Storms and Convective discussion - November 2023 onwards

[Eagle Eye]

Great example of a cycling mini-squall line today. These occur with interactions between the cold pool strength and low-level shear strength. 

1) Tight squall line with weaker trailing stratiform behind it, loses shape as the stratiform region is stronger.

2) Development of cell into the system temporarily outbalances the cold pool and the frontal lobe of the mini-squall tightens. Except for where it disconnects further north with less momentum and shearing effects. 

3) Once the new cell cycles into the system, the cold pool re-strengthens and timilts the updrafts back for most of the frontal lobe of convection leading to a loss in the uniform linear mode. Squall line loses shape. 

4) As this loses energy, the stratiform region becomes the dominant force and it loses all shape. This is where the mini-squall is unlikely to reform properly till it re-encounters energy. 

[sunnijim]

UK weather warnings - Met Office

WWW.METOFFICE.GOV.UK

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Met Office UK weather warnings for rain, wind, snow, ice, fog, thunderstorm, lightning and extreme heat.

Could get lively tomorrow....

Thunder; hail and gusts of 70mph possible.

[sunnijim]

A TORRO watch too

The Tornado and Storm Research Organisation (TORRO)

WWW.TORRO.ORG.UK

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TORRO is a privately-supported research body specialising in severe convective weather in Britain and Ireland

 

[Nick F]

SEVERE WEATHER WATCH - THURS 22 FEB 2024

Issued: 21/02/2024 21z to 23/02/2022 00z

• Strong wind gusts up to 45-60mph
• Isolated tornadoes
• lightning
• Hail 
• Intense rain leading to flash-flooding

Areas at risk of the above: S IRELAND, SW ENGLAND, S WALES, S MIDS, S ENGLAND, E ANGLIA

An upper shortwave trough emanating from NE Canada will sharpen as it tracks east towards the British Isles at the base of deep upper low centred near Iceland. The shortwave trough will engage a cold front ahead of it during Thursday, as it catches up with it, causing a wave to develop and eventually a surface low along it across southern Britain during the morning.

Tonight, a cold front moving in across the far west this evening is already producing strong convection embedded within heavy rain along front, with quite active lightning activity noted across W Ireland and W Scotland. Broken band of heavy rain, with embedded convection will continue to move east across Ireland, N. Ireland, northern and western areas of mainland UK overnight, perhaps with isolated lightning toward western coastal areas.

A separate cold front to the south will develop a wave from the SW during Thursday morning, in response to the upper shortwave arriving and engaging from the west. So heavy convective pulses of rain are forecast to develop across SW England, Wales and into Midlands, likely organising into a squall line due to strong low-level jet stream and shortwave trough axis arriving parallel to cold front. The squall line crossing east over Midlands, S England and E Anglia. Strong convective gusts of 45-60mph may be produced by the squall line, along with intense rainfall leading to flash-flooding and perhaps hail. Also, should broken line segments develop in the squall line, there is an enhanced potential for a brief tornado in the gaps where winds back ahead of the squall.

Issued by: Nick Finnis

[Eagle Eye]

Convective Outlook️ 

A couple different linear modes appear likely to push through the south and eastern parts of the country but some models do push convection into the midlands and the north as well though. Most convection appears to be likely in the southern parts of the country.

 

An initial system should move through the country in the morning moving NE. Hitting the SW between about 4-8am then moving NE fairly slowly till it hits east Anglia and maybe the SE around 11am maybe delayed till mid day. This could also extend further north into the midlands and the north depending on the size of the PV lobe. Fairly good initial 3CAPE and low-level shearing may favour some tornadic potential but there's still a lot of differences in modelling. Whilst not particularly strong lapse-rates and weak MLCAPE, there may be favourable kinematics for longer lived storm cells and parcels parallel to the flow for 7km cloud heights. The strong buoyant airflow in the SE around mid day near the surface with negative lifted index between the surface and 850s staying strong for most of the SE. Lightning should mostly stay sporadic but for the time of year it's quite a strong system. 

 

Given potential cell clustering and momentum exchanges, near severe hail and tornadic potential with turbulent surface flow are possible. The cell clustering is because the next system follows close behind or is part of the main system and clusters up in the eastern part of the country. Eventually showers should start scattering in the afternoon and clearing later on, most of the potential is held in the south and the east mid day, then in the morning further west and there's more mixed signals.

Alongside that, wind gusts are likely to be strong because this all happens with a low moving through for the south mainly. Potentially severe wind gusts for coasts and slightly inland. 

There is potential for a squall line to form if vorticity is strong enough, if that does happen than severe wind gusts inland are also very possible. There's a lot of mixed signals on whether there's merging of systems or whether they disconnect or don't disconnect so it's hard to tell whether a squall line will form. 

In western Scotland there's a rash of heavy showers likely along rolls of vorticity. Potentially a more favourable area for lightning than the southern mode because of more widespread 50+ J/KG of 3CAPE but less likely to have severe threats associated.

Edited February 21 by Eagle Eye

[Daniel_c150311]

Just woke up to heavy rain and strong winds, looked at the radar and I’m on the small line right now.

[Thunders]

It’s annoying this is gonna hit us whilst I’m  at school.  At least  this is early season so shouldn’t be too extreme and I won’t miss out on too much. 

[Thunderspotter]

I should be at school, but they've decided to close until 10:45 this morning after a fatal crash on the M27 westbound - Very sad and traffic is chaotic.

This however means I'll be able to track this squall for a little bit. I don't think the heavy parts are going to hit my area until about 13:00. Sadly I'll actually be in school at that time.

[Ryan H]

Now I had looked on the Meteologix.com Website to see if there is any sign of lighting from the weather front and there is some dark blue bits in areas like London for example. No Lighting as shown in Yellow however.

 

[Eagle Eye]

Fun examples of a leading stratiform region from the cold front driven first squall ahead/in line with the low/developing low to it's north tilted SE. 

Whereas the NE tilted system with a leading stratiform region from a trough behind the low's centre. 

Leading stratiform region - Winds flowing back to front. 

Trailing stratiform region - Winds flowing from front to back. 

With the pulling towards a low pressure it makes total sense. 

Let's talk cell motions as well. 

Following the shearing direction. The majority of the low-level shear should contribute to NE movement, whereas cell motion from a lot of what I see appears to follow the upshearing direction which is SE. 

Hence the bottom cell moves SE whereas the system moves NE. Also watch how the cell just to the south of the one I highlighted also moves SE. 

Storm movement is still NE here with the shearing direction NE but cell motion should also be NE as the upshear is slightly NE of surface shear. 

There we go, yes they're all moving NE. There's still replacement cycles though and especially away from France as we've seem it can easily get messier over the channel. 

[Eagle Eye]

Pre-multi clustered storm thingy. 

[LightningLover]

Look at how the storms have exploded in the Southern North Sea!

[Retron]

A fascinating - and rare - experience here, as near calm winds were replaced in just a few minutes with strong, gusty ones.

There are two attachments here - the first is the wind gust graph from the yacht club in Sheerness, the other is the radar from the same time as the winds really picked up - I was expecting fireworks from that more intense line to the west, but was from the relatively innocuous one further east.

It's certainly novel, anyway!

[Daniel_c150311]

I think I have some convection in south Wales as the clouds seem to be bubbling up nicely

 

   

[Metwatch]

Interesting skies as the front was clearing in the last half hour.

[Daniel_c150311]

 this is a video of developing Cumulonimbus/ high cumulus

[Eagle Eye]

Can't confirm it but think that's the first lightning of the season seen for me, big distant flash whilst I was lying in bed and looked out and saw some CB's also lightning has shown up in the channel recently.

[Eagle Eye]

Another day, another set of circumstances for me missing lighting. First off, first mini-distant storm, had to charge my camera. Second mini-distant storm set camera to 20 second exposures automatically for a burst, 2 seconds after the burst finishes, lightning strikes, a CG, that I saw on my camera as it was on but it had just stopped filming and if there would've been 1 more picture to the burst I would've got the lightning.

[Metwatch]

Colder unstable polar maritime air is fully with us, bringing in a lot of showers. A shower passing north of here in the last half hour.

 

Also saw this cool capture from Cornwall yesterday evening, thought I'd share here. I imagine a fair amount of hail is falling from them as well. 

Edited February 23 by Metwatch

[Robert1981]

 Metwatch the picture from Cornwall i saw this morning near Boston Lincolnshire the wash area it looked great also nice pictures. 

[Sprites]

On the squall line yesterday

https://www.swindonadvertiser.co.uk/news/24137385.bins-sent-flying-swindon-street-mini-tornado/

 

[Andy Bown]

 Sprites

Mini tornado

[Azazel]

Pea sized hail in Andover 

[amybonnie98]

Hail in Southampton and towers building

[Daniel_c150311]

think this might be another cumulonimbus cloud but it could be nimbostratus, the clouds are still towering very tall since yesterday.