Convective/Storm Discussion Thread - 19th May 2018 onwards

[West Sussex Kate]

Just seen the bbc weather wow!! Tomorrow sounds interesting, 

[TJS1998Tom]

15 minutes ago, Norfolk Sheep said:

Apart from the far East 

Typical storm shield for us, could get some elevated stuff maybe

[MattTarrant]

 

Day 2 Convective Outlook

VALID 06:00 UTC Thu 31 May 2018 - 05:59 UTC Fri 01 Jun 2018

ISSUED 21:17 UTC Wed 30 May 2018

ISSUED BY: Chris

A widespread thunderstorm outbreak is expected across southern Britain on Thursday. 

 

Mid-level instability will spread into southern England during the morning sparking the potential for thunderstorms by mid-morning across parts of Kent, Sussex and areas south of London. As the day progresses thunderstorms will develop more widely across southern England and eventually into Wales, the Midlands and parts of East Anglia. 

 

These storms will experience several different forcing factors. The aforementioned mid-level instability will spread further northwards into the Midlands, but should mix with surface based instability into the afternoon in response to daytime heating. CAPE values >1000 J/kg are forecast quite widely through the MDT and much of the SLGT area with PWATs in the low 30s mm. Both low-level and deep-layer shear will be weak, meaning storm modes will be messy, and largely pulse variety. Development of thunderstorms will likely occur in response to weak surface convergence, that is noted in the surface wind fields in the model, particularly from London across Bucks, Oxfordshire and Glocs. 

 

Weak steering flow will mean that thunderstorms likely sit over the same locations for an extended time, leading to the risk localised flooding. Some areas could receive in excess of 50mm of rain in less than 1 hour. The larger thunderstorm updrafts may also be capable of supporting hail to 2.5cm. 

 

Some uncertainty over MDT risk area as extensive low-level cloud during the morning could limit temperatures into the afternoon, and lead to lower CAPE values than the models are suggesting. 

 

A few isolated thunderstorms are possible in northwestern Scotland as well, with CAPE values over 700 J/kg forecast, however dry-midlevel conditions and capping at around 750mb will limit potential there. 

 

*Similar in nature to my forecast

[TJS1998Tom]

@MattTarrant What are your thoughts on the Lincoln area getting these storms tomorrow or perhaps the chance for anything elevated?

[Flash bang flash bang etc]

7 minutes ago, TJS1998Tom said:

@MattTarrant What are your thoughts on the Lincoln area getting these storms tomorrow or perhaps the chance for anything elevated?

That’s kind of the 1,000,000,000 dollar question...

The CW forecast Matt posted is clear that uncertainty remains on exactly where the storms will be and where they will be most intense.

You’re dancing near the edge of a ‘slight’ zone, so chances are fairly good you’ll get some sort of a storm fix in the afternoon.

Check the forecast maps - they make it fairly clear what they think (but remember it’s just a guide!)

Edit: sorry I didn’t mean to be his spokesperson oops

Edited May 30, 2018 by Flash bang flash bang etc

[Tom dewey likes thunder]

How often do UK get a supercell thunderStroms with very big hail stones

Edited May 30, 2018 by Tom dewey likes thunder

[Ben Sainsbury]

Tomorrow is looking to be a really interesting day in regards to organised and severe (possibly) storm activity. I will not be producing a storm risk map but I'll still identify to places at highest risk.

If we look at the charts, CAPE levels look in and around 1000J/kg which to clarify will be reached if we receive sufficient surface heating, stubborn cloud cover will significantly reduce these amounts. The interesting area for me is the introduction of basic levels of DLS, we're looking at 30kts over parts of CS England into West London. Here we could see more organised convection with updrafts having the ability to sustain themselves and as a result we could see some very prolific lightning given steep lapse rates too. Also as updrafts will be sustained through the basic levels of DLS we could see one or two isolated cases of large hail. There is a small possibility of these storms of CS/SE England could exhibit supercellular characteristics for a time where we see best overlap of convergence, DLS and CAPE. Areas further west will also see some active thunderstorms although less severe as a whole.

 

 

Edited May 30, 2018 by Ben Sainsbury

[alexisj9]

3 minutes ago, Tom dewey likes thunder said:

How often do UK get a supercell thunderStroms with very big hail stones

Not often, think recently about once a year roughly, and the hailstones are no where near as big as us one's.

[Norfolk Sheep]

Very doubtful about the outcome tomorrow - MetO says rain (a 50% chance in the afternoon) and NW has 0% storm risk. Ah well, it's still not quite June yet, maybe the east will grab all the action over the traditional months......

[Flash bang flash bang etc]

4 minutes ago, Norfolk Sheep said:

Very doubtful about the outcome tomorrow - MetO says rain (a 50% chance in the afternoon) and NW has 0% storm risk. Ah well, it's still not quite June yet, maybe the east will grab all the action over the traditional months......

Surely you’re not that far out of the action zone?

[MattTarrant]

@TJS1998Tom

It is difficult to pin point the exact likelihood of Lincoln receiving a thunderstorm, though I would argue under current model guidance that an elevated batch of storms may progress far enough north to produce some sporadic lightning (Early Afternoon). It is important though to stress that a weakening trend will exist! A very isolated surface based storm could develop (Late Afternoon) also, though this considered a low to very low threat  . Please use this only as a guide!

[Frosty hollows]

Think I could be in the right place at the right time tomorrow.  Best make sure I have phone, camera etc ready. Of course I could equally be 20 miles out and see naff all!

[SenlacJack]

1 hour ago, Flash bang flash bang etc said:

For the south coast are we supposedly seeing something during the wee hours?

I saw a forecast earlier which mentioned thunderstorms for parts of Surrey at 12am - but that’s in two hours

I always thought 12am was Midday, not Midnight ?

[ChezWeather]

All the action forecast for the South again!? 

We're doomed! 

[Cambridgeshire Weather]

1 hour ago, Flash bang flash bang etc said:

For the south coast are we supposedly seeing something during the wee hours?

I saw a forecast earlier which mentioned thunderstorms for parts of Surrey at 12am - but that’s in two hours

12 at midnight?? I think that's way to early

[Flash bang flash bang etc]

27 minutes ago, SenlacJack said:

I always thought 12am was Midday, not Midnight ?

I’m pretty sure 12pm is midday.

But - to clarify - I meant midnight

[Cambridgeshire Weather]

31 minutes ago, MattTarrant said:

@TJS1998Tom

It is difficult to pin point the exact likelihood of Lincoln receiving a thunderstorm, though I would argue under current model guidance that an elevated batch of storms may progress far enough north to produce some sporadic lightning (Early Afternoon). It is important though to stress that a weakening trend will exist! A very isolated surface based storm could develop (Late Afternoon) also, though this considered a low to very low threat  . Please use this only as a guide!

Very accurate statement. There would definitely be an elevated batch of storms progressing north however,  scattered missing out various areas so Lincoln definitely in threat of being in the firing zone as well as all the other cities.

[Flash bang flash bang etc]

3 minutes ago, Neglectedchicken said:

12 at midnight?? I think that's way to early

That what I read - think it was accuweather so it may as well have been tea leaves, but I guess it’s still vaguely possible

[Cambridgeshire Weather]

6 minutes ago, Flash bang flash bang etc said:

That what I read - think it was accuweather so it may as well have been tea leaves, but I guess it’s still vaguely possible

I honestly don't think its possible. Maybe 7am?

[Allseasons-Si]

Estofex latest,it's not a level 2 but i would take a level 1 over nothing

Storm Forecast
Valid: Thu 31 May 2018 06:00 to Fri 01 Jun 2018 06:00 UTC
Issued: Wed 30 May 2018 22:10
Forecaster: GATZEN

A level 2 was issued across north-eastern France into southern Germany and parts of Switzerland and Austria for excessive precipitation and to a lesser extent large or very large hail and severe wind gusts.

A level 1 was issued across the southern British Isles, Benelux, most of Germany, Czech Republic, northern and western Balkans, and Italy mainly for excessive precipitation.

SYNOPSIS

An ill-defined mid-level omega controls the mid-level flow. Troughs are centred west of the Bay of Biscay and over Turkey. Downstream of the omega ridge across southern Scandinavia, an intense trough amplifies into south-western Russia. Whereas arctic air masses advect into Russia in the wake of this trough, warm air remains over large portions of Europe. This warm air is associated with rich low-level moisture and steep mid-level lapse rates, resulting in CAPE of 1000-2000 J/kg in the afternoon. Widespread storms are forecast within the warm air. Large-scale lift will support initiation from the southern British Isles towards northern Italy due to an elongated vort-maximum slowly moving north-east. At low-levels, a convergence zone evolves below the mid-level vort-max that separates the warm air from cooler maritime air masses across western Europe.

DISCUSSION

North-eastern France into southern Germany and parts of Switzerland and Austria, northern Italy

Remnants of overnights storms will continue in parts of the forecast area in the morning and insolation is limited in some places. Areas with strong diurnal heating will experience CAPE of more than 1000 J/kg in the course of the day, together with high precipitable water. Vertical wind shear will be about 15 m/s in the lowest 6 km, supporting multicells and also a few supercells. Main threat is excessive precipitation and local flash flooding. Additionally, large or very large hail and severe wind gusts are possible with the stronger storms. With continuing large-scale lift, storms are expected to cluster and form mesoscale convective systems, travelling north or north-east from the late afternoon well into the night. Excessive precipitation and severe wind gusts will be the main threat after sunset.

Southern British Isles, Benelux, most of Germany, Czech Republic, northern and western Balkans, Italy

In a weakly-sheared but unstable environment, widespread storms are forecast during the day. Main threat is excessive precipitation and local flash floods, but stronger pulse storms can also produce large hail and severe wind gusts. Storms will gradually weaken after sunset.

http://www.estofex.org/

 

 

Edited May 30, 2018 by Allseasons-si

[Flash bang flash bang etc]

11 minutes ago, Neglectedchicken said:

I honestly don't think its possible. Maybe 7am?

It is possible.

 

There, said it

[Cambridgeshire Weather]

7 minutes ago, Flash bang flash bang etc said:

It is possible.

 

There, said it

keep dreaming

[Tom dewey likes thunder]

That bunch of thunderStroms out in the north sea from Denmark still going as I am watching it on real lighting maps

Edited May 30, 2018 by Tom dewey likes thunder

[alexisj9]

11 minutes ago, Flash bang flash bang etc said:

It is possible.

 

There, said it

If I start hearing rumbles, and seeing flashes in tonight's thick fog, I'll let you know.

[MattTarrant]

25 minutes ago, alexisj9 said:

If I start hearing rumbles, and seeing flashes in tonight's thick fog, I'll let you know.

Thunder Fog... Has a ring to it