhaps we could see stronger development. Looking at the skewT forecast profiles then we can see strong wind speed shear in the lower levels, combined with very weak surface winds and convergence which can help with strong inflows. Upper winds look unidirectional and not increasing with height which might limit updraft longevity. Personally I think surface temperatures are too low for strong convection and squally heavy showers might be the order of the day.

[Paul Sherman]

Meto siding with the ECM with regards to early next week and GooFuS out on its own (Pretty Standard) so looking settled now with some decent dry weather for next week.

Ho Hum

[Ryukai]

Well that was an interesting little squall line that just came through, no wind at all, but heavy on the rain.  Slow moving too, took about 15 mins to fully pass over. Can see clear(ish) blue skies on the horizon now with the tops of, what look like, quite large cumulus forming in the distance.

[Harry]

Widely 300 - 700 J/Kg CAPE available tomorrow afternoon and evening.

Let us hope for some fairly widespread thundery activity for the first time this year

[Ben Sainsbury]

5 minutes ago, Harry said:

Widely 300 - 700 J/Kg CAPE available tomorrow afternoon and evening.

Let us hope for some fairly widespread thundery activity for the first time this year

Should actually see some semi-decent lightning activity as a result too!

Edited April 29, 2020 by Ben Sainsbury

[Dreckly]

This coming through now

[Kirkcaldy Weather]

28 minutes ago, Harry said:

Widely 300 - 700 J/Kg CAPE available tomorrow afternoon and evening.

Let us hope for some fairly widespread thundery activity for the first time this year

The 2km is most accurate looks to me like a squall line is a likely outcome tomorrow plenty of vorticity so I would say rotation possible 

[Mapantz]

The 700hPa vertical velocity chart on it's own won't give you much of an idea of whether rotation will occur in thunderstorm/showers. Need to be checking out the Helicity/Shear charts too.

Some pockets of DLS around Southern areas tomorrow - certainly going to be some beefy downpours, but not seeing anything squall-line-like, just a huge rash of showers maybe merging in to longer spells for lucky (or unlucky?) places.

[Flash bang flash bang etc]

I actually have a mornings’ work in Egham. Might hang about for an hour or two afterwards and see if that’s anywhere near a sweet spot

[Allseasons-Si]

I am hoping for some photogenic scenes tomorrow

with some thunder and lightning of course

everything including the kitchen sink at the ready for tomorrow,well erm!,not the wheels

[Eagle Eye]

[Chris Lea-Alex]

Good morning!

Day 1 Convective Outlook

VALID 06:00 UTC Thu 30 Apr 2020 - 05:59 UTC Fri 01 May 2020

ISSUED 07:13 UTC Thu 30 Apr 2020

ISSUED BY: Dan

An upper low and associated cold pool will reside above the British Isles during Thursday, with a series of shortwaves rotating anticlockwise around the main parent low. These will provide the focus for more enhanced convection / showers, which may merge to give some longer spells of rain (a mix of dynamic and convective rainfall). One such feature will be affecting SW England during the morning, swinging eastwards across central/southern Britain to clear the east coast by evening. Either side of this, sunshine and diurnal heating will aid the development of numerous scattered showers, with a window of lighter surface winds and a greater potential for some low-level convergence/confluence to become established during the afternoon hours across the Midlands towards eastern England - this may aid development of deep convection.

Given 300-700 J/kg CAPE, steep mid-level lapse rates and some marginal shear, a few sporadic lightning strikes are possible. Hail up to 1.5cm in diameter will be possible from the most organised/intense cells. Showers will likely persist well into the evening and night given the proximity of the upper low, but will generally weaken in intensity as daytime heating subsides - the greatest risk of lightning overnight (20%) will probably be over the English Channel.

However, the overall setup is rather messy with fairly moist profiles and there may be quite a bit of cloud at times, especially as an occlusion drifts eastwards during the day, and this casts some doubt over how much/widespread lightning activity will be - it seems unlikely to be as significant as was the case on Easter Sunday, for example. Nonetheless, somewhat reluctantly issued a low-end SLGT (30%) for parts of England.

Convective Weather

WWW.CONVECTIVEWEATHER.CO.UK

---

Forecasting thunderstorms and severe convective weather across the British Isles and Ireland for up to the next 5 days.

 

[Thunder and Lightning]

Really looks like a squall is trying to form...

[Thunder and Lightning]

I'm not sure but I think that these showers have some association with the occluded front. The MetO surface charts are showing the occluded front oriented N to S across England. The storm motion is moving roughly NE so the storm motion is sort of parralel to the front, so I think a linear mode is definitely quite possible. Correct me if I'm wrong.

[Eagle Eye]

sounds right

[Thunder and Lightning]

Does anyone have an idea about the kind of shear we will be seeing today? There is about 40-50kts of 850mb winds so I was thinking there may be at least some.

[Eagle Eye]

It's still early in the morning this looks like the line of storms could last a while.

[Eagle Eye]

I reckon some quick but quite fast winds before the storms.

[Flash bang flash bang etc]

11 minutes ago, Thunder and Lightning said:

Does anyone have an idea about the kind of shear we will be seeing today? There is about 40-50kts of 850mb winds so I was thinking there may be at least some.

Supposedly marginal shear today.

I was wondering: when convergence is a trigger does this generally mean there’s likely to be less shear available, as the air is being forced upward rather than across?

[Thunder and Lightning]

The line looks to have intensified a bit, with what looks to be some embedded line convection. I'm guessing it moved into slightly more favourable environment. 

[mike5900]

Had some loud rumbles of thunder at 7.30am. 

[StormLoser]

Nice to step out and see active bubbly cumulus, a ton of moisture in the air and loads of higher clouds. Looking good!  Estofex and Dan seem to agree.

But I think here in the SE we're in more for fast moving heavy showers than anything seriously thundery. I think we need more heat on the ground but the sun isn't really getting to work.

[Thunder and Lightning]

2 minutes ago, StormLoser said:

Nice to step out and see active bubbly cumulus, a ton of moisture in the air and loads of higher clouds. Looking good!  Estofex and Dan seem to agree.

But I think here in the SE we're in more for fast moving heavy showers than anything seriously thundery. I think we need more heat on the ground but the sun isn't really getting to work.

Just checked Estofex and saw they mentioned a strongly sheared environment for the England discussion... Not sure what to make of this? I though today was marginally sheared...

[Zak M]

Hoping for it here to go bang today.

[Ben Sainsbury]

21 minutes ago, Thunder and Lightning said:

Just checked Estofex and saw they mentioned a strongly sheared environment for the England discussion... Not sure what to make of this? I though today was marginally sheared...

Definitely aimed at much of France and Germany, they're expecting some enormous DLS values today >60knts.

Edited April 30, 2020 by Ben Sainsbury