Storm & Convective Discussion 12z 21/7/14 ------>

[Greeny]

The 12Z run for GFS. Early run looks like things are springing up for Friday potential wise. I circled an area which shows high wind shear with CAPE and -LI values fit for storms on the west coast. Deep layer shear seems to be at reasonable values around most of the country by the looks of it so could Friday bring something severe?

 

 

Saturday still looking ripe for storms and an even bigger area for shear in excess of 30knts I think the upcoming days are going to be interesting convective wise to say the least better though to look at it nearer the time

 

 

12z run for precipitation charts, looks like a similar pattern from the 00z run.

 

 

NMM precip at 14Z and 17Z

 

 

 

 

[Nick F]

Colder mid-level air spreading east in association with upper trough expanding south across the east Atlantic Thursday and Friday will steepen lapse rates across many parts tomorrow, which combined with modest surface heating, will create an increasingly unstable airmass across much of the UK and Ireland away from the SE of England.

 

A shortwave impulse embedded in the strong upper flow around the upper trough will move E across the UK, will create large scale ascent and will time favourably with peak surface heating to support scattered t-storms by late morning/early afternoon.  

 

Although vertical shear will be fairly weak generally across the UK ... fairly strong SWly winds above 700mb ahead of shortwave across Wales, central and parts of eastern England may allow line segments or clusters of storms here - capable of producing damaging wind gusts and marginally large hail (1-2cm). Not so sure about supercells though, given weak vertical shear, but can't be ruled out I suppose.

 

Otherwise, storms further north across Scotland and Northern Ireland will be more poorly organised, given lighter winds aloft. Though any storms will be capable of producing localised flooding, gusty winds and hail.

Edited July 30, 2014 by Nick F

[Greeny]

Colder mid-level air spreading east in association with upper trough expanding south across the east Atlantic Thursday and Friday will steepen lapse rates across many parts tomorrow, which combined with modest surface heating, will create an increasingly unstable airmass across much of the UK and Ireland away from the SE of England.

 

A shortwave impulse embedded in the strong upper flow around the upper trough will move E across the UK, will create large scale ascent and will time favourably with peak surface heating to support scattered t-storms by late morning/early afternoon.  

 

Although vertical shear will be fairly weak generally across the UK ... fairly strong SWly winds above 700mb ahead of shortwave across Wales, central and parts of eastern England may allow line segments or clusters of storms here - capable of producing damaging wind gusts and marginally large hail (1-2cm). Not so sure about supercells though, given weak vertical shear, but can't be ruled out I suppose.

 

Otherwise, storms further north across Scotland and Northern Ireland will be more poorly organised, given lighter winds aloft. Though any storms will be capable of producing localised flooding, gusty winds and hail.

 

I was looking at the helicity charts over at lightning wizard earlier and there was none showing for the UK but the MCS had stronger potential. With wind shear, what chart do you look at to find out if it is verticle or horizontal? Reasonable DLS is showing on GFS.

 

Edit: have I already determined it with the charts I have already looked at

Edited July 30, 2014 by Greenday

[Nick F]

I was looking at the helicity charts over at lightning wizard earlier and there was none showing for the UK but the MCS had stronger potential. With wind shear, what chart do you look at to find out if it is verticle or horizontal? Reasonable DLS is showing on GFS.

 

For horizontal or speed shear, I tend to look at the 500mb and 300mb wind speed charts - they show if there is a jet streak. Tomorrow there is a mid-upper level SWly jet across England and Wales just ahead of the shortwave moving east. These stronger winds aloft help vent and organise the storms into lines or clusters.

 

For vertical shear, I use the DLS (deep layer shear - usually 0-6km height) or LLS (low-level shear - usually 0-1km height) - higher values tend to indicate veering and strengthening of winds with height - which increase the chances of rotation of storms - thus risk of large hail and also tornadoes if LLS shear is strong.

Edited July 30, 2014 by Nick F

[Greeny]

Oh yes I see the jet streak, thanks Nick for that little tip I thought that DLS looked quite reasonable to most thunderstorm days perhaps not enough for supercell formation although I do notice over 30knts forecast over in east anglia according to NMM.

[Nick F]

Storm & Convective Forecast

 

 

Issued 2014-07-31 07:05:54

Valid: 31/07/2014 0600z to 01/08/2014 0600z

 

THERE IS A RISK OF THUNDERSTORMS FORECAST

Synopsis

Long-wave upper trough will expand south across the east Atlantic towards the British Isles and further south over the next 24-36hrs. Surface low pressure will be centred close to northern Britain, with an unstable westerly flow northwest of a line from  Dorset to Suffolk.

 

... SW ENGLAND, WALES, MIDLANDS, N ENGLAND, LINCOLNSHIRE, NORFOLK ...

 

Colder mid-level air spreading east in association with upper trough expanding south will steepen lapse rates which, combined with modest surface heating, will create an increasingly unstable airmass across much of the UK and Ireland away from the SE of England. A shortwave trough embedded in the strong upper flow around the long-wave upper trough will move E across the UK, allowing large scale ascent and will time favourably with peak surface heating to support scattered t-storms by late morning/early afternoon. 

 

Although vertical shear will be fairly weak generally across the UK ... fairly strong SWly winds above 700mb ahead of shortwave across England and Wales, may allow line segments or clusters of storms to develop across Wales, Midlands and parts of eastern England  - these storms capable of producing damaging wind gusts and marginally large hail (1-2cm). Also, storms may produce slow-moving torrential downpours, bringing a risk of localised flooding.

 

... EIRE/N IRELAND, SCOTLAND ...

 

Otherwise, storms further north and west across Scotland and Eire/N Ireland will be more poorly organised, given lighter winds aloft. Though any storms, given their slow-moving nature, will be capable of producing localised flooding, along with gusty winds and hail.

 

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

Edited July 31, 2014 by Nick F

[vladthemert]

thinking next three days might be some fun.   Thanks Nick F for the forecast everyone else who provides them.   Just reading forecasting it seems it shifted southwards and the jet unlikely to be factor now according Tony Gilbert though still good chance organised thunderstorms.  Can read latest here at the bottom.

 

http://www.ukweatherworld.co.uk/forum/index.php?/topic/104422-convective-outlook-thurs-31st-july-2014/

 

storm clouds developing already huge plumes

Edited July 31, 2014 by vladthemert

[BrickFielder]

 Some slight differences across the models.

 

One I would like to pick up on relates to the suffolk and essex area late afternoon  (1600 to 1800).  NMM is suggesting a low level convergence zone here.

500hpa humidity charts suggest a potential cap breaking here as moisture gets pooled.

Other models dont seem so keen on it. Forecast SkewT suggests turning winds in the lowest level and it just about taps into the jet above.

Maybe cloud tops will not be high enough here with cooler drier air not quite arriving on time.

 

Second one I would like to pick up on relates to the Liverpool and Manchester area again during the late afternoon.There is marginally greater deep layer shear here as well.

 

SkewT suggests tops upto 350hpa with the cooler drier air aloft.

 

Two important charts for me are the following today.

700Hpa vertical velodity charts are not that impressive. Looking at Satelite pictures there might be some cloud ahead of the front and timing looks a touch late to match the models. Some evidence of a line of convection out to the west of Wales. Key area Likely to be south wales and am not convinced about development for the midlands.

 

Tricky to call. Think cells developing over south wales will travel into the midlands on the back of 500hpa winds.  Think you are better off looking at the radar than models for today.

 

 

 

 

 

 

 

[TonyH]

Sferics over the Irish Sea from showers heading to North Wales

[Supacell]

The expected distinct bands of showers are now starting to materialize, although nothing thundery on any of them as yet. The northern band is making a bee line for Derby, now it just needs to fire up.

[Flash bang flash bang etc]

Slightly off topic for the current band of showers & storms but I noticed storm potential for early hours of Tuesday... We even got a lightning symbol!

Any chance this afternoon's activity will last down into Hants?

Edited July 31, 2014 by Flash bang flash bang etc

[Supacell]

Slightly off topic for the current band of showers & storms but I noticed storm potential for early hours of Tuesday... We even got a lightning symbol!Any chance this afternoon's activity will last down into Hants?

 

Today's activity is not thundery as yet, but I can foresee some sparks as it heads east. However, I would doubt activity would get as far south as Hants today, more likely tonight but as a dying band of showers. Plenty more opportunities with low pressure taking charge over the weekend.

[Supacell]

We have lightning now in the Ludlow shower...

 

... and it's died out 

Edited July 31, 2014 by Supacell

[TheToastPeople]

Im looking forward to seeing some rain at this point, all the grass has started to fade. Wish these storms would hurry up, i have work in an hour!!! Good luck fellow storm fans!

[TonyH]

Sferic south of Redditch, they could be a bit livelier developing over South Midlands

[lassie23]

Looks like the South East will stay dry until Saturday! Met office weather warnings are for up north at the moment!

[TonyH]

It has turned quite lively near Warwick

[Supacell]

Multiple strikes around Henley, Warwick, Kenilworth area..then possibly Coventry again? They had that last quite vicious storm a week or so ago. I knew it lol, E Mids Notts and Lincs now on alert

 

It does looked to have kicked off around that neck of the woods. I am not sure about that track though, it looks more to head to the south of Leicester and then into South Lincolnshire. This is if it was to keep going of course, currently storms do seem to be pulsing but if they can just get that bit more cloud height then the risk of something more organised.

 

It's back building too, more cells now near to Worcester.

Edited July 31, 2014 by Supacell

[johnholmes]

look at the 700 and 500mb flows, easy to show them on the radar Extra?

[skyblusam]

Rumbling away like mad here.no rain as yet but constant thunder for about 10mins now. Not seen any lightning yet

[TonyH]

Quite a severe storm (s) over Warwickshire now, Dad has it at Rugby.

[TonyH]

One over Bedworth too now! Gordon

[Rammie]

I'm in Kettering and I am waiting!

[skyblusam]

wow the rain came and boy was it heavy.

[Supacell]

Looks like that area of storms has become somewhat organised and forming into a multi cell cluster, heading just north of east to likely track south of Leicester, Rutland and then possibly toward Stamford and Peterborough.

 

I have finished work now but will sit this one out, the fact it is around 40-50 miles away and the likelihood of rush hour traffic indicates to me that trying to chase would be a fruitless exercise. However, if you live in southern Leicestershire get those camera's ready

 

Kettering looking good for a hit from a new cell to the south over Daventry currently.

Edited July 31, 2014 by Supacell