Storm & Convective Discussion - 04/07/15 Onward - Heat & Plumes

[Harry]

Having had another look at GFS, gradually pulling back the CAPE however intensifying it over France. MUCAPE levels meagre on GFS. Much better on NMM 5 (both 12z runs).

So, in short still the chance for a complete drop in potential, even very close to the event. Even on NMM 5 which is the more favourable chart currently, instability is a very glancing blow the SE corner (anywhere east of IoW and south of Norwich as a rough approximation)

[East_England_Stormchaser91]

Ah you see now 3rd/4th lacked thunder for me - immense amounts of lightning, but very little thunder, even from very close IC bolts (I.e right overhead).

Certainly close to the 48 hour window :That is stunning mate, well done! Enjoy every second of it and smash it! D

Was literally constant here. Numerous places in the fens got struck by lightning too. Quite an astonishing night. Was like watching one of those continental beasts that form over France into Belgium or Germany, except over us on that occasion! Edited July 14, 2015 by East_England_Stormchaser91

[Flash bang flash bang etc]

Hi everyone! I've taken a few days off watching the forecasts cos - let's be honest - unless you like the colour grey or getting very slightly wet the current conditions ain't gonna really interest anyone!

But reading recent posts imagine my joy... Especially as I'm free to chase Thursday eve!

Might even make a night of it and go for a pre-storm pub dinner :-D EXCITING!

Anyway I think I'm well placed for something - interestingly we were one of the few places which missed out on proper overhead storms the other week. maybe this will be our payoff?

[Harry]

Hi everyone! I've taken a few days off watching the forecasts cos - let's be honest - unless you like the colour grey or getting very slightly wet the current conditions ain't gonna really interest anyone!

But reading recent posts imagine my joy... Especially as I'm free to chase Thursday eve!

Might even make a night of it and go for a pre-storm pub dinner :-D EXCITING!

Anyway I think I'm well placed for something - interestingly we were one of the few places which missed out on proper overhead storms the other week. maybe this will be our payoff?

Excellent! Could be good timing that's for sure.

I would emphasise however that the models aren't quite as consistent as I'd like and I'm a little anxious as to whether the decent instability will actually arrive. GFS for example over the past few days has been gradually delaying the arrival of the warm/hot and humid air. On the latest BBC forecast for example they indicate the warm front down over SW France to start Thursday. But, while delaying the plume trends have been to slightly increase CAPE...the same can't be said unfortunately for MUCAPE which looks a lot more meagre compared with the NMM for example.

The timing of the Atlantic push against the creeping plume will be critical for our chances I feel. I am a lot less confident currently compared with two weeks ago. Furthermore to add a further fly to the stormy ointment, a bit of disparity as to where the focal point of any storms might be...BBC (and therefore UKMO I'm guessing) favouring C/S England (Beeb even showing lightning across Wales/NW which I am quite dubious of), little showing in the SE. NMM 5 by contrast tending to favour the SE whereas further west appears more frontal.

18z due out shortly.

[IanR]

Excellent! Could be good timing that's for sure.

 (Beeb even showing lightning across Wales/NW which I am quite dubious of), little showing in the SE. NMM 5 by contrast tending to favour the SE whereas further west appears more frontal.

18z due out shortly.

yes I am dubious too, after last fridays farce storm forecast for the north,    I know its hard to pinpoint where the storms will occur , but to claim ''thunderstorms are already marching northeastwards''  out of wales , when the rain band was not electrified in any way was just ridiculous thing to say

 

but lets leave that there,   

[Harry]

Early thoughts for Thursday from convective weather UK

Day 3 Convective Outlook

VALID 06:00 UTC Thu 16 Jul 2015 - 05:59 UTC Fri 17 Jul 2015

ISSUED 20:59 UTC Tue 14 Jul 2015

ISSUED BY: Dan

On Thursday, an Atlantic low will be located to the SW of Ireland, moving progressively due north. At the surface, a warm front will migrate northwards across the southern half of Britain, allowing poleward-advection of a very warm, moist low-level airmass across the aforementioned areas. The arrival of this high ThetaW air will be quite late in the day, as diurnal heating begins to subside, and will probably act as a cap to any potential surface-based convection given limited maximum temperatures in the upper 20s Celsius, despite increasing dewpoints through the evening hours. Consequently latest trends in the GFS, for example, are beginning to back away from producing sfc-based convection in the model world - not completely ruled out in the early evening hours at present, but an ever-declining trend.

Greatest attention is then turned to the potential for elevated thunderstorms to develop during the mid/late evening hours and thereafter, as the forward-side of the large-scale Atlantic upper trough, and an attendant shortwave, serve as the focus for convective initiation. Naturally at this range and global model resolution, there will be a fair amount of uncertainty as to the exact detail in development and areas affected.

Current thinking is a few scattered thunderstorms may develop during the mid/late evening hours across some southern counties of England, with activity becoming more widespread as the plume axis tracks northeastwards.

Greatest instability will be towards the SE, and hence higher probabilities (SLGT) of lightning have been included across portions of the Home Counties / East Anglia / Lincolnshire (21z-03z), with storms probably moving offshore across the North Sea through the early hours of Friday, despite heavy rain also affecting parts of northern England, albeit with a lower potential for lightning. Given high values of PWAT, local flooding is the primary concern (along with lightning), with a low risk of significant hail at this stage. There may be some imported elevated thunderstorms that develop across/near Cherbourg peninsula and travel across the English Channel, but this potential is less-supported in the global models currently (hence only an ISOL in these areas for now).

Several models also simulate an increase in lightning potential over the Irish Sea, running NNEwards into adjacent parts of Cumbria / S/SE Scotland 00z-06z. Have included a SLGT here for now to highlight slightly higher chances of lightning here also.

This is an advance forecast and should be used as a rough guide, as there will undoubtedly be changes made over the coming 48 hours, as is often the case in these convective events.

Very much agree with this...especially reference to the uncertainty

[Gordon Webb]

yes I am dubious too, after last fridays farce storm forecast for the north,    I know its hard to pinpoint where the storms will occur , but to claim ''thunderstorms are already marching northeastwards''  out of wales , when the rain band was not electrified in any way was just ridiculous thing to say

 

but lets leave that there,   

 

BBC this morning showing rain and lightning symbols across most of england and wales but after last friday I'd take that with a very large pinch of salt

Edited July 15, 2015 by Gordon Webb

[Spikecollie]

Look North forecast this morning mentioned thunderstorms Thursday into Friday for Yorkshire. As usual I'll take it as it comes, although the thought of another chance to sit up the garden watching incoming lightning over the Valley would be glorious. Minus the golf ball hail this time though, please...!

Edited July 15, 2015 by Spikecollie

[Harry]

It is looking like potential for lightning has increased I would suggest based upon the latest NMM. Indicating very marginal mid level instability along a line roughly from the SE up towards Northern Ireland, extending across NW England and into southern Scotland. Most instability and therefore highest probability of thunderstorms exists across SE, C/S England, E Midlands, EA up to around the Wash. 

 

Highest potential for surface based storms currently resides around C/S England, parts of the SW and Wales through the afternoon and evening, however precip does not seem break out until later in the evening so unlikely to be much surface based convection.

 

Latest NMM 5 keen to break out storms across S/E Midlands running NW, however I cannot emphasise enough that places south of say Birmingham do not benefit from much instability, so lightning coverage likely to be much more limited. MUCAPE coverage across the south is more extensive and stronger than yesterday. Latest NMM 5 also keen to restrict convective precip across the SE now, with little suggestion of imports...in all likelihood, the arrival of the flabby Low over N France during the evening, in my view, is likely to deflect any continental activity towards Benelux.

 

Still very changeable therefore but potential still around for thunderstorms tomorrow evening....for SE'rners, outlook less good than yesterday in my view (although abundance of energy there if it can be realised)

[NO LONGER POSTING]

So much model difference again!

 

 

[sunnijim]

Comparing the fax charts for Friday Midnight this week and Saturday midnight during the storm outbreak of two weeks ago 'to an untrained eye' there would appear to be a very simuler recipe,closer inspection of other parimeters would suggest our previous storms had better ingrediants to tap into,certainly for a more widespread event.

From what i can gather this morning a line from London into the East Midlands and Eastern England look like trigger zones,points South,West,and North of this less likely for thundery elements.

[Harry]

GFS 06z a move in the right direction...keen to break out (to my eye) surface based convection across Wales/SW mid to late afternoon, before (likely) elevated storms break out in similar locations to two weeks ago, spreading north-eastwards. GFS also appears to have ever so slightly advanced the pace and degree of instability. 

GFS definitely my favourite model at the moment

[Pat Butcher]

I'm not sure if all the pessimism in this thread is justified. Whilst there certainly won't be as large a convective outbreak as there was a couple of weeks ago, there certainly appears to be the possibility of elevated storms with a risk of severe hail/wind overnight on Thurs over a small patch anywhere within 100 or so miles of Northampton.. Am I missing something?

[Gordon Webb]

I'm not sure if all the pessimism in this thread is justified. Whilst there certainly won't be as large a convective outbreak as there was a couple of weeks ago, there certainly appears to be the possibility of elevated storms with a risk of severe hail/wind overnight on Thurs over a small patch anywhere within 100 or so miles of Northampton.. Am I missing something?

 

still looks more focused over the E/SE as sunnijim said in his previous post and there's still at least 30/36 hours to go

Edited July 15, 2015 by Gordon Webb

[Harry]

I'm not sure if all the pessimism in this thread is justified. Whilst there certainly won't be as large a convective outbreak as there was a couple of weeks ago, there certainly appears to be the possibility of elevated storms with a risk of severe hail/wind overnight on Thurs over a small patch anywhere within 100 or so miles of Northampton.. Am I missing something?

 

I think the dilemma is the behaviour of the models. Two weeks ago most models, even less than 24 hours pre-event, were suggesting similar to what is shown currently. Outbreaks of extensive precipitation chiefly across the Midlands/SW/Wales all trundling NE across the Midlands and NE. BBC Weather (not the only one by any stretch) followed the majority and predicted outbreaks of thunderstorms across these areas, away from the SE. Few models, as were favoured by myself and a number of others, preferred the GFS/NMM 5 resolutions which suggested convective outbreaks would primarily occur further east, where the instability was modelled to be (shock horror).

 

Currently, the BBC is modelling torrential downpours and thunderstorms in similar areas as before. I would agree, there appears to be marginally more instability on this occasion further N and W than there was two weeks ago. Furthermore, there is SBCAPE across C/S/SW England/Wales which if GFS is correct, will yield some surface based storms before the elevated storms kick in later. On this occasion we have a thundery low drifting N/NE from France which as ever brings an air of unpredictability and complexity...models currently think this wont serve to detonate any storms over N France, but the trough and CF advancing from the primary Atlantic Low will (little over the Continent therefore limited potential for imports it appears)....how they all interact is causing uncertainty and hence caution.

 

I think by tonight/tomorrow the place will be buzzing

[Gordon Webb]

I think the dilemma is the behaviour of the models. Two weeks ago most models, even less than 24 hours pre-event, were suggesting similar to what is shown currently. Outbreaks of extensive precipitation chiefly across the Midlands/SW/Wales all trundling NE across the Midlands and NE. BBC Weather (not the only one by any stretch) followed the majority and predicted outbreaks of thunderstorms across these areas, away from the SE. Few models, as were favoured by myself and a number of others, preferred the GFS/NMM 5 resolutions which suggested convective outbreaks would primarily occur further east, where the instability was modelled to be (shock horror).

 

Currently, the BBC is modelling torrential downpours and thunderstorms in similar areas as before. I would agree, there appears to be marginally more instability on this occasion further N and W than there was two weeks ago. Furthermore, there is SBCAPE across C/S/SW England/Wales which if GFS is correct, will yield some surface based storms before the elevated storms kick in later. On this occasion we have a thundery low drifting N/NE from France which as ever brings an air of unpredictability and complexity...models currently think this wont serve to detonate any storms over N France, but the trough and CF advancing from the primary Atlantic Low will (little over the Continent therefore limited potential for imports it appears)....how they all interact is causing uncertainty and hence caution.

 

I think by tonight/tomorrow the place will be buzzing

 

why are you letting some wasps in ?

[East_England_Stormchaser91]

Certainly looking likely that this could well be a possible notable event for some.

Certainly within the hi res reliable timeframe now.

Caution is still remaining with myself however. As we have seen this sort of thing shift eastward at the very last minute on past occurrences, with all the fun and games taking place across the water. Earlier this summer in June being a good example.

[Gordon Webb]

Certainly looking likely that this could well be a possible notable event for some.

Certainly within the hi res reliable timeframe now.

Caution is still remaining with myself however. As we have seen this sort of thing shift eastward at the very last minute on past occurrences, with all the fun and games taking place across the water. Earlier this summer in June being a good example.

 

if it shifts eastward from your location you'll need a boat to go out into the North Sea

[Sprites]

why are you letting some wasps in

my brothers dance CDs sound like a swarm of bees, perhaps thats buzzing hehehe.

why are you letting some wasps in

my brothers dance CDs sound like a swarm of bees, perhaps thats the buzzing hehehe.

Edited July 15, 2015 by Sprites

[Tim Bland]

A bit dissapointed there is no warning from Met office for tomorrow night.  Tells me they are not thinking it will be anything more than thundery showers at this point.

[Harry]

A bit dissapointed there is no warning from Met office for tomorrow night.  Tells me they are not thinking it will be anything more than thundery showers at this point.

 

Don't let the MetO be the primary guide as to whether thunderstorms take place.....believe me.

 

I suspect in all seriousness it's because of the slight variations in model output. I wouldn't be surprised for something to pop up later tonight or early tomorrow, initially for the SW/Wales then more broadly for much of England. But...thunderstorms do not always carry a MetO warning.

[Tim Bland]

Agreed Harry.  They will only warn for thunderstorms if they come with frequent lightening / hail / torrential rain.  Lack of warning suggests at the moment they think it will be the odd flash and moderate rain or thundery showers.  When we had the severe storms early in the month the warnings were out days in advance.  I have even seen warnings 48hrs out for Thundery showers. Not saying the warnings will not come but at this point it is safe to say that the experts don't think we will have anything severe or widespread. 

 

Meteo Group have a Level 2 (increased risk of thunderstorms) for Eastern areas for Mignight to 2am

Edited July 15, 2015 by Tim Bland

[Gordon Webb]

yep the storms on the 1st and 3rd of July I think were well warned at least 2 days in advance for some due to all the heat humidity that had been building for a few days

 

the warm humid air tomorrow will be arriving in the evening I think as the daytime warmth is subsiding and wont be hanging around either but I am surprised there's no warning about the strength of the wind considering the time of year

 

the wind speed may be typical for october/november but not July

 

GFS 12z looks to have diluted the precipitation a little bit at first glance and cape / LI looks less widespread too and the storm risk reduces quicker too through the evening after 9pm although not dying completely except Eastern england

Edited July 15, 2015 by Gordon Webb

[East_England_Stormchaser91]

Risk is definitely there. Actually looks similar to what we saw nearly 2 weeks ago, albeit less intense and further East. The same or very similar principals, parameters and mechanics are in place as what the 3rd July had looking at it from my view.

[sunnijim]

Don't let the MetO be the primary guide as to whether thunderstorms take place.....believe me.

 

I suspect in all seriousness it's because of the slight variations in model output. I wouldn't be surprised for something to pop up later tonight or early tomorrow, initially for the SW/Wales then more broadly for much of England. But...thunderstorms do not always carry a MetO warning.

Helen Willets still talking in terms of problomatic localised storms for areas mentioned already here, 'real deluges' rainfall wise. A met office yellow warning will appear tomorrow morning i would think.