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Storm/Convective Technical Analysis Discussion 17/7/2014 onwards

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*Copied from the SE/EA thread, feel free to fill in the gaps as my experience at this isn't great and I'm sure there are other factors to address other than the ones I have stated*

Right T-day (terrible pun I know)

Saturday

temperatures

Posted Image

Looks hot, the track of Fridays MCS looks to be through central England so there is every chance that Eastern areas could remain clear.

 

Dew points

Posted Image

Reaching 22C by the afternoon and carrying on into the evening.

 

Cape

Posted Image

Off the scale by late Afternoon

Same at the mid-levels

I think there is definitely a chance of something developing during Saturday that could be quite violent.

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*Copied from the SE/EA thread, feel free to fill in the gaps as my experience at this isn't great and I'm sure there are other factors to address other than the ones I have stated*

Right T-day (terrible pun I know)

Saturday

temperatures

Posted Image

Looks hot, the track of Fridays MCS looks to be through central England so there is every chance that Eastern areas could remain clear.

Dew points

Posted Image

Reaching 22C by the afternoon and carrying on into the evening.

Cape

Posted Image

Off the scale by late Afternoon

Same at the mid-levels

I think there is definitely a chance of something developing during Saturday that could be quite violent.

Wow thanks for posting - positively mouthwatering!!! 3000K/Jg and LI-11 at 8pm!?!?!?!????

Phwoooar!!! Let's just hope the CF can hang back for long enough to allow that to build...if it shifts sooner this is just a fantasy

Edited by Harry

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Strikes just showed up near London. Huh?

From the eastern end of the trough maybe.

Edited by poseidon

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Netweather Storm forecast issued early Thurs evening until noon tomorrow in case anyone missed the link as it disappeared in the general convective thread:

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

Edited by Nick F

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a repost of Nick Finnis's preliminary thoughts on storm prospects for the next 24 hours.......thanks Nick!

 

"My forecast yesterday underestimated the eastward extent of the storms, mainly because the models, particularly the Euros, had the emphasis of storms tracking north across central and western areas, though GFS was more eastward across the SE/E Anglia. Not that I'm complaining, despite being woken at 2.40am then again just before 5am by storms.

 

Storms will rumble on north over England and Wales towards southern Scotland this morning and into the aftenroon, brief ridging taking over from the south allowing a mainly very warm or hot day across England and Wales. Then all eyes south for the 2nd installment coming up from France tonight. This 2nd bout could be potentially more organised and severe - particularly across central S and SE England, The Mids and E Anglia into early Saturday. The low level southerly jet strengthens and the flow backs more SE'erly, as the upper long-wave trough to the west takes on an increasingly negative tilt, this will increase vertical shear - allowing the possibility of an MCS with bowing line segments on its forward side bring the risk of damaging wind gusts and also one or two supercells could be embedded. Large amounts of MLCAPE shown by GFS suggests threat of large hail, frequent cloud-ground lightning. PWAT (precipitable water) values of 39mm are very high- so excessive rainfall and flash flooding are a real threat too.

 

Some charts from lightning wizard for 3am show the potential:

 

0-6km shear/tor paramter:

Posted Image

 

SRH/supercell parameters:

Posted Image

 

Bit too busy this morning, but will probably issue a new storm forecast early afternoon."

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The SE of England is still due to have CAPE/LI reach impressive levels overnight:

 

post-5886-0-41265200-1405671848_thumb.pn

 

However, (partially from an IMBY perspective) not all will necessarily generate storms.  There appears to be significant capping (though I defer to more knowledgeable members to correct me if I'm not interpreting this correctly!) affecting Kent in particular:

 

post-5886-0-60131100-1405671847_thumb.pn

 

This would seem to tie in with the Estofex Level 2 forecast which notes:

 

 

 

The main question will be how many storms will be able to form in this environment, which is in principle capable of sustaining extremely severe storms. Another question is whether the storms will be surface-based.

Current thinking is that the air-mass slightly to the east of the surface convergence line will be strongly capped. 

 

So, as always, some will see impressive storms and some won't.  Window-based nowcasting is probably your best bet! :)

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Overnight

 

Still a complex setup but it looks like from about late evening a severe storm in terms of lightning crosses into kent and moves up through into east anglia.

post-2809-0-08595000-1405692527_thumb.pn

 

A little later from about 2am onwards another pulse of storms move up across the isle of wight into the midlands.

post-2809-0-28119500-1405692545_thumb.pn

 

Since these form in a spanish plume environment and are crossing the UK overnight then there is a good chance that they will not be surface based. (sometimes storms can modify their environment to be surface based)

post-2809-0-51958000-1405692785_thumb.pn

 

The high cloud tops associated with these storms would be condusive to lightning. So dont be surprised if you get an early wake up call.

 

Tomorrow

 

I am not to keen on putting much detail on tomorrow at this point. There are perhaps a few charts though that should be pondered on.

post-2809-0-84248900-1405692962_thumb.pnpost-2809-0-23098400-1405692948_thumb.pn

 

The highest instability (Cape ) is not necessarily where storms will develop. You need to take into account convection inhibition  (CIN) and where the forcing mechanisms are (vorticity - surface winds).

post-2809-0-43140600-1405693104_thumb.pn

Mid level lapse rates tend to decline over the UK tomorrow which limit storm severity.

post-2809-0-06777900-1405693170_thumb.pnpost-2809-0-19440500-1405693184_thumb.pn

 

The frontal boundary becomes more marked as the day goes on tomorrow and a lower tropopause means lower cloud tops.

 

It is still too early to tell about tomorrow, but it looks like a Cap (just over 900hpa) goes during the afternoon and when combined with some low level convergence and a low level jet (925hpa wind) then there is a window for some severe storms to develop despite some of the factors mentioned above.

 

Edited by BrickFielder

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*Copied from the SE/EA thread, feel free to fill in the gaps as my experience at this isn't great and I'm sure there are other factors to address other than the ones I have stated*

Right T-day (terrible pun I know)

Saturday

temperatures

 

Looks hot, the track of Fridays MCS looks to be through central England so there is every chance that Eastern areas could remain clear.

 

Dew points

 

Reaching 22C by the afternoon and carrying on into the evening.

 

Cape

 

Off the scale by late Afternoon

Same at the mid-levels

I think there is definitely a chance of something developing during Saturday that could be quite violent.

 

But again that's not the current direction of the storms over france, watch the sat image

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Storm & Convective Forecast

Posted Image

 

Issued 2014-07-18 14:37:16

Valid: 18/07/2014 1200z to 19/07/2014

 

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FORECAST
 
Synopsis

Long-wave trough extending south to west of British Isles and into Iberia remains slow-moving whilst becoming increasingly aligned NW-SE (negatively tilted). A strengthening southerly flow continues to transport, warm, moist and unstable flow north across British Isles. A thundery trough in the upper S'erly flow, that brought morning storms, will continue NE across northern Britain reaching N Scotland by midnight. Another thundery low developing over N France Friday PM will move N into S England by midnight, before spreading north across Midlands and Wales Sat morning.

 

... MDT RISK FOR S ENGLAND, E WALES, MIDLANDS, E ANGLIA ...

 

Plume of very warm and dry air at 850mb, evident on 12z Bordeaux and Trappes (Paris) radiosonde ascents above hot but moist surface airmass advecting north is providing a strong cap (lid) to convection this afternoon across France, though 850mb plume is creating steep lapse rates which combined with high temps approaching the mid 30s degrees C, is likely to yield MLCAPE of 1500-2000 j/kg. Cooling of mid-upper level temps with approach of upper trough to the west and convergence over N and W France is forecast to erode this cap Friday evening.

 

Model forecasts indicate thunderstorms breaking out this evening across N/W France, already there are storms across W France, which will then track north towards S England tonight. A strengthening southerly jet stream moving up from France and low-to mid level flow backing more SE'erly, as shown on Bordeaux and Trappes ascents, will increase vertical shear - allowing storms to organise upscale into an MCS, which may exhibit bowing line segments on its forward side, bringing the risk of damaging wind gusts, and also one or two supercells could be embedded. Large amounts of MLCAPE and strong directional shear shown by GFS suggests threat of large hail. The storm system moving north across the above areas tonight/Sat morning is also likely to produce frequent cloud-to-ground lightning. PWAT (precipitable water) values of 39mm indicated by GFS are very high- so excessive rainfall and flash flooding are a real threat too. Given the likely organisation of an MCS bringing widespread threat of wind damage, large hail and flash flooding - have issued a MODERATE risk of severe storms.

 

The situation will be monitored, given storms have still yet to form, with updates possible to the categorical risk of severe weather.

 

... IRELAND/N IRELAND, N ENGLAND and S SCOTLAND ...

 

Isolated storms may continue to occur this afternoon and evening, bringing risk of hail, gusty winds and torrential rain leading to localised flooding. Further storms are likely to reach N England from the south Saturday morning, with risk of hail, frequent cloud to ground lightning, strong wind gusts and localised flooding.

 

 

Issued by: Nick Finnis
Edited by Nick F

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Wrong thread

Edited by The PIT

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Its worth mentioning that the GFS picked up on the "mothership" now affecting the SE,whereas

the high res models didn't.

 

gfs.. euro4..

 

nmm..

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Saturday looks potentially interesting once detritus from overnight storms clears north. Should the atmopshere recover sufficiently with some sunshine, GFS depicts large amounts of CAPE building in the afternoon in the still very warm and moist airmass as temps rise towards high 20s deg C.

 

post-1052-0-43608700-1405722700_thumb.pn

 

Further storms, this time home grown, should, in theory, initiate along/ahead of the frontal zone running up through central parts early afternoon plus storms may form away from here along old outflow boundaries produced by overnight storms/MCS,

 

post-1052-0-61055700-1405722868_thumb.pn

 

We still have a strong mid to upper southerly jet and winds backed SE towards the surface - which will generate strong vertical shear. So storms that do develop, will quickly organise into muticell and even supercell structures given large CAPE too. So there is a risk of large hail and damaging wind gusts descending to the surface in downdrafts.

 

post-1052-0-62177900-1405723049_thumb.pnpost-1052-0-80416000-1405723083_thumb.pn

 

With surface flow backed SE'erly east of frontal zone and possible outflow boundaries also interacting, there seems a higher potential for tornadoes tomorrow, should storms be surface-based, lightning wizard shows the potential with its tornado parameters:

 

post-1052-0-81319000-1405723268_thumb.pn

 

Capping inversion in wake of overnight storms will likely be quite strong though, but if can be overcome, there's a lot energy to tap into! So strong to severe storms will be likely.

 

We may also import further storms from France, especially SE England, Sat evening/night.

Edited by Nick F

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Hmm, lot of detritus to get rid of this morning, with more thundery rain spreading up from France. Difficult to do a forecast for today given the blanket of mid-level cloud and rain lingering, because if it does break to allow sunshine, temperatures will rocket and the humid airmass will become very unstable across SE, central and E England ahead of the cold front moving in across western areas. GFS shows insane amounts of energy 1500 j/kg+ this afternoon. Vertical shear will be sufficiently strong for supercells producing large hail, damaging wind gusts and also a risk of a tornado:

 

Posted ImagePosted ImagePosted Image

 

However, worried that this cloud cover may take to long to clear to allow this kind of instability and thus potential for severe storms to be realised. We will see ...

Edited by Nick F

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Storm & Convective Forecast

 

post-1052-0-76824000-1405758471_thumb.pn

 

Issued 2014-07-19 08:25:26

Valid: 19/07/14 0900z to 20/07/14 0600z
 
THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FORECAST
 
Synopsis

Long-wave trough just west of western Europe continues to slowly advance eastward today, southerly mid-upper jet streak continues across France and British Isles ahead of this advancing trough, with a plume of warm moist air continuing to advect north, though beginning to be displaced east later in the day. A slack area of surface low pressure covers the UK, with a frontal zone lying SW Scotland down to Dorset at 12z (noon), with a warm/moist surface airmass that will be very unstable to surface heating to the east of frontal zone.

 

… ENGLAND and WALES …

 

Overnight storms will continue to spread north across England and Wales this morning, with further elevated storms moving north out N France in next few hours. Dependent on insolation breaking through cloud cover from morning convection later, any surface heating will allow temperatures to soar to the mid or upper 20s deg C this afternoon across S England. Combine this with dew points of 19-20C (already 19C observed in the SE) – large amounts of CAPE are indicated by models. GFS shows up to 1600 j/kg MLCAPE and up to 2000 j/kg SBCAPE this afternoon across SE England.

 

Breeze convergence ahead/near frontal zone and large scale ascent of airmass with approaching upper trough will likely erode any CINH/cap in place this morning, to allow storms to develop should surface heating take place. Strong mid to upper southerly jet and winds backed SE towards the surface will generate sufficiently strong vertical shear for any storms that develop to quickly organise into muticell and even supercell structures given large CAPE too. Such storms may produce large hail and damaging wind gusts.

 

Given potential for surface-based storms, any old outflow boundaries from morning storms and influence of backed winds near convergence zones, areas of strong low-level shear may develop – which may be sufficient for rotating mesocyclones on supercells that develop – which may produce one or two tornadoes too.

 

Therefore, have issued a Moderate risk across southern, central and eastern England – where surface heating is most likely and thus risk of severe thunderstorms.

 

… SCOTLAND …

 

Thunderstorms will continue to affect eastern Scotland this morning, with further storms pushing up from England or developing across more central and western areas during the day. Storms may produce hail, torrential rain leading to flash flooding and gusty winds.

 

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

Edited by Nick F

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The detritus is really annoying. And there is a fair amount of it to get through for the bulk of the country before potent home grown storms can develop. There is clear air to the west - and we can see storms developing over the CI's as a result. Also thinning in Lincs area going by this run. A waiting game!

 

http://www.yr.no/satellitt/europa_animasjon.html

Edited by chionomaniac

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Thanks as ever Nick, already seen some patches of blue.

After the storms the humidity is again soaring, extremely oppressive is really not an understatement.

Happy storm hunting campers.

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 Tricky to forecast today, not least because there is a lot of cloud around to subdue convection and I don't see it clearing much. So this will not really be any sort of forecast but more a discussion about ideas.

post-2809-0-77399800-1405762265_thumb.pn

 

The current satellite picture is interesting. Firstly I noticed an overshooting top in the MCS over the north sea. It kind of reminds me of an MCS which crossed Mallorca I think back 2007 which produced a weak tornado. 

Next I notice the orientation of the frontal zone which I think is more slanted than models would suggest, and seems to perhaps have a trough ahead of it.

There also appears to be an area where the frontal area is a bit broken over north France.

 

post-2809-0-22805300-1405762832_thumb.pn

 

That break in the frontal zone does sort of show up in modelling. For instance as perhaps drier air aloft.

post-2809-0-08657500-1405762939_thumb.pn

 

It also sort of shows up at lower levels creating a sort of weak surface low and a bit of a low level jet under it. Then perhaps it is me just paying too much attention to the models and reading things that are not there.

post-2809-0-35083400-1405763049_thumb.pn

 

I guess many will be reading this and wondering what I am blathering about and want me to spell out why this stuff interests me.  Low level jets mean vorticity which with a strongly unstable environment can be lifted to form a tornado. Drier air aloft enhances convection. So if the cloud does begin to clear and the modelling has some semblance of reality then there might be a short window of opportunity for a severe storm.  Judging by the way the models have struggled with this scenario, its more of an interesting discussion point rather than any real potential.

 

Leaving that aside I was also interested in the following lightning wizard chart.

post-2809-0-37309000-1405763510_thumb.pn

 

This would suggest to me that there might be potential for some sizable hail.

NMM suggests precipitation will likely be as follows during the afternoon.

 

post-2809-0-55214700-1405763594_thumb.pnpost-2809-0-96517500-1405763598_thumb.pn

post-2809-0-57533000-1405763606_thumb.pn

 

Broadly speaking I think is suggesting convection in the right areas, although I can already see some divergence between the modelling and reality already, so a large pinch of salt is required for anything discussed or shown above. There is a very real risk that nobody will see a storm across the UK today, although I am kind of thinking otherwise. We might have to wait until late afternoon (which might favour the north midlands northwards) and you cannot rule out the shear raw potential towards east Anglia. I am still kind of wondering what to make of that potential low level jet though and whether it coincides with other factors. Perhaps somebody else might like to pick up and discuss some of these features.

 

 

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Can someone here give me a technical explanation on what happened to the "Mothership" storm last night?

 

Basically it disintegrated once it was North of London.  Prior to that it looked as though it was steamrollering it's way North, the it seemed to hit a brick wall.  I'd like to understand what that was.

 

Thanks

 

There are a series of screenshots below

 

First one 19:55, going great guns in the channel heading for Brighton

 

post-9318-0-91095000-1405781779_thumb.pn

 

Then 20:55, on land heading for London, still big echoes, prhaps losing a little strength

 

post-9318-0-05479600-1405781819_thumb.pn

 

21:50, starting to look ragged as it hits North Essex

 

post-9318-0-74297800-1405781840_thumb.pn

 

22:50 weakening all the time

 

post-9318-0-62544900-1405781863_thumb.pn

 

23:50  --  Going backwards!!  moved 50 miles South compared to an hour ago

 

post-9318-0-37131400-1405781908_thumb.pn

Edited by NorthNorfolkWeather

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Would suggest that the severe storm complex in northern France as of present time (1730z) likely to impact east Sussex and most of Kent, may or may not brush southeast London and parts of Essex but most likely track and timing for severe storms would be something like Horsham to Rochester 8 to 11 p.m. ... Hail and intense lightning, local downpours, only slight risk of strong wind gusts.

 

 

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Can someone here give me a technical explanation on what happened to the "Mothership" storm last night?

Storms require heat and moisture to keep them going. When the storm moved out over the sea one ingredient was removed, namely high temperatures. Because the storm moved across overnight, temperatures were beginning to dip and may not have been high enough to get deep convection initiated to reinvigorate the storm. In this particular case I think there was an additional parameter in that upper level winds and temperatures were not quite as conducive for storms over the UK as over France earlier.

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