Convective / Storm Discussion - 5th August onwards 2013

[Guest William Grimsley]

It looks like that Newton Poppleford Weather and SW England could see some heavy/thundery showers on Saturday, Sunday Evening and Monday Evening.

[biddie]

i have a feeling we will get some thunder in the early hours

[smoggyjester]

Reckon hampshire will get any tonight?

[East_England_Stormchaser91]

It has been a very poor year in general but for that 2 week spell at the end of July into the first couple of days of August. In that period I saw some of the best storms I have ever seen. We sure had to wait but for those that experienced the intensity of those storms the wait was worth it. Unfortunately we have reverted to waiting ever since though.

 

Must say I can't see tomorrow's storms being anything like as powerful as the 22nd/23rd July storms this year though, but even half as intense would still make a great storm

Very true, them storms were epic! 

[Ben Sainsbury]

ESTOFEX: 

 

British Isles

A mid-level low moves into the British Isles. Rich low-level moisture and increasing lapse rates result in CAPE during the day. Although vertical wind shear is weak, a tornado is not completely ruled out near sea breeze convergences. Additionally, excessive precipitation is possible with the slow-moving storms.

 

[ZONE 51]

http://www.estofex.org/ - here is the link to the above forecast.

 

 

SE - Also we could develop some lightning and thunder later tonight as a disturbance enhances showers, these could become heavy and thundery.

 

A look ahead (UK) ,all I can say is potentially thundery..

Edited August 21, 2013 by ElectricSnowStorm

[Coast]

Good morning storm fans!

 

Lets start off with a simple overview of the day by GFS:

 

 

Nice graphic showing possibilities in Wales and the Midlands late afternoon into early evening.

 

 

Transferring East into Norfolk as the night continues. Let me go and find some specific stuff to see what we might have in store.

[Guest William Grimsley]

ESTOFEX: 2013082306_201308212213_1_stormforecast.xml.png

 

British Isles

A mid-level low moves into the British Isles. Rich low-level moisture and increasing lapse rates result in CAPE during the day. Although vertical wind shear is weak, a tornado is not completely ruled out near sea breeze convergences. Additionally, excessive precipitation is possible with the slow-moving storms.

Newton Poppleford Weather is right on the border-line. Damn.

Edited August 22, 2013 by William Grimsley

[Coast]

GFS from Lightning Wizard shows the CAPE potential if we can tap into it:

 

 

 

 

 

Convergence right over London, the Home Counties and lower Midlands:

 

 

Transferring East into EA early evening:

 

 

Some heavy convective showers associated with it?

 

 

Lower level lapse rates steepening:

 

 

MCS prorogation and PWAT moving across the Midlands and into EA through the late afternoon:

 

 

Still hanging on in Norfolk through the evening:

 

[Supacell]

I finish at 2pm today so i am hoping to storm chase. Currently not sure which way to head but looks like I won't have to travel too far away from home.

On a set up like today would anyone bet against Lincolnshire being a hot spot :-P

Edited August 22, 2013 by Supacell

[ChezWeather]

I finish at 2pm today so i am hoping to storm chase. Currently not sure which way to head but looks like I won't have to travel too far away from home.

On a set up like today would anyone bet against Lincolnshire being a hot spot :-P

Hopefully you will see something if you stay put 

[Coast]

I finish at 2pm today so i am hoping to storm chase. Currently not sure which way to head but looks like I won't have to travel too far away from home.

 

I reckon you should drop onto the Lincs/Norfolk border around 4.00pm and watch the radar as it sweeps Eastwards. I've animated the NMM MLCAPE and TT Index charts to show a potential scenario for later and you can see how a band moves through the lower Midlands and onto the coast of East Anglia/Essex/Kent early evening:

 

 

 

 

Maybe even I'm in with a rumble or two later down here?!

[Coast]

Here's a taster Skew-T for Kings Lynn at 18z:

 

 

Not too shabby at all!

 

http://www.skystef.be/storm-indices.htm

 

 

 

 

 

[Summer Sun]

Synopsis

 

Upper trough, with axis over northern England at midnight, will track southeastwards through Thursday, becoming a cut-off upper low over the East Midlands by mid-afternoon. At the surface, advection of a warm and humid airmass will take place during Wednesday, with this airmass still present through Thursday. Meanwhile, a weakening cold front will continue to migrate southwards across England and Wales.

 

Discussion

 

Through the first half of this forecast period, an area of showery rain (from mid- and high-level cloud) is expected to develop across central and southern Britain, as a shortwave trough runs eastwards across these areas ahead of the advancing weak cold front.

During Thursday daytime, heating of the warm, moist surface airmass will generate 500-800 J/kg CAPE. With upper low aloft and low-level convergence/confluence (especially with aid from sea breeze development) and local topography, scattered showers and a few thunderstorms are forecast to develop, thunderstorms most likely in the SLGT area. Shear is rather weak (~20kts) so organisation of cells will be limited somewhat, and hence the risk of severe weather is considered fairly low. However, PWAT values of 30-35mm combined with slow storm motion may result in local flash flooding from prolonged downpours, while hail up to 1.5cm in diameter is possible from any stronger cells given dry air aloft.
There may be the potential for a funnel given relatively low LCLs (especially during the late morning and again into the evening) and low-level convergence.

 

http://ukasf.co.uk/storm-forecasts/274

 

 

[Nick F]

Storm & Convective Forecast - Issued 2013-08-22 09:21:02

Valid: 22/08/2013 1000z to 23/08/2013 0600z

Headline: THERE IS A RISK OF THUNDERSTORMS FORECAST

Synopsis
A weak mid-level low will move SE across England and Wales today, with a slack warm/moist surface flow across England which will become increasingly unstable this afternoon with any surface heating.

... E WALES, CENTRAL, SOUTHERN & EASTERN ENGLAND ...

Colder air in the mid-levels associated with the mid-level low will override a zone of warm/moist air at the surface across E Wales, southern/central/and eastern England - creating steep lapse rates. Morning cloud and outbreaks of rain should clear away east this afternoon with any cloud breaks allowing surface heating to generate 400-800 j/kg CAPE in the moist airmass with steep lapse rates. Therefore scattered heavy showers and thunderstorms are likely - mainly to the north of the M4 corridor/London. Showers/storms will be slow-moving with a risk of high-rainfall totals over some locations leading to localised flooding. Lines of showers/storms may focus near forecast wind/sea breeze convergence setting up from East Anglia up through Lincs and N/E Yorks - and despite weak vertical shear - funnels or even a weak tornado can't be ruled where stronger updrafts rotate along the convergence zone.

Issued by: Nick Finnis

 

Also can be found here: http://www.netweather.tv/index.cgi?action=convective;sess=

 

 

[johnholmes]

first class analysis as always from Nick, the predicted ascent for Doncaster would give tops with T and Td expected to quite a bit over 30,000ft during the afternoon and evening, so east of here, as suggested, with the prospect of convergence/sea breezes must be good locations for any chasers? Lincs especially but possibly use the A1 as an approximate line and east of there from N Yorks south?

Edited August 22, 2013 by johnholmes

[Chris.R]

Nout here again then. This is truely the worsed year for lightning ever. No wonder there are no northwesterners posting on here anymore.

[Guest William Grimsley]

 

Maybe even I'm in with a rumble or two later down here?!

 

Now, I say! Is that light purple stuff good?

[Coast]

Now, I say! Is that light purple stuff good?

 

Not really :unsure: 

[Supacell]

first calss analysis as always from Nick, the predicted ascent for Doncaster would give tops with T and Td expected to quite a bit over 30,000ft during the afternoon and evening, so east of here, as suggested, with the prospect of convergence/sea breezes must be good locations for any chasers? Lincs especially but possibly use the A1 as an approximate line and east of there from N Yorks south?

Yes John i was thinking A1 as a good north south route for today. Currently near to Mansfield with work so will aim for Newark as a start point around 2pm.Tops over 30,000ft could mean some quite prolific lightning in any thunderstorms that form. Dry air aloft and these cloud tops could also make for nice clear anvils visible from a fair distance away and hail underneath.

[Guest William Grimsley]

Not really

Explain?

[ChezWeather]

Well it certainly feels humid here. Just keeping my fingers crossed that im not too far west for any action. 

[Harry]

Explain?

 

TT index looks at storm strength - I looked up on google the following chart which aids the chart interpretation

 

44 Convection not likely

44-50 Likely thunderstorms

51-52 Isolated severe storms

53-56 Widely scattered severe

56 Scattered severe storms

 

The purples on the chart indicate values way down in the 30s - therefore, convection is unlikely in areas shaded white/purple/blue.

 

On this sort of chart ideally you want to be under yellows/oranges/reds....rather confusingly, on a CAPE chart, purple indicates extremely high convective potential....isnt it all confusing

 

Coast I'm sure will have a much better grasp of a TT chart than me

Edited August 22, 2013 by Harry

[Supacell]

Explain?

Briefly that chart shows the TT index. Using the colour scale to the right of the map, the colours towards the top of the scale are indicative of a higher likelihood of thunderstorms and those at the bottom a lower risk. You want oranges and reds for good thunder potential.Edit: Harry beat me to it and his explanation better than mine but essentially the same thing. Edited August 22, 2013 by Supacell

[Coast]

Coast I'm sure will have a much better grasp of a TT chart than me

 

I think you've answered that thoroughly H! Remember the TT index is only a guide to be used with other indicators and experience - it has it's followers and non-followers.

 

Total-Totals Index - A stability index and severe weather forecast tool, equal to the temperature at 850 mb plus the dew point at 850 mb, minus twice the temperature at 500 mb. The total-totals index is the arithmetic sum of two other indices: the Vertical Totals Index (temperature at 850 mb minus temperature at 500 mb) and the Cross Totals Index (dew point at 850 mb minus temperature at 500 mb). As with all stability indices there are no magic threshold values, but in general, values of less than 50 or greater than 55 are considered weak and strong indicators, respectively, of potential severe storm development.

 

http://www.srh.noaa.gov/oun/?n=spotterglossary4