Storms and Convective Discussion - 20th April 2019 onwards

[Zak M]

Had a very nice thunderstorm today with some good lightning and cracks of thunder.

https://www.youtube.com/watch?v=VJslzbjO-yM&t

[Arnie Pie]

Nice catch there Zak

.cracker @Another Kent clipper.....i fold

Edited May 2, 2019 by Arnie Pie

[Another Kent clipper]

1 hour ago, Arnie Pie said:

Nice catch there Zak

.cracker @Another Kent clipper.....i fold

It should be me folding, your cell is darker!

[Zak M]

Just when I thought a thunderstorm could do for the rest of the day, this beauty arrives 

 

[Azazel]

Rained here for a bit earlier.

[Jamie M]

The only real thing I had here was quite a heavy downpour that lasted for around 10 minutes.

[Arnie Pie]

15 hours ago, Another Kent clipper said:

It should be me folding, your cell is darker!

Your poker face is awsome though

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Sat 04 May 2019 - 05:59 UTC Sun 05 May 2019

ISSUED 19:11 UTC Fri 03 May 2019

ISSUED BY: Dan

Upper trough continues to drift southwards from the North Sea / Scandinavia across into mainland Europe. While the trough axis will have moved away from the British Isles, mid-level lapse rates will remain sufficiently steep, combined with marginal CAPE, to allow a few isolated lightning strikes from the most intense cells.

Showers will tend to decrease in intensity and coverage during the evening and night hours as daytime heating subsides and upper cold pool moves away.

http://www.convectiveweather.co.uk/forecast.php?date=2019-05-04

[Aiden2012]

Just had 2 bright flashes of lighting here in Bridlington, on the east coast. Moved away quickly but nice suprise. 

[Harry]

Started lovely and sunny here today, which will hopefully aid those lapse rates. Only down side is there is no CAPE, surface based or elevated to speak of. I think will be extremely lucky to get any thunder/lightning today

[Weather-history]

Some weak showers developed

 

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Mon 06 May 2019 - 05:59 UTC Tue 07 May 2019

ISSUED 07:18 UTC Mon 06 May 2019

ISSUED BY: Dan

Cold pool associated with an upper low over Scandinavia will give a glancing blow over the Northern Isles on Monday morning. Scattered showers may produce a few isolated lightning strikes given reasonably steep mid-level lapse rates and marginal CAPE, the risk reducing through the afternoon.

Elsewhere, an occluded front will slowly drift southwards from southern Scotland into Northern Ireland, northern England and East Anglia. The front is expected to become increasingly convective in nature, aided by low-level convergence and some diurnal heating. While CAPE is rather meagre, the environment is well-sheared which may be enough to compensate for an isolated lightning strike. That said, profiles remain capped at around 700mb, therefore limiting convective depth.

http://www.convectiveweather.co.uk/forecast.php?date=2019-05-06

[Summer Sun]

Day 3 Convective Outlook

VALID 06:00 UTC Wed 08 May 2019 - 05:59 UTC Thu 09 May 2019

ISSUED 15:44 UTC Mon 06 May 2019

ISSUED BY: Dan

An upper trough will slowly migrate eastwards across the British Isles on Wednesday, becoming rather elongated as the original low centre fills and a new one develops on its eastern flank. This creates a rather complex upper-level pattern with some uncertainty as to the exact shape / positioning / timing of various features crucial for the development of deep convection.

Nonetheless, a frontal system and associated precipitation will migrate northwards across the British Isles on Wednesday morning, with a clearance then developing across southern areas coinciding favourably with peak diurnal heating. With cold air aloft combined with surface heating, 300-600 J/kg CAPE is expected to develop in an environment with notably steep mid-level lapse rates. Scattered showers are likely to develop, especially inland where low-level convergence will be maximised (particularly peninsula convergence from SW England to East Anglia). A few thunderstorms will be possible, though this quite dependent on the upper pattern which ultimately dictates how favourable the overall environment may be. Some hail is likely in the most intense cells.

There may be scope to introduce a low-end SLGT over parts of the Midlands / East Anglia, but given the uncertainty confidence is not particularly high at this early stage. Any showers/storms that do develop will weaken during the second half of the evening as nocturnal cooling of the boundary layer commences. There may also be some longer spells of showery rain moving across the English Channel into southern coastal counties during Wednesday evening, though the exact track of this small-scale feature is uncertain.

http://www.convectiveweather.co.uk/forecast.php?date=2019-05-08

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Tue 07 May 2019 - 05:59 UTC Wed 08 May 2019

ISSUED 16:21 UTC Mon 06 May 2019

ISSUED BY: Dan

There is likely to be very little lightning through this forecast period.

A broad westerly flow covers the British Isles on Tuesday, under an upper ridge. However, low-levels remain reasonably moist courtesy of the remnants of a decaying frontal boundary, which combined with diurnal heating and low-level convergence will encourage convective development during Tuesday daytime.

Numerous showers will develop almost anywhere from the M4 northwards, though with weak instability and capping at 600mb lightning is rather unlikely. Hence for most areas, the risk of lightning is considered very low / around 5%. However, a relatively slack surface pattern may promote the development of a few funnel clouds. Any showers that do develop will tend to decay during the evening hours as daytime heating subsides.

On Tuesday night, frontal rain will spread north across most parts of the British Isles, as an area of low pressure approaches from the Atlantic. During the early hours, much stronger forcing aloft, combined with increasingly steep mid-level lapse rates (as cold pool aloft approaches) and a few hundred J/kg CAPE may result in some embedded convective elements on the rear side of the cold front - and hence it is this, and the post-frontal environment, that is more conducive to producing lightning during this forecast period. Main area of interest is SW England, Cen S England, S Wales, Celtic Sea and perhaps the extreme south of the Republic of Ireland.

http://www.convectiveweather.co.uk/forecast.php?date=2019-05-07

[Weather-history]

 

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Wed 08 May 2019 - 05:59 UTC Thu 09 May 2019

ISSUED 19:51 UTC Tue 07 May 2019

ISSUED BY: Dan

An upper trough will slowly migrate eastwards across the British Isles on Wednesday, becoming rather elongated as the original low centre fills and a new one develops on its eastern flank. This creates a rather complex upper pattern, with some uncertainty as to the exact shape / positioning / timing of various features crucial for the development of deep convection. 

Excessive cloud cover may inhibit thunderstorm potential somewhat, and will need monitoring.

Frontal rain will migrate northwards across the British Isles on Wednesday morning, with a clearance then developing across southern areas coinciding with peak daytime heating. Cold air aloft combined with surface heating will generate 300-600 J/kg CAPE within an environment with notably steep mid-level lapse rates. Scattered showers are expected to develop, initially over southern England on Wednesday morning, the risk then extending northeastwards across parts of the Midlands and East Anglia into the afternoon. A few thunderstorms will be possible, particularly focussed where low-level convergence is maximised (especially in a zone from SW England across the M4 towards East Anglia, bounded by the SLGT area). Shear is somewhat limited given similar wind speeds / direction through depth. Hail up to 1.5cm in diameter is possible from the most intense cells.

Some uncertainty exists over the potential for more cloud and showery outbreaks of rain that could develop over SW England during the afternoon hours, associated with an area of low pressure running eastwards nearby (over the western English Channel). NWP guidance differs in its handling of this feature, and if this cloud/rain does push into SW England (and further east later in the afternoon) then this may reduce the overall thunderstorm potential, especially in the southern portion of the SLGT. Meanwhile the far north of the SLGT area (i.e. Lincolnshire) is subject to slow cloud clearance following morning rain - some model guidance restricts instability to The Wash southwards.

Any showers/storms that do develop will tend to weaken during the second half of the evening as nocturnal cooling of the boundary layer commences - though some forcing from low-level convergence may persist along the axis of the elongated area of low pressure well into the night. 

http://www.convectiveweather.co.uk/forecast.php?date=2019-05-08

[BrickFielder]

 Looks like one of those days where forecasting is extremely tricky and I am not sure how much to trust the modelling. From Satellite images we can see the frontal system swinging up northward across the UK, but there is also evidence of a second front developing in what looks like a partial MCS. This is going to alter the times for cloud clearance and narrows the window of opportunity for thunderstorms to develop. Looking at the moment of the two centers of low pressure it looks like the weaker one to the west of the UK will slow down with the result that the deeper low to the south west of Ireland will not be pushed so far south and come closer to the UK.
 Generally speaking discreet thunderstorms require some sort of triggering mechanism whether that be cold air aloft, moist air at the surface,wind convergence, surface heating or orographic lift. I can see some wind convergence areas developing in very slack wind conditions. It is not clear however whether those convergence zones are modeled as a result of storm development or other conditions.
  Looking at the forecast skewT's we can see a very moist air profile all the way up which usually means rather messy convection. There is an area of increased low level wind speed shear towards the more south east and towards the east which could help storm inflow.
  Over all temperatures of 13 degrees in the sun do not generally indicate strong storms and I have doubts about some of the modelling. Assuming the modelling is mostly right then we should be watching East Anglia later this afternoon and perhaps the north midlands. My gut feeling is that post frontal convection is likely to be more limited to the south and perhaps south west generally with still a risk for East Anglia soon after frontal clearance. The modeled low level wind convergence bothers me in that it could indicate storms developing their own wind fields which makes severity of storms unpredictable.

[MP-R]

Some electrical activity in the SW. One cell just passing Wells, which I can see from North Somerset but has missed me to the southeast. Likewise, another batch over Devon/Cornwall, seemingly from convergence popping some strikes.

[ThundersnowDays]

First thunderstorm of the year here. About a dozen rumbles and some small hail.  The main core of the storm passed just south of me.

Edited May 8, 2019 by ThundersnowDays

[Super_Uwe]

Yes plenty of beefy showers rattling around Devon and Cornwall at the moment.

Lightning or not, wouldn't be surprised to hear of some localised flooding issues later on.

 

[Andy Bown]

3 minutes ago, ThundersnowDays said:

First thunderstorm of the year here. About a dozen rumbles and some small hail. 

Not so much activity 10 miles South of you but a heavy hailstorm and one very bright flash followed by shotgun thunder.

Edited May 8, 2019 by Andy Bown

[A.J]

thunder and lightning here.....nice!

[Jasper Foxx]

Thunder and lightning and very big raindrops on a storm just approaching Bristol. Sat on Bedminster down watching it roll in from north Somerset. Great little vantage point up here.

[Azazel]

Will today be the day? Sferics to the South East and North West.

[Jasper Foxx]

Make that hailstones now!