Convective / Storm Discussion Thread - 31st May 2017 onwards

[poseidon]

Storms already kicking off in the Bay of Biscay.

[Ben Sainsbury]

5 minutes ago, poseidon said:

Storms already kicking off in the Bay of Biscay.

Just to note, GFS on track with where instability and precipitation might exist for the storms.

 

[Mapantz]

This is showing the convection as of 8:30pm

Edited July 4, 2017 by Mapantz

[Ben Sainsbury]

1 minute ago, Mapantz said:

This is showing the convection as of 8:30pm

And as always an Infrared Satellite Timelapse for those wondering here: http://en.sat24.com/en

Looking promising given the large CAPE levels in the area. To view a range of parameters for storms a good website here: http://www.lightningwizard.com/maps/

 

 

[Derecho]

With the air source coming from the Bay of Biscay I wonder what the chances are of some more thunder and lightning on Thursday evening down here? It looks as though the storms will affect the South early on in the day and move North if the forecasts are anything to go by. I can imagine there will be plenty of storms forming over France throughout the day though.

Edited July 4, 2017 by Quicksilver1989

[TJS1998Tom]

18z looking like it's pushing a storm from South West towards Lincolnshire for Thursday evening

[MP-R]

3 hours ago, Weather-history said:

http://old.wetterzentrale.de/topkarten/fsbeobl.html

Thanks!

2 hours ago, Supacell said:

To be honest I don't. There is the link that Weather History posted but to be honest I can't understand it as it is all in German

Yes I have that problem too. I can't find any option to put in dates.

[Flash bang flash bang etc]

Sounding good for some possibly overnight action tomorrow in the far south... I have two days without major plans and will nowcast with a view to action if it becomes favourable...

so exciting 

[sunnijim]

BBC forecast calling for an early start to storms on Thursday, the far South affected by 6am. By afternoon the focus has shifted North and East with the South drier in hot sunshine.Perhaps a second round overnight Thursday into Friday for the SE.

[Ben Sainsbury]

Increasing eastward shift on the latest GFS run too, very agonising but uncertain at this stage.

[LightningLover]

Morning! My exciment increases yet more, as storms are beginning to develop over The bay of Biscay. Perhaps I should try an all-nighter? 

[seb]

Can't remember the last time the MetO forecast mentioned the word severe!

SE forecast for tomorrow:

Thunderstorms will become more widespread and probably locally severe with hail and large amounts of rainfall.

Let's see what the updated warning later this morning says.

[Dangerous55019]

Morning all 
Time once again for my morning look at what the good ole 00z run from the GFS is forecasting...
Well, from a totally IMBY perspective, today has totally dropped off the radar, which to be honest, at such a close stage has come as a little bit of a surprise, but hey these things happen.
So all eyes on tomorrow... 
It is looking potentially really quite juicy. 
Lets just hope that the charts keep on improving for all of us 

[A.J]

1 hour ago, Ben Sainsbury said:

Increasing eastward shift on the latest GFS run too, very agonising but uncertain at this stage.

yes, and the in house NMM hi-res.......steering flow (T500 & T700 hpa winds) have too much of an easterly component as it stands taking elevated storms along the south coast and into the home counties/London, but the hi-res modelling does prog home grown surfaced based storms breaking out early afternoon over the West Country & BANES......still, i've only just woken up and am still on my first coffee so haven't had chance to peruse the other models 

[Chris K]

1 hour ago, Ben Sainsbury said:

Increasing eastward shift on the latest GFS run too, very agonising but uncertain at this stage.

Agree. The Netwx Sr model keeps the first opportunity of storms moving NE, sticking close to the S coast towards London during tomorrow daytime.

Then, a line of thundery showers break out early evening down the spine of England moving Eastwards. I wouldnt quite say the W country has no chance but the faster progression eastwards is appearing as we get closer 

The AROME model is further east yet again and I rate that model quite highly at the moment. Whilst I know models are only a guide and it comes down to watching radars on the day, my excitement has dwindled really.

Met office warning area still looking the like the main risk zone, but a movement east may occur.

Edited July 5, 2017 by Chris K

[Windblade]

I'm liking what I'm seeing so far. However, whats the bet the percentage will slowly decrease to zero over the course of the day?

[Frosty hollows]

I think we're going to get a soaking here, but am not expecting a storm (so will be pleasantly surprised if we do get one!)

[Weather-history]

14 hours ago, Weather-history said:

I'm waiting for Euro 4 to come within the critical time period. If that indicates something for my area then I will take more notice. Euro 4 didn't really go for much last time for this area.

Not looking good for here, things develop to my east. So I suspect a non event around here.

 

[I remember Atlantic 252]

13 minutes ago, Weather-history said:

Not looking good for here, things develop to my east. So I suspect a non event around here.

 

Non event here too, all going SE, then later in the day, spreading East, but north of here, bypassing here, pepping up for NE

This location as everyone knows is the lousiest in the UK, have not had even 1 flash/rumble yet this spring/summer

Edited July 5, 2017 by I remember Atlantic 252

[Another Kent clipper]

17 minutes ago, I remember Atlantic 252 said:

Non event here too, all going SE, then later in the day, spreading East, but north of here, bypassing here, pepping up for NE

This location as everyone knows is the lousiest in the UK, have not had even 1 flash/rumble yet this spring/summer

Historically I found nearby stoke where I used to live, quite good for storms, particularly the early nineties.  Of course I could be looking back through rose tinted spectacles.  Manchester has sucked since 2011 when I moved, save September 13th 2016

Edited July 5, 2017 by Another Kent clipper
Grammar

[Mapantz]

I was in Swanage around 7am, there were some quite big, convective drops of rain. It all vanished as I went to Poole.

[Weather-history]

5 minutes ago, Another Kent clipper said:

Historically I found nearby stoke where I used to live, quite good for storms, particularly the early nineties.  Of course I could be looking back through rose tinted spectacles.  Manchester has sucked since 2011 when I moved, save September 13th 2016

Started the year before in 2010, the 2010s have been really poor for thunder overall, just one or two highlights per year but thunder in general, it has been poor. eg  First thunder for 2015 wasn't until 1st July. 2013 has probably been the best year for thunder this decade.

[I remember Atlantic 252]

14 minutes ago, Another Kent clipper said:

Historically I found nearby stoke where I used to live, quite good for storms, particularly the early nineties.  Of course I could be looking back through rose tinted spectacles.  Manchester has sucked since 2011 when I moved, save September 13th 2016

Stafford generally sucked since '09, except for 11th May, good day for us @ajpoolshark

[Weather-history]

I am pretty sure it is rose coloured glasses but thundery prospects seem to be shunted further eastwards as zero hour approaches these days.

In the 90s, it happened as well but the shunting back westwards also happened

Take these three Rob McElwee forecasts, one  from 29th July 1994 and two for the following day

Note how the storms that developed are further back west and also the predictive temps in the SE increase in the second forecast

 

[Nick F]

Storm & Convective Forecast

Issued 2017-07-05 09:30:05
Valid: 05/07/17 06z to 08/07/17 06z

DAYS 1 & 2 CONVECTIVE / STORM FORECAST - 5TH/6TH JULY 2017

Synopsis

Trough disruption on the southern flank of the broad cyclonic upper Wly flow across the far N Atlantic leads to an upper low to drift S and SE across western Iberia over the next 36-48 hours. As a result, the upper flow across southern UK will back more towards a Sly from the generally Wly flow of recent days, allowing an unstable plume of warm and humid air over Biscay, W France and Iberia to spread N across S England by Thursday morning. A shallow surface low over the Bay of Biscay will expand north across S England with the plume spreading north, thunderstorms are likely to develop and move N within this plume across central, S and E England from Wednesday night through Thursday, some storms perhaps bringing severe weather. Some storms are also possible along a developing cold front moving in from the west across N Wales and N England on the NW edge of the plume.

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DAY 1 CONVECTIVE FORECAST – WEDNESDAY 5TH JULY 2017 (05/07 06z to 06/07 06z)

… S ENGLAND TONIGHT …

Plume of warm and humid air over France on Wednesday (with wet-bulb potential temps of 18-20C) will spread north into S England in the early hours of Thursday morning, an Elevated Mixed Layer (EML) aloft originating from the Spanish Plateau atop of the warm humid airmass will create steep lapse rates which, combined with isentropic lift on the northern edge of the plume helped by subtle surface trough moving NE over Biscay, will allow development of elevated thunderstorms over N France / English Channel areas tonight – which may move inland across southern counties of England by 6am (end of this day 1 forecast). Although deep layer shear will be weak (less than 30knts) combination of forecast MLCAPE values approaching / in excess of 1000 j/kg and strengthening SWly flow aloft will allow clusters of strong elevated storms to develop and move NE – bringing a risk of hail (isolated large), torrential rainfall leading to flash-flooding and frequent cloud-to-ground lightning. A MARGINAL risk has been issued for southern counties of England for overnight period.

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DAY 2 CONVECTIVE FORECAST – THURSDAY 6TH JULY (06/07 06z to 07/07 06z)

… S and CENTRAL ENGLAND, E ANGLIA …

Warm and humid air (WBPTs of 16-18C) will continue to advect N and NE across southern UK on Thursday in tandem with surface low drifting NE from NW France. A few clusters of elevated thunderstorms with isolated hail, torrential rain and frequent lightning maybe ongoing in the morning from the start of the forecast across parts of central-S and SE England, these will continue NE across SE England, Midlands and East Anglia, with potential for further storms, perhaps surface-based, to develop in wake of these early elevated storms into the afternoon across Midlands, SE England and E Anglia.

Model forecast skew-ts indicate that LCLs (Lifted Condensation Levels), which determine where cloud bases develop, will fall through Thursday, as surface airmass becomes increasingly moist. Also, the warm/dry nose/cap at around 850mb, which keeps convection elevated above it before then, is eroded as heights fall from the west with approach of an eastward-moving shortwave trough, so surface-based storms may develop into the afternoon as lift increases with approach of shortwave trough.

Airmass will be rather unstable across S England … Elevated Mixed Layer (EML) will create steep lapse rates atop of hot and humid surface airmass characterised by dew points in the high teens and precipitable water (PWAT) values of 33-36mm) … which is forecast to yield around 1000-1500 j/kg CAPE.

A shallow area of low pressure at the surface moving NE across SE England in the afternoon will create surface convergence which, combined with increasing large scale ascent of approaching shortwave, will create forced ascent of unstable surface airmass. As a result, organised surface-based thunderstorms may develop within an environment of increasing deep layer (0-6km) shear in the order 30-40knts … as increasing SWly flow aloft and backed winds towards the surface as upper shortwave approaches from the west. Clusters of storms, perhaps one or two with rotating updrafts / mesocyclones, may pose a risk of all severe hazards ... large hail (1-2 inches in diameter) and torrential rainfall leading to flash-flooding are the main threats – though for now any such threat should be considered isolated / SLIGHT risk. Also storms maybe accompanied by strong convective wind gusts and frequent cloud-to-ground lightning ... an isolated tornado cannot be ruled out, with any surface-based storm that forms along a wind convergence boundary - where storm-relative helicity will be maximised.

… E IRELAND, N WALES, N MIDLANDS, N ENGLAND …

A cold front developing over Ireland in the morning on the NW edge of the plume spreading into Sern UK will arrive across the above central areas of the UK in the afternoon. Lift by this front of warm/moist air to the SE of front is forecast to support the development of a band of heavy showers and thunderstorms across the above areas in the afternoon/early evening – before this activity clears east into the N Sea. Hail, flash-flooding, strong winds gust and frequent lightning may accompany these storms, so have issued a MARGINAL for these areas.

Issued by: Nick Finnis

http://www.netweather.tv/index.cgi?action=convective;sess=

Edited July 5, 2017 by Nick F