Convective Storm/Discussion thread - 11/06/16 onwards

[Ben Sainsbury]

45 minutes ago, William Grimsley said:

I thought you were in Torquay?

Because of this "NCS" trip that I've done I was in Torquay from Last Friday to yesterday and bath uni from today till Sunday! Confusing lol!

[Nick F]

Storm & Convective Forecast

Issued 2016-06-22 08:00:56

Valid: 22/06/2016 06z to 24/06/2016 06z

DAYS 1 and 2 CONVECTIVE FORECASTS - 22/23 JUNE 2016

Synopsis

Amplifying long wave upper trough to the west of British Isles extends SE toward Portugal on Wednesday while flow becomes increasingly backed ahead of the upper trough across Iberia, France and UK ... this allows increasingly warm and dry air aloft (850-500mb) to be drawn north from Iberia and N Africa atop of an increasingly warm moist surface plume spreading north from France which will create an increasingly unstable airmass to develop and push NE across SE UK later on Wednesday and through Thursday. Increasingly strong SWly flow aloft and increased forcing for ascent of this unstable plume with engagement of upper trough is forecast to produce thunderstorms across parts of SE England and E Anglia late Wednesday onwards through to Friday ... some of these storms may produce severe weather.

DAY 1 CONVECTIVE FORECAST – WEDS 22-JUNE-2016

Valid 22/06/16 06z to 23/06/16 06z

... SE ENGLAND and E ANGLIA ...

An Elevated Mixed Layer (EML) plume, consisting of warm dry layers and characterised by steep mid-level lapse rates, will continue to advect N/NE from Iberian Plateau/N Africa towards Sern England over next 24hrs atop of increasingly warm and moist boundary layer airmass spreading NE from N/W France. 

GFS does build several 100 j/kg CAPE across SE England, E Midlands and E Anglia, but slow-moving frontal boundary from SW England to Lincs producing extensive cloud cover/rainfall will hinder surface heating and poor lapse rates suggest the risk of thunderstorms is low, though a few heavy perhaps thundery showers developing along breeze convergence towards E Anglia and Lincolnshire coastal areas can’t be ruled out.

The main thunderstorm potential in the next 24hrs develops from the south later today. Models indicate over France today very strong surface heating (temps of 30-35C) of humid airmass (dew points 20c+) - which beneath steep lapse rates of EML will allow strong instability to develop (1500-2000 j/kg) CAPE. Increased forcing for ascent of this hot and humid airmass from approaching upper trough and subtle shortwave troughs running NE in strong SWly flow aloft combined with surface convergence is indicated to trigger strong thunderstorms across northern France in the afternoon/evening. Given strong instability combined with strengthening and veering of mid-upper flow as upper trough sharpens out west, storms here may develop supercell characteristics and produce all severe hazards before growing upscale into a MCS and other storm clusters that could affect parts of SE England and E Anglia late evening and overnight period as they continue to track NE. These storms will probably be mainly elevated once they’ve crossed the English Channel, posing predominantly a risk of locally severe wind gusts and a widespread risk of excessive rainfall leading to flooding. Therefore have issued a SLIGHT risk of severe weather. Frequent cloud-to-ground lightning and hail will be an additional hazard with such storms.

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DAY 2 CONVECTIVE FORECAST – THURS 23-JUNE-2016

Valid 23/06/16 06z to 24/06/16 06z

… S ENGLAND, E MIDLANDS, LINCS and E ANGLIA …

UKMO fax charts indicate slow-moving cold front will lie SW-NE from Weymouth to The Wash midday Thursday, ahead of this front – a warm/humid airmass characterised  by dew points of 16-18C / PWAT values of 1.2/ - 1.6 inches. Thunderstorms are likely to be ongoing Thursday morning across parts of SE England and E Anglia from overnight storm clusters /MCS moving NE from France … residual cloud cover from these storms may tend to inhibit surface instability … but eventual cloud breaks will allow instability to rebuild as surface heating of humid airmass increases. GFS indicates 500-1200 j/kg CAPE across the above areas in the afternoon/early evening. Thunderstorms are indicated to redevelop as surface heating combines with approaching upper trough and surface convergence ahead of cold front to create forced ascent of humid airmass. Storms will form in an environment of veering and strengthening flow aloft that will be characterised by 40-50 knots of deep layer shear, so storms will likely organise quickly … initially a few supercells or bowing line segments are possible … though unidirectional winds aloft will tend to line out storms. Nonetheless, all severe weather hazards are possible from storms  … mainly the risk of isolated large hail (2-3cm diameter), damaging wind gusts, flash-flooding and perhaps even a brief tornado where winds back SEly and increase SREH (Storm relative helicity). Given uncertainty of how widespread storm development will be, storms maybe isolated, have issued a SLIGHT risk of severe weather for now, though upgrade to MDT in later updates.

… EIRE/N. IRELAND and SCOTLAND …

Atlantic upper trough axis moves in across Ireland and W Scotland on Thursday, associated cold mid-level temperatures will create steep lapse rates atop moist maritime surface airmass, with surface heating creating 200-500 j/kg CAPE in the afternoon – so scattered heavy showers and a few thunderstorms look likely to develop across the above areas. A few organised storms can’t be ruled out … producing a risk of hail, flash flooding and gusty winds locally … though modest instability and shear will limit severe risk.

Issued by: Nick Finnis

[William Grimsley]

@Nick F, basically good luck to those in the SE, looks frightening!

[William Grimsley]

2 minutes ago, Ben Sainsbury said:

Because of this "NCS" trip that I've done I was in Torquay from Last Friday to yesterday and bath uni from today till Sunday! Confusing lol!

NCS? I remember that being advertised at school, seemed legit not... Anyway, back on topic...

[East_England_Stormchaser91]

11 minutes ago, William Grimsley said:

I have to agree with W09, here. Where have you got this from? Just looks like some mashed up rubbish to me.

I can see where mesoscale is coming from entirely myself. I've lost count of how many times I've seen the real fun and games only unfold the other side of the channel when we have been forecast storms in this setup. Pretty much the whole time between 2007 and 2012 we saw nothing and the likes of Benelux hit gold. Only the last few years have we got very lucky on some occasions. 

The forecast to me clearly implies only a slight possibility that we may see some proper fun. If I could get the train to somewhere like Lille in the next 24 hours over staying in Kent, I'd be over there in a heartbeat. The steering winds to me look unfavourable, and would favour a big eastward shift as the event unfolds. 

Would not be at all surprised if we only see a usual Kent clipper scenario. Sorry to come across as a pessimist myself and a bit conservative of the forecast later, but it would be wishing on a triumph of hope over experience to think that we are going to be slammed by MCS of the decade. I've watched ad nauseum now the amount of times we've been disappointed over this type of setup! 

[Azazel]

4 minutes ago, William Grimsley said:

Oh, Azazel, unfortunately I don't agree with your statement, there is no such thing as "We've seen this so many times in recent summers". It doesn't matter what Summer we're in, it's just that recently parameters have not been good enough to sustain MCS development over the UK, nothing to do with the year, it's to do with that. I have good confidence that at least thunderstorms with a certain degree of MCS development will move across Kent this evening, there's already thunderstorms in France so will be quite interesting to see what happens later.

I admire your optimism William and I for one hope that I am wrong! Would love to see some storms.

 

I have to disagree though, we have had the ingredients in place several times since 2006 and the goods have failed to deliver with MCS clusters seemingly preferring to hug the North France coast into Belgium/Holland.

Like I said though, hopefully I'm very wrong and storms fire a lot further west than currently progged.

[William Grimsley]

You can agree or disagree, that's your opinion but I certainly think that just because we are an island and that "something" has changed our risk is utter rubbish.

[Azazel]

Looking at the charts for tomorrow, if anything fires, i'm thinking maybe a squall-like feature for the red box. Yellow box is where i would expect convection to fire if the cloud breaks and surface-heating occurs. This is for tomorrow PM...NOT for tonight.

Edited June 22, 2016 by Azazel
edit due to misunderstanding.

[weather09]

So we've gone from confident of storms only clipping the SE, to squall line over east Anglia. Lets cover all bases so one can't be wrong.

And since when did what happened several years ago have any bearing whatsoever on what's going to happen this evening and into tomorrow?

BS.

[Harry]

14 minutes ago, East_England_Stormchaser91 said:

I can see where mesoscale is coming from entirely myself. I've lost count of how many times I've seen the real fun and games only unfold the other side of the channel when we have been forecast storms in this setup. Pretty much the whole time between 2007 and 2012 we saw nothing and the likes of Benelux hit gold. Only the last few years have we got very lucky on some occasions. 

The forecast to me clearly implies only a slight possibility that we may see some proper fun. If I could get the train to somewhere like Lille in the next 24 hours over staying in Kent, I'd be over there in a heartbeat. The steering winds to me look unfavourable, and would favour a big eastward shift as the event unfolds. 

Would not be at all surprised if we only see a usual Kent clipper scenario. Sorry to come across as a pessimist myself and a bit conservative of the forecast later, but it would be wishing on a triumph of hope over experience to think that we are going to be slammed by MCS of the decade. I've watched ad nauseum now the amount of times we've been disappointed over this type of setup! 

This statement is perhaps misleading. Unlike ConvectiveWeatherUK's forecast zones which forecast first and foremost probability, Nick F's forecast zones focus on severity. The 'slight' does not suggest slight chance of thunderstorms (far from it) rather that thunderstorms in this area are predicted but with a 'slight' chance they will be severe. 

To save me having to create my own chart, I happen to fall closer in line with Dan's projections on convectiveweather.co.uk, slightly more east favouring than Nick F's (which I do not like saying as it leaves my chances lower than under Nick's forecasted scenario). I would clarify both Dan and Nick are substantially more knowledgeable and qualified than me, but taking all of the trusted models together and drawing a median, Dan's is the best fit in my opinion.

As a Man of Kent born and bread, I am rather qualified in evaluating the outcomes of plume forecasts vs actual events, and generally speaking in setups like this thunderstorms occur more often than not. Models have routinely been projecting the advection of highly unstable air across the SE and continue to do so. On this basis, I think thunderstorms are likely, but what is open to question is where the triggering trough will actually sit and thereafter where thunderstorms, which will trigger throughout the night, will train. 

[A.J]

I think a lot of people's views that there have been a lack of plume type scenarios is from an IMBY perspective which can muddle reality......over the past few summers there have been plenty of destabilizing plume scenarios, but with the fickle nature of thunderstorm forecasting just because one is slap bang in the middle of a forecasted warning one does not guarantee that one will actually experience a storm....In fact, I think the past 2 or 3 summers have been good for plume scenarios as when they've occurred the main storm motion has been south to north with WAA from Iberia affecting more parts of the UK than summers previous....tonight/tomorrow's scenario looks more like the plume scenario's from a few summers back with more of a sw-ne axis of movement leading to fewer parts of the UK being affected

[MP-R]

The reason I'm not excited about this event is because the whole pattern is happening too far east. This would be a great set up if the trough moving up from the south was coming up to the south/southwest rather than the southeast. I think this bares similarities to 06th August 2008 does it not? The southeast got a wonderful show then, right on the northwest tip of a tongue of warm air; the rest of the country however did not. I would say the southeast is in with a good chance of seeing something at least half decent but in the wider picture, there is nothing very exciting about this particular event.

[Azazel]

4 minutes ago, weather09 said:

So we've gone from confident of storms only clipping the SE, to squall line over east Anglia. Lets cover all bases so one can't be wrong.

And since when did what happened several years ago have any bearing whatsoever on what's going to happen this evening and into tomorrow?

BS.

two different time periods mate.

Storms POSSIBLY clipping the SE is for tonight, squall line POSSIBLY over East Anglia is for tomorrow PM.

its called looking for patterns. If you disagree that there has been a propensity for MCS to affect the Benelux countries in recent years rather than engulf the UK then that's your opinion, which is at odds with the facts.

[Harry]

Just now, Azazel said:

two different time periods mate.

Storms POSSIBLY clipping the SE is for tonight, squall line POSSIBLY over East Anglia is for tomorrow PM.

its called looking for patterns. If you disagree that there has been a propensity for MCS to affect the Benelux countries in recent years rather than engulf the UK then that's your opinion, which is at odds with the facts.

Of course MCS have been more frequent over Benelux in the past few years...that is not to say when conditions have been favourable here that Benelux have stolen them. 

[A.J]

1 minute ago, Azazel said:

two different time periods mate.

Storms POSSIBLY clipping the SE is for tonight, squall line POSSIBLY over East Anglia is for tomorrow PM.

its called looking for patterns. If you disagree that there has been a propensity for MCS to affect the Benelux countries in recent years rather than engulf the UK then that's your opinion, which is at odds with the facts.

can you supply a source for these facts Azazel?.....I simply ask because your post is at odds with what I've read in storm threads on Netweather over the past 11 years 

[weather09]

Ah right, didn't know there was a risk for tomorrow.  Only been mentioning for the last few days. Appears my posts have gone into the void again

And it's not about patterns, it's about looking at the period at hand and not have your thinking influenced by what has happened in the past. Just because there have been occasions when storms have missed the UK, doesn't mean storms will keep missing the UK.

[Azazel]

I dont mean Benelux have stolen them physically haha, i mean due to the steering flow MCS that are often forecast to affect more of the South/South East very often travel more North-Easterly than expected and across the Benelux Countries or up the north-sea.

Maybe stating it as fact was a little strong and i apologise, however it is my strong opinion that in these type of setups, we will usually miss out.

[Martin Auld]

I had this MCS in the early hours of July 2nd 2015 seems like the same thing might happen tonight in the south east of England so good luck to anyone down there it could be quite the spectacle

[Azazel]

Anyway, sorry to double post. Lets get this back on topic.

 

I really hope we do see storms and i'm not trying to rubbish anyone else's opinion (if it came across that way, it wasnt my intention). We are all weather enthusiasts at the end of the day and the fact these debates/arguments occur is indicative of the passion we share.

I'm fed up with the lack of storms down in my neck of the woods over the last 10 years so maybe that's why I came across as a party-pooper. I didn't mean to and i apologise.

 

Fingers crossed for those in the South-East tonight and I hope you get something!

[William Grimsley]

Don't worry, Azazel we can all come over as being not what we want to be (especially myself).

Just looked at the latest NMM run, slightly worried if that pulls off both for potentially hitting home and the intensity of the rainfall across SE England.

Edited June 22, 2016 by William Grimsley

[NO LONGER POSTING]

Lots of crystal balls in this thread 

[Mapantz]

I suspect an amber warning will get issued for excessive rainfall for parts of the SE.

[Sussex Jules]

1 minute ago, Mapantz said:

I suspect an amber warning will get issued for excessive rainfall for parts of the SE.

Just been issued. Anyone got a boat handy?!

[Mapantz]

1 minute ago, Sussex Jules said:

Just been issued. Anyone got a boat handy?!

Ah - Just a few minutes ago..

 

[Lauren]

I don't think any one is imagining the lack of MCS storms over the years from the SE.

 

Certainly, Harry will back me up that during the 90's they used to be a fairly regular occurrence with them starting early evening and still rumbling away at dawn.