Convective / Storm Discussion Thread - 31st May 2017 onwards

[Had Worse]

Odd?

 

www.metoffice.co.uk  gets Hmmm cant reach this page. ( Cue twilight zone theme)

[East_England_Stormchaser91]

2 minutes ago, cheese said:

18C here with that dreaded North Sea low cloud making a comeback. If the max temperature doesn't exceed 20C then today will be more than 10C cooler than yesterday (30C). You guys are welcome to this rubbish!

Tomorrow looks better, thankfully.

Always turns up and impedes the view of a storm too does North Sea crud. It's been a massive nuisance at times in the past for myself and many who live in the east. Holbeach is showing 18c with a dew point also of 18c! So I guess that'll be why some crud is readily forming. Always happens when the DP's skyrocket. 

[TJS1998Tom]

Just checked the forecast for tomorrow night, if it goes ahead then us in Lincolnshire will be up for a treat

Looks like I'll be having a late night lol

[Pat Butcher]

3 minutes ago, Had Worse said:

Odd?

 

www.metoffice.co.uk  gets Hmmm cant reach this page. ( Cue twilight zone theme)

It's .gov.uk

[Hodgheg]

41 minutes ago, Davethedog said:

Interesting feature on the SRH charts on lightningmaps..

This seems to becoming a theme today. 

On the topic of people getting over excited at the risk of supercells and tornadoes. These words are rarely used in mainstream forecasts. When online sites talk, sometimes correctly about the risk, people have a tendency to believe this must be something different and special, even though these risks were always there in past events. It's a trap I've found myself in before and even now I find it too easy to get excited. 

[Nick L]

Just now, John Hodgson said:

This seems to becoming a theme today. 

On the topic of people getting over excited at the risk of supercells and tornadoes. These words are rarely used in mainstream forecasts. When online sites talk, sometimes correctly about the risk, people have a tendency to believe this must be something different and special, even though these risks were always there in past events. It's a trap I've found myself in before and even now I find it too easy to get excited. 

Yep, supercells are not some incredibly rare thing for the UK. They're unusual but they do happen. I have never seen the Met Office mention the word, however.

The problem is that they are very difficult to identify with the radar data available. Unfortunately, the Met Office don't make the necessary radar data publicly available (even to buy) unlike the freely available data in the states.

Edited June 20, 2017 by Nick L

[Mapantz]

7 minutes ago, Davethedog said:

It's .gov.uk

www.metoffice.co.uk works as well, as it is a redirect.

[TJS1998Tom]

2 minutes ago, Nick L said:

Yep, supercells are not some incredibly rare thing for the UK. They're unusual but they do happen. I have never seen the Met Office mention the word, however.

The problem is that they are very difficult to identify with the radar data available. Unfortunately, the Met Office don't make the necessary radar data publicly available (even to buy) unlike the freely available data in the states.

If you were to take a rough guess by looking at the recent charts of high cape, if Lincolnshire got any storms tomorrow night; how many lightning strikes a minute could we potentially be looking at?

[Hodgheg]

Just now, Nick L said:

Yep, supercells are not some incredibly rare thing for the UK. They're unusual but they do happen. I have never seen the Met Office mention the word, however.

I'd imagine they don't use the word to avoid panic. The risk from panic outweighs the benefits of using the words. It's not like in the US where people are more educated on those terms, and where the risk of occurrence is higher. 

It migh be my imagination but I'm sure I've seen the word tornado used in the forecasters assessment part of a warning a few years ago. 

[Nick L]

2 minutes ago, John Hodgson said:

I'd imagine they don't use the word to avoid panic. The risk from panic outweighs the benefits of using the words. It's not like in the US where people are more educated on those terms, and where the risk of occurrence is higher. 

It migh be my imagination but I'm sure I've seen the word tornado used in the forecasters assessment part of a warning a few years ago. 

That's another reason too. The vast majority of the UK public would have no idea what a supercell is.

I've not seen it myself, I've seen them mention large hail before though.

Edited June 20, 2017 by Nick L

[Methuselah]

Just now, Nick L said:

That's another reason too. The vast majority of the UK public would have no idea what a supercell is.

I've not seen it myself, I've seen them mention large hail before though.

Most'll likely think it's a super-efficient battery?

[Had Worse]

14 minutes ago, Davethedog said:

It's .gov.uk

Yeah, my typo on the forum, still wont work... baffled

 

[Another Kent clipper]

11 minutes ago, John Hodgson said:

This seems to becoming a theme today. 

On the topic of people getting over excited at the risk of supercells and tornadoes. These words are rarely used in mainstream forecasts. When online sites talk, sometimes correctly about the risk, people have a tendency to believe this must be something different and special, even though these risks were always there in past events. It's a trap I've found myself in before and even now I find it too easy to get excited. 

Sorry, supercells and tornadoes what? I didn't catch the rest

[80sWeather]

6 minutes ago, Ed Stone said:

Most'll likely think it's a super-efficient battery?

And there was me thinking it was a extra  large prison.....

[TJS1998Tom]

Latest BBC forecast says gusty winds, torrential rain and hefty hail for tomorrow night quite widely 

[Dami]

BBC says there are yellow warnings for Bedford but MetO tells me there are none. I am just on the edge of the warning box so you dunno, stranger things have happened.

[Had Worse]

I'm smack in the middle of the yellow area but that doesn't mean i'll get anything.

 

I expect the met will issue amber flash warnings close to or during the fun & games (disclaimer - not so if your house is flooded or you suffer a lightning strike).

[Mapantz]

1 minute ago, Had Worse said:

I expect the met will issue amber flash warnings close to or during the fun & games

Very unlikely.

The warning matrix is in the 'unlikely' category.

[Nick L]

I know most are aware of this but to avoid the usual toy throwing from a minority, being in a warning area does not guarantee you are going to see storms. You could personally see nothing, but the warning is spot on because some places did.

[Ben Sainsbury]

Some decent sized cumulus around, positive sign right now and hope the cap can be broken later! 

[Flash bang flash bang etc]

I think if any storms are to be had today it's gonna be this area which is best suited to producing them - and the direction of likely travel of any that do get off the ground:

Its frustrating me how any potential this week seems to consistently be in the north. I'm not joking when I say that Surrey and the counties around it have been chronically outside of storm risk zones so far this year - and we were in storm deficit to start with so lagging behind by a considerable margin now.

I'm speaking generally here - I know we've had a rumble or two but it's just not producing like the rest of the country and I would have thought with the intense humidity and heat this week it's a no-brained that some of the most intense storms would be in or around this area.

Even if they were close enough for a 1 hr drive or so I wouldn't mind too much but anywhere north of Oxford is too far for mid-week chasing

Edited June 20, 2017 by Flash bang flash bang etc

[StormChaseUK]

The convergence zone around Brecon/Hereford/Glouc zone about 5pm looks to be the area that might spark off showers.

[Nick F]

Storm & Convective Forecast

Issued 2017-06-20 12:03:56
Valid: 20/06/17 12z to 22/06/17 06z

DAYS 1 & 2 CONVECTIVE / STORM FORECAST - TUES 20TH & WEDS 21ST JUNE

Synopsis

An upper high which has persisted over southern Britain over recent days will begin to weaken and retreat SE during the rest of this week, as an upper trough approaches and moves in across western Britain by early Thursday. A surface high will drift east across northern Britain on Tuesday, pushing a weakening boundary southwards across England and Wales, separating hot and humid air to the south and cooler and fresher conditions to the north currently over Scotland. Surface convergence to the south of this boundary moving south may, with heating, trigger a few isolated afternoon storms. The same boundary will stall late Tuesday before drifting north as a warm front across northern Britain Tuesday night and through Wednesday, warm and humid plume returning north across below this warm front will likely destabilise across northern Britain early Wednesday, then further south later in the day.

DAY 1 CONVECTIVE FORECAST

Valid: Tuesday 12z to Wednesday 06z

… WALES, MIDLANDS …

Although forecast isolated storm development failed to materialise over last few days across England and Wales due to stout cap caused by upper high and warm/dry profiles, continued weakening of heights and slight cooling aloft from the NW in tandem with surface breeze convergence just to the south of boundary shifting south and stalling may breach the stout cap to allow a few isolated thunderstorms. Should a storm develop, it will tap into a reservoir of hot and humid air with CAPE values forecast in the order of 1000-1500 j/kg CAPE. High rainfall totals in a short-space of time leading to localised flooding with be the main threat from any storm that does develop, given high PWAT (Precipitable Water) values of 30-36mm pooling along convergence zones. High CAPE may also support sufficient buoyancy for isolated large hail too, though limited by lack of any appreciable vertical shear. Despite favourable parameters for storms, there are doubts that upper ridging will weaken enough to allow storms to develop, like last few days, so have refrained from severe probabilities for now.

… N. IRELAND, N ENGLAND and S SCOTLAND …

A shortwave trough moving NE on forward side of long wave trough approaching Ireland will likely cause large scale ascent of warm/moist conveyor returning north across the UK/EIRE Tuesday night, leading to an increase in mid-level convection and eventually the development of elevated thunderstorms by 06z Wednesday 30-50 knot SWly flow at 500mb and 30-40 knot 0-6km effective shear will support storm organisation into clusters, capable of isolated large hail, high rainfall totals leading to localised flooding, gusty winds and frequent cloud-to-ground lightning. Have issues a MARGINAL risk for severe weather across N England and Scotland.

DAY 2 CONVECTIVE FORECAST

Valid: Wednesday 06z to Thursday  06z 

… N IRELAND, far N of ENGLAND and SCOTLAND …

Elevated thunderstorms are likely to be ongoing across N. Ireland, N England and Scotland during the morning with further storms perhaps developing through the day and moving NE, though they will be hit and miss in nature. Like the day 1 forecast, storms will be capable of hail, gusty winds and frequent lightning, though high rainfall totals leading to localised flooding will be main threat. Have carried over MARGINAL risk of severe weather before storms eventually clear east into the N Sea Wednesday evening.

… N ENGLAND, MIDLANDS and E ENGLAND …

Some elevated thunderstorms may be ongoing in the morning across the far north of England in association with destabilisation of warm moist plume returning north and destabilising across northern Britain as per forecast above, this activity clearing by afternoon. GFS and ECM forecast a highly unstable hot and humid airmass in place across much of England and Wales on Wednesday afternoon, with CAPE values in the order of 1000-2500 j/kg. Again, there is uncertainty whether the strong cap created by upper high across the south and EML (Elevated Mixed Layer) aloft will weaken, however with temperatures reaching 33C inland across central England, weakening heights and strengthening divergent winds aloft, along with weak surface trough moving east across central and northern UK creating convergence coupled with orographic lift, there may be sufficient forcing to break the cap to allow a few thunderstorms to develop across the southern Pennines, Midlands and parts of E England. Strengthening 500mb SWly flow aloft reaching 40-50 knots along with 30-40 knots of effective 0-6km shear suggests any storms that develop will quickly organise … with scope for a supercell or two … capable of producing large hail (1-2 inches), damaging wind gusts, flash flooding and frequent cloud-to-ground lightning. Also, likely discrete nature of storms and forecast strong storm-relative helicity may favour the development of tornado. However, given uncertainties of convective initiation in this region and isolated nature if storms do develop, have refrained from issuing more than a SLIGHT risk of severe weather for now, but may upgrade with the DAY 1 outlook update, if initiation looks more probable and widespread in one area.

... WALES and SW ENGLAND ... 

Later in the night until end of forecast at 06z Thurs, models indicate another round of thunderstorms, mostly elevated, forming along developing cold front shown on fax charts across Wales and SW England. These storms may bring a risk of torrential rain leading to flash-flooding.

Edited June 20, 2017 by Nick F

[Nick L]

4 minutes ago, StormChaseUK said:

The convergence zone around Brecon/Hereford/Glouc zone about 5pm looks to be the area that might spark off showers.

The Met Office UKV model is agreeing with that.

[Convective]

Satellite imagery showing a band of ACCAS over the Gloucestershire area. Maybe a good sign as the instability aloft begins to get some use.