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Convective / Storm Discussion Thread - 31st May 2017 onwards


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2 hours ago, Dangerous55019 said:

Cheers for posting this @TJS1998Tom, and my thoughts exactly :)

Almost a week ago I posted up some very juicy looking charts that I cherry picked. Ever since then I've been watching these charts wax and waning, but the one thing that struck me was how consistent they were in going for a time round about that date... Give or take a day or so either way.
I also said 'that at two weeks away, what could possibly go wrong?'... Well here we are one week on and the charts seem to be getting even more juicy. :shok::bomb::yahoo:
Still an awful lot of water to go under the bridge as they say, but dare I say that we could be on the cusp of quite a memorable week for a lot of people? :bomb::friends:
Finger crossed for everyone who wants some storm action this coming week :friends:



*Memo to Self: Mustn't get too carried away, as I'm still receiving counselling for the last bout of heat when all we had was one poxy clap of thunder.* 

Well the 06z likes the idea of strong storms today for next week so who knows lol

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Popped out with the camera after finishing work yesterday at 5:45pm. Got onto the storm which passed through Malton when it was near Sledmere in the Yorkshire Wolds. Visually, it appeared supercellula

A few shots of the storm tonight using iLightningCam app.

BIG storm went over here earlier, only just got power back on. Trees down and roads flooded in the Malton area, never seen anything quite like it, absolute carnage. Unfortunately my weather stati

Posted Images

4774 j/Kg.. sarcastic_hand.gif

cape_132.thumb.jpg.f13ec6da966e0ff76572b300ac93ba3f.jpg

You can guarantee, that if it hasn't all disappeared, it would be around 1000 j/Kg on the day. The GFS always blows it out of proportion - best to look at extended skew-t charts, or soundings on the day.

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Don't forget that CAPE is all about that pesky theoretical parcel being warmer than the surrounding air at every atmopsheric level - CAPE of over 2,500 J/kg is considered extreme. In and of itself a forecast of high CAPE isn't necessarily an indicator of extreme weather, although, clearly, its very helpful as an indicator to look for other things; it's always worth remembering that this a theoretical value and it must be realised - worth looking at KI, and, perhaps, TT, to figure out whether it will be realised. In this case the KI on the skew-T above looks perhaps on the edge indicating a moderately convective environment.

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Echo all the comments above - hummana hummana 

Except the suggestion these charts are way over-egged. I'm not sure they are that over-egged - temperatures are expected to bounce back towards 30C on Thursday with high humidity - will just be a question of whether it can be released 

IMG_1138.PNG

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5 hours ago, Aqbadger said:

Out of interest anyone know the highest cape value recorded in the UK?

I studied this a few years ago and looked at the period 2002 - 2012. We ran WRF model simulations for those 10 years to examine the CAPE distribution spatially and temporally - the net result was the highest CAPE in that 10 year period in the UK was just over 3,000 J/kg. But this is reliant on a model, since getting actual measurements of CAPE is very difficult given how few vertical soundings are taken in the UK (twice a day at a handful of locations). The model itself can be configured various different ways, and this will ultimately have an impact on its calculation of CAPE. Nonetheless, it is quite likely the values currently suggested by the GFS will be toned down by the time we get to Thursday, as the model frequently over-exaggerates both hot and cold conditions in the medium range. That said, Thursday does look very interesting from a convective standpoint, and given the broad synoptic setup one should keep a keen eye on potential triggers that may tap into some of that instability.

You can read more about UK CAPE from the paper: http://onlinelibrary.wiley.com/doi/10.1002/joc.3976/abstract

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2 minutes ago, staplehurst said:

I studied this a few years ago and looked at the period 2002 - 2012. We ran WRF model simulations for those 10 years to examine the CAPE distribution spatially and temporally - the net result was the highest CAPE in that 10 year period in the UK was just over 3,000 J/kg. But this is reliant on a model, since getting actual measurements of CAPE is very difficult given how few vertical soundings are taken in the UK (twice a day at a handful of locations). The model itself can be configured various different ways, and this will ultimately have an impact on its calculation of CAPE. Nonetheless, it is quite likely the values currently suggested by the GFS will be toned down by the time we get to Thursday, as the model frequently over-exaggerates both hot and cold conditions in the medium range. That said, Thursday does look very interesting from a convective standpoint, and given the broad synoptic setup one should keep a keen eye on potential triggers that may tap into some of that instability.

You can read more about UK CAPE from the paper: http://onlinelibrary.wiley.com/doi/10.1002/joc.3976/abstract

Aye throw haze or thin clouds in that scenario you're buggerd  ,cape isn't everything ,lol

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Day 2 Convective Outlook

VALID 06:00 UTC Sun 18 Jun 2017 - 05:59 UTC Mon 19 Jun 2017

ISSUED 20:14 UTC Sat 17 Jun 2017

ISSUED BY: Dan

Under broad upper ridging on Sunday, strong surface heating will yield SBCAPE values of up to 1,000 Jkg-1 with dewpoints typically in the high teens Celsius. Forecast profiles are very dry, but given some sea breeze convergence one or two isolated heavy showers / thunderstorms may develop in the very late afternoon into evening hours (only 10-20% chance in any given location). Main risk will be local flash flooding given slow storm motion and PWAT of 30-35mm, suggesting 30-40mm may fall in a short space of time.

High-res models naturally vary with location of such showers, so not to be taken literally - however, general trend appears to favour Norfolk in particular, along a NE-SW convergence zone between Norfolk and London. There are also hints of a separate convergence zone from Lincs SW-wards to E Wales, though with less of a suggestion for showers to develop here - but may require a westwards extension to the LOW threat level if trends continue.

http://convectiveweather.co.uk/forecast.php?date=2017-06-18

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I am watching monday afternoon for some interest/action for areas from NE yorkshire to SW Wales with cape/li values of -3/-4 maybe touching -5 in the far east,the gfs in particular has been modeling a line of ppn in these said areas that i have mentioned above for days now,some other models do show showers dotted around these areas as well as cape/li,as for the rest of the week i am not going to put anything with confidence just yet but the potential is there,keep that heat coming and then i/we hope things go :bomb::D

cheers:drunk:

 

Edited by Allseasons-si
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It looks like I am going to miss out on the action this time around if anything does happen as most of the CAPE seems to be well east of here, with only a small amount showing for us on Monday or Tuesday.

Must bear in mind also that CAPE isn't everything and the models are probably showing it to be way overdone!:rofl:

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4 minutes ago, wimblettben said:

It looks like I am going to miss out on the action this time around if anything does happen as most of the CAPE seems to be well east of here, with only a small amount showing for us on Monday or Tuesday.

Must bear in mind also that CAPE isn't everything and the models are probably showing it to be way overdone!:rofl:

That is true Ben,just need the other factors to play ball

There does seem to be some CZ's from the midlands pushing south from 15:00-18:00 hrs

ukwind.pngukwind.png

maybe i will head south monday afternoon after work,finish at 2pm:)

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3 hours ago, wimblettben said:

It looks like I am going to miss out on the action this time around if anything does happen as most of the CAPE seems to be well east of here, with only a small amount showing for us on Monday or Tuesday.

Must bear in mind also that CAPE isn't everything and the models are probably showing it to be way overdone!:rofl:

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

Yeah, lol 2897j/kg for Thusday afternoon in Salisbury.. BOOM. 
Some of the maps don't gel with local stats from what I'm seeing, but where the is cape shown, it looks optimistic at least!
Saying that, think its fair to say that it's looking like the energy will be there for most central southern and eastern parts at some point regardless of cherry picked stats or charts, see how things go tomorrow eve and how models look.

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From UKWW:

 

Quote

Slight Risk of Isolated Thunderstorms E Anglia 15z-21z

Brief Synop;

Upper troughing influence negligible. Strong upper ridging sits just SE of UK and continues to influence north of this zone. Anti cyclonic upper jet arcs through Scotland. Low pressure to NW impresses surface boundary southwards PM.

Discussion; 

Today outlook could just as easily bust. Similar outlooks with strong upper ridging have in the past, .......on many occasions. Forecast shows some 'now' marginal risk where the low pressure slowly influences southwards. This is indicated by the slow turn of mid level vector from anti cyclonically to neutral. 

The contrast in potentially high surface temps to relatively cooler seas to the SE suggests a strong sea breeze convergence zone should develop through the afternoon, orientation SW to NE. It is along this line that surface dynamic lift will be strongest. So in short convection could potentially develop despite any weaker lifting components aloft. The prime risk today if convection can occur will be CG's and small hail. Storms if any) look to move SW to NE at around 20kts which should avoid cold pooling at surface. A significant condition will exist called 'Potential Instability'. In fact this condition looks to be absolute with dry air down as low as 700mb which is the optimum level for results. So whilst thermally the upper lapse rates are weak. This could be compensated by the effects of cooling dry air on any rising parcel. 

I cannot rule out a brief funnel where LCL is lowered near the zones of moist convergence. Though in general cloud bases look fairly elevated to 4,000 ft. Cloud tops potentially to 34,000 ft. Though this level looks to be a tall order based on the very dry zone up to to this layer.

 

Seems to be unlikely this side of London 

:sorry:

Edited by Flash bang flash bang etc
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3 minutes ago, Flash bang flash bang etc said:

From UKWW:

 

How do people know all this stuff??

Skew diagrams, the conditions above the boundary layer, pressure, surface temp and any convergence zones they think will happen. This is what makes storms so hard to forecast! So many ingredients to take into account. 

I wouldn't rule it out either. June 13th 2014 had some very impressive storms if you remember that affected the Home Counties and down to the south coast under a fairly robust high pressure, and moved southwards, and actually made it all the way to France as English exports! So anything is possible. As said, they would look very impressive and could well be observed from miles away given the height they could get to (34,000 feet). 

We shall see. 

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