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

[Gordon Webb]

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Is this what's causing all the current humidity?

;-)

 

I suppose it depends on what your doing to generate heat

[Harry]

Well ain't this interesting...

 

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As is this for my location same time tomorrow night, lol

[Flash bang flash bang etc]

As is this for my location same time tomorrow night, lol

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Google weather is starting to come on board regarding thunderstorms for my area at least. Yesterday it just said 'showers' but now it's 'isolated thunderstorms' - so headed in the right direction at least :-)

And this is the risk map just released on UKWW - which is pleasant news for us storm-starved southerners... ;-)

[IanR]

To be fair though, you're in the South East, so you will get something no matter what or where the risk area is. That was the case last time - your area wasn't forecasted anything, yet you still got severe thunderstorms.

+1

[IanR]

just cant get excited about thursday nights potential in this area, i suppose the odd flash of distant lightning towards the east is the most i can expect at best, but not getting hopes up even for that lol  , the storm of 1st july kind of used up our yearly allocated quota of thundery activity

[Harry]

To be fair though, you're in the South East, so you will get something no matter what or where the risk area is. That was the case last time - your area wasn't forecasted anything, yet you still got severe thunderstorms.

Worth clarifying that not everywhere in the SE had storms a few weeks ago. Also, there were a few reliable models directing towards the SE being hit so it wasn't a surprise to be fair (not to me anyway).

Tomorrow night less clear cut...the chart posted above from UKWW I think is pretty much on the money and, after my review of the models a few hours ago, is how I saw my own risk chart looking tomorrow. As of this evenings model outputs I think it's pretty much on the money.

[NO LONGER POSTING]

Google weather is starting to come on board regarding thunderstorms for my area at least. Yesterday it just said 'showers' but now it's 'isolated thunderstorms' - so headed in the right direction at least :-)

And this is the risk map just released on UKWW - which is pleasant news for us storm-starved southerners... ;-)

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If only...

[marksp]

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like the look of that Map !!

 

leaving the beautiful hills and dales of North Derbyshire tomorrow for 4 days in London, might see some good storms, fingers crossed

[tomp456]

Not in range tomorrow, it's a shame cuz we could really do with a storm or at least the heavans opening. Dunno what the humidity was around lunchtime but I could almost taste the water in the air.

[Harry]

Not in range tomorrow, it's a shame cuz we could really do with a storm or at least the heavans opening. Dunno what the humidity was around lunchtime but I could almost taste the water in the air.

GFS and NMM5 both give you some potential - would charge the camera just in case

[80sWeather]

Love it...agreed that the Synoptics are very similar indeed. Would love to know the full extent of storms for that set up.

Was 26 at the time. After a night out we watched this beast creep towards us as we sat on a roof near Bourne Cambridgeshire.

Constant crawling lightning with no rain for What seemed like hours.

Great times!

Edited July 15, 2015 by 80sWeather

[Nick F]

Storm & Convective Forecast

Issued 2015-07-15 21:56:24

Valid: 16/07/2015 0600z to 17/07/2015 0600z

 

 

CONVECTIVE/STORM OUTLOOK -THURSDAY 16TH JULY

 

Synopsis

Upper trough to the west of the British Isles will drift slowly east on Thursday eroding the ridge present earlier in the day. An upper shortwave trough in the strong upper flow rounding the base the upper trough will track northeast and aid the development of an usually deep surface low (for July) that will track N up the western side of Ireland later Thurs and early Fri. Warm front associated with the low will lift north across England and Wales during the day, introducing a warm, humid and increasingly unstable airmass from the south. A cold front will move in from the SW early Friday morning, clearing all but the far north of Scotland by 12z Friday

.

... S/SE WALES, CENTRAL, SERN and ERN ENGLAND ...

 

Warm/moist air, characterised by high 0-1km theta-w (wet bulb potential temp) values of around 16-18C, will spread north during the afternoon and evening across the above areas. An elevated mixed layer (EML) on the near continent, characterised by steep lapse rates, will overlap this warm and moist air at the surface, yielding a pool of 400-800 j/kg MLCAPE across the above areas between 18z Thurs - 06z Fri before the cold front removes the unstable plume away to the east. The EML will most likely cap any surface based convection developing, with the temp needed to break the cap unlikely reached. However, falling heights with approaching upper trough and attendant shortwave trough moving NE should create sufficient large scale ascent, coupled with cooling mid-levels, for scattered elevated thunderstorms to develop and merge moving NE later Thursday evening and overnight into Friday morning before clearing into the N Sea. Strengthening mid-upper SWly winds while winds are backed SEly at the surface ahead of the cold front is indicated to provide 40-50 knts of deep-layer (0-6km) shear. This will support multicell line segments or perhaps even high-based supercells capable of producing large rainfall totals in a short space of time leading to flash-flooding, strong wind gusts, frequent cloud-to-ground lightning and an isolated large hail risk - therefore have issued a SLIGHT risk. Storms may merge to form a MCS, ECMWF for example has one moving NE from London across E Anglia/E England to N Sea, with excessive rain and lightning the main risks.

 

... IRELAND, N IRELAND, WALES, SW ENGLAND, N ENGLAND ....

 

Warm moist air advection ahead of low arriving close to western Ireland and cool air advection in the mid-upper levels, as upper trough edges in from the west, is indicated to yield a few 100 j/kg CAPE later in the evening/overnight. Large scale ascent ahead/along cold front will allow embedded convection with lightning in the general rain spreading in across EIRE/N Ireland in the evening and later Wales and N England. A few surface based storms developing over higher parts of Wales, SW England and Ireland in the late afternoon or early evening can't be ruled out ahead of this thundery rain, rooted in the boundary layer, these storms will benefit from strong deep layer shear and low-level shear and will quickly organise - so hail, flash flooding, strong wind gusts are possible, low LCLs and veering winds with height suggest and isolated tornado also can't be ruled out. A MARGINAL risk of severe weather seems sufficient for these areas given lower CAPE indicated towards SE England.

 

 

 

Edited July 15, 2015 by Nick F

[Pat Butcher]

Seems to be agreement from some of the convective guys - UKASF have just bashed this one out:

Day 2 Convective Outlook

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

ISSUED 21:53 UTC Wed 15 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.

However, there is some scope across parts of Wales/West Country for isolated sfc-based convection to develop late afternoon/evening hours, given 700-900 Jkg-1 SBCAPE, increased forcing from aloft and some surface convergence. Forecast profiles look quite dry, and so whilst convective cloud will likely develop, it is uncertain whether it will reach a depth sufficient for lightning activity - hence for now we remain with an ISOL and will monitor convective trends for any potential upgrades.

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 there is still a reasonable amount 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, eventually exiting to the North Sea - areas at greatest risk are thus highlighted with a SLGT and MDT (20z-04z), with instability increasing (but upper forcing decreasing) as one heads farther to the SE.

At present there appears to be a lack of upper forcing to generate imported elevated convection from France (especially Cherbourg and environs), and hence for now Channel and adjacent coastal areas remain at ISOL.

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, albeit this signal less clear compared with NWP guidance yesterday. Retaining SLGT for now, but may need a downgrade if this trend continues.

Conversely, parts of Ireland/Northern Ireland may need an upgrade to SLGT, especially northern and western areas.

Source:http://www.convectiveweather.co.uk/forecast.php?date=2015-07-16

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Edited July 15, 2015 by Davethedog

[tomp456]

GFS and NMM5 both give you some potential - would charge the camera just in case

If I did that then storm potential goes to 0% regardless of computer predictions

If anything happens it will have to be recorded on the iPod lol

[Pat Butcher]

Right on cue, Estofex have climbed on board! Are you storm guys all wired into some sort of matrix together?

Storm Forecast

Valid: Thu 16 Jul 2015 06:00 to Fri 17 Jul 2015 06:00 UTC

Issued: Wed 15 Jul 2015 22:04

Forecaster: GATZEN

A level 2 was issued for parts of NW Germany, Benelux, N France, and S UK mainly for large hail, severe wind gusts, and to a lesser extend tornadoes and excessive precipitation.

A level 1 was issued for central and southern France, and NE Spain mainly for large hail and severe wind gusts.

SYNOPSIS

At the southern flank of low geopotential across Scandinavia and between Iceland and the British Isles, a rather zonal flow has advected moist air into Europe. Soundings from northern France/southern UK to western Germany indicate rich and deep moisture with surface dewpoints around 16°C. South of this frontal zone, a ridge is present, and steep lapse rates have spread from northern Africa into SW Europe.

On Thursday, the north-west European trough will move southward. Together with another low W of Iberia, it yields a south-westerly flow across western Europe. Advection of warm and well-mixed air masses is expected until the end of the period, when the axis of warm air will reach from central France to south-western Germany. Ahead of a cold front across the eastern UK and western France, a strong low-level jet will spread into the Benelux countries and NW Germany at the end of the period.

DISCUSSION

Southern/eastern UK into northern France, Benelux, and NW Germany

The warm air advection regime will see quickly improving lapse rates atop of a moist boundary layer from W Germany across Benelux into northern France and the southern UK. Given the rich low-level moisture, model CAPE values of 1000 J/kg MLCAPE seem to be reasonable during the afternoon and evening. Initiation becomes likely in the evening hours due to the approaching cold front and frontogenetical forcing. QG forcing will increase across the UK due to DCVA.

Storms are forecast to form across northern France in the late afternoon, spreading eastward into the Benelux in the evening. Additional storms may develop across southern and eastern UK. Due to the strong low-level jet, 15 m/s low-level vertical wind shear will be available, and storms can quickly become supercells, capable of producing large hail, severe wind gusts, and flash flood. Tornadoes are also forecast with the highest threat in the evening hours from Belgium into the SE UK. Strong tornadoes are not ruled out given the strong low-level jet and associated vertical wind shear.

In the evening and night hours, storms are forecast to cluster, spreading north-east. Severe threat will gradually weaken as storms become elevated, but given the strong low-level jet and ongoing frontogenetical forcing, threat of large hail, severe winds, tornadoes, and excessive rain is expected to continue until the early morning when the main activity is expected to shift to western Germany.

Central and southern France, north-eastern Spain

Hot and well-mixed air mass will be present ahead of an approaching cold front from the west. Low-level moisture is expected to be limited, but some moisture advection takes place from the north Mediterranean, especially to the north of the Pyrenees. Initiation of storms is forecast ahead of the approaching cold front from SE Spain to southern France and further into central France. Storms that form will have a potential to produce severe downbursts given the well-mixed low-level air mass. Additionally, vertical wind shear around 10-15 m/s in the lowest 3 km will allow for well-organized storms including supercells, capable of producing large or very large hail. Given the large cold pool potential, storms are forecast to cluster before they spread north-eastward in the evening and night.

[ChezWeather]

Looking like a fairly average change for my area, night time storms though, so they can be 50 miles from here and i will still be happy! 

 

Good luck everyone, this thread will probably be alot livelier Thursday night / Friday morning. 

Edited July 15, 2015 by ChezWeather

[Flash bang flash bang etc]

Oooooh I'm loving that estofex map!!

So the question is whether to chase towards Cambridge or stay put in Guildford...

[Gordon Webb]

Oooooh I'm loving that estofex map!!

So the question is whether to chase towards Cambridge or stay put in Guildford...

 

not that I want a storm but IF i did I think both have possibilities but I'd plump for cambridge

[Daniel*]

not that I want a storm but IF i did I think both have possibilities but I'd plump for cambridge

Guildford 100%. This is where storms which initiate are more likely to be more severe. Estofex update is great and slightly worrying I do not want a strong tornado over my house but fascinating whatever the outcome.

[East_England_Stormchaser91]

Guildford 100%. This is where storms which initiate are more likely to be more severe. Estofex update is great and slightly worrying I do not want a strong tornado over my house but fascinating whatever the outcome.

Will be a case of now casting yet again. Somewhere like Cambridge way into Suffolk could well be the sweet spot where these storms look to mature if they do form.

Good luck to all and what a pleasant surprise this is!

[fazer76]

As ever predicting a possible thunderstorms arrival, location, duration and of course intensity looms for the next few hours and on. My guess this time tomorrow we'll be far better informed. Trust me. Nowcasting and storms are name of the game if you're prepared to be sensible or realistic about things.

[fazer76]

I suppose it depends on what your doing to generate heat

Knitting?