Storm & Convective Discussion - 16/07/15 onwards

[sunnijim]

Estofex and Nick F were certainly bang on the money. The BBC seemed to exaggerate lightning activity further north. But the risk was certainly there, and it is their duty to give a more broader outlook to Joe public, Estofex and forums like this go into the depth much more. I keep telling my family and mates exactly what the case is, but they still try and dispute by saying 'well my iphone says this' nonsense!

Bang on there! Bloody phone apps are the bugbear of our age when it comes to forecasts." My app says this or that" so that is what shoud happen! If not the

Weather forecasts are wrong.

"Look,my app says rain and i'm on the beach in sunshine!" How mad is that.

Give me strength.

[A.J]

I just checked my app....it said I was 3 stone overweight! 

 

 

anyhoos, heavy rain affecting parts of the west country, as an advancing cold front interacts with the remnants of the plume, and as posted in the regionals a short while ago, the cold front is slow moving so the possibilities of some flooding issues are there. It will be interesting to see if the cold front can act as forcing trigger for areas further east and aiding the development of a few storms in those areas

Edited August 14, 2015 by ajpoolshark

[Summer Sun]

Updated warnings from the met office

 

Issued at: 1031 on Fri 14 Aug 2015

Valid from: 1040 on Fri 14 Aug 2015

Valid to: 1800 on Fri 14 Aug 2015

 

Further heavy rain is expected across northern parts of England and fringing into parts of eastern Scotland - the rain gradually easing from the south. Be aware of the risk of localised disruption due to surface water flooding, with the greatest risk over northern England at first. This is an update to the existing Yellow Warning to reduce the area at risk, whilst a separate Yellow Warning will be issued for east and southeast England.

 

Chief Forecaster's assessment

 

An active frontal system lying from eastern Scotland to the West Country will continue to produce areas of heavy rain today, particularly across northern England. Hourly totals of 10-20 mm of rain are possible in places at first with localised 3 hourly totals reaching 35 mm - the rain easing from the south through the afternoon.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1439506800&regionName=uk

 

Issued at: 1042 on Fri 14 Aug 2015

Valid from: 1200 on Fri 14 Aug 2015

Valid to: 2000 on Fri 14 Aug 2015

 

Although many places will be dry, there is a risk of isolated thunderstorms breaking out across parts of east and southeast England this afternoon and early evening. Be aware of the risk of very localised surface water flooding.

 

Chief Forecaster's assessment

 

The cloud is expected to break to allow some sunshine this afternoon and as temperatures reach the low 20's Celsius, there is a risk that isolated thunderstorms will develop. Where thunderstorms do occur, 20-25 mm of rain could fall within an hour.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1439506800&regionName=uk

[BrickFielder]

  So we have a slight risk of storms today mainly towards East Anglia according to the models.

  There is however differences in the different modelling solutions, so again there has to be a large caveat on any forecast. I am again not entirely convinced the model output has totally got a handle on environment. Looking at the EuMetsat pictures I can see a lobe of vorticity over northern France which does not clearly show up on the model output. I don't think this lobe will come the UK's way but I think it may delay the eastward movement of the Front across the UK. My best guess at the moment would be that the low over France will weaken with perhaps a secondary weaker low center developing towards the UK. This I base on the movement of cloud to the north west of the low center. Any weak low development towards the UK could perhaps lead rise to a few surprise thunderstorms. I think because this is all hunch and guess work the probability of this should be close to zero percent.

  I personally find it interesting for a change not to be totally reliant on the modelling and to try to second guess what I think might be happening from the Satellite and rainfall radar images. This is when you get to test your understanding of the atmosphere  and to learn new things (second guessing sophisticated modelling invites failure). Getting things totally wrong is the best way to learn, so nobody should be ashamed of that and provided you are honest and admit your failings , then you will resist the temptation to be complacent in your knowledge.

  So I invite all budding forecasters to have a go. We will probably all be wrong today, so there is no pressure.

[Harry]

I am going to throw my two-penneth in without going into too much detail.

 

My view is the BBC over-egged the lightning symbols as it never really looked like being a widespread thundery outbreak - I posted to this effect a couple of days ago and it seemed to me that the consensus on this forum was much like mine - potential for some thunder, but limited in coverage. Instability, based solely both SBCAPE and MUCAPE, always look meagre at best  and largely confined to southern most areas - in such situations it helps to base expectations on this factor first and foremost, then look at whether the atmospheric profiles are conducive for detonation.

 

Yes, high CAPE does not always result in storms, and low forecast CAPE does not preclude storms, but generally the principle is there. I personally have felt that the BBC have been a little bit trigger happy with the lightning symbols on occasions this year, but hey ho they are professional forecasters, I certainly am not. Furthermore, there was fairly widepsread thunder activity across the SE yesterday, which is where it largely always looked most likely to be (much closer to the real instability over the continent). 

 

That said, it is irritating to fill this forum up with moans when there is a special thread for that...I am only highlighting it here to help members focus attention on the better sources (i.e NetW forecasters and CAPE charts, rather than BBC/ITV forecasts).

 

This afternoon could well be interesting, but again its a highly complex environment - a lot of cloud, despite recent breaks here in London and across other parts of the SE. Definitely humidity is up, but the cloud cover is again filling in. I would pitch any thunder risk afternoon at <20% for England generally, perhaps 30% across London and the Home Counties - possibly somewhere E or NE of London most favoured (say 35% chance).

[Flash Elvis]

  So we have a slight risk of storms today mainly towards East Anglia according to the models.

mlcape16.pngsbcape16.png

  There is however differences in the different modelling solutions, so again there has to be a large caveat on any forecast. I am again not entirely convinced the model output has totally got a handle on environment. Looking at the EuMetsat pictures I can see a lobe of vorticity over northern France which does not clearly show up on the model output. I don't think this lobe will come the UK's way but I think it may delay the eastward movement of the Front across the UK. My best guess at the moment would be that the low over France will weaken with perhaps a secondary weaker low center developing towards the UK. This I base on the movement of cloud to the north west of the low center. Any weak low development towards the UK could perhaps lead rise to a few surprise thunderstorms. I think because this is all hunch and guess work the probability of this should be close to zero percent.

eumetsatimage.png

  I personally find it interesting for a change not to be totally reliant on the modelling and to try to second guess what I think might be happening from the Satellite and rainfall radar images. This is when you get to test your understanding of the atmosphere  and to learn new things (second guessing sophisticated modelling invites failure). Getting things totally wrong is the best way to learn, so nobody should be ashamed of that and provided you are honest and admit your failings , then you will resist the temptation to be complacent in your knowledge.

  So I invite all budding forecasters to have a go. We will probably all be wrong today, so there is no pressure.

Excellent Post - you are right people shouldn't be worried about getting it wrong, we are all on here for our love of weather and everything that comes with it. 

 

I for one read everything on here and try to understand the complex things that happen in the atmosphere to improve my knowledge of the weather but filtering out all the moaning and back biting is just a chore.

[alexisj9]

Sun out here 

And here, cumulus moving in from the SW and not NE too which means the low has finally moved north.

[Rain123]

I personally think any storm activity will be across kent/east anglia, but then I have little knowledge compared to many of you on here. 

Also, no breaks in the cloud here. 

[NO LONGER POSTING]

Something is brewing EURO4 does have some interest but it is much later when the front moves east..

 

 

 

 

Looks like it wants something around the IOW to kick of and move North East.. 

Edited August 14, 2015 by Surrey

[weatherobsuk]

Flooding incidents in Manchester and surrounding areas..

 

The average rainfall for the entire month of August in Greater Manchester is usually 80mm.
The Met Office reported that in the last six hours, 30.8mm of rain fell at an observation station with a rain gauge based in Rochdale. That means that just under half of a normal August's rainfall has fallen in the last six hours.

 

http://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-rain-flooding-travel-live-9856044

[Chris.R]

Just approaching 15 mm here for the day, with 2.6 mm in the last hour. Steady rain all morning, getting a bit heavier now.

Edited August 14, 2015 by Chris R

[Tamara]

Chill.

 

And yet those very same people moan when they don't get their hot weather or snow, it's inevitable on a 'weather' forum,, you take the good with the bad.  As long as it doesn't get personal then I don't see the issue, I did however read alot of comments of people antaginising people who were dissapointmented in the lack of light show.

 

I think people need to lighten up, I certainly have a chuckle when reading people's comments as they chuck their toys out of the pram!  But we all have a common interest in the weather, lets focus on that.

I think it is largely the same type of people who moan - whether it is snow and/or cold in winter or heat and/or storms in summer. These combination types identified principally first and foremost - because they provide greatest spectacle stimulation and excitement over other weather types 

 

A weather forum is naturally populated by people who seek out the excitement and fascination of such weather types - but unfortunately preference and hope driven factors and the associated anticipation of favoured weather type occurring, overwhelm and override any potentially existing motivation to try and learn about and attempt to understand the background meteorological science that would, rationally and logically, help manage the expectations, hopes and chances about that weather type occuring in the first place.

 

An immature  "fast food - I want now" type approach to the subject rather than any intelligent motivation and curiosity to desire to, or want to, attempt to understand the complex mechanisms that underly the dynamic weather types provided by Mother Nature

 

Its no surprise that (relatively speaking) so few technical and summary posts appear in threads like this. I am not at all keen on storms in the same way as I would favour snowfall in winter, but still seek out technical summary threads from other knowledgeable and level headed posters about storm potential because whilst I don't like on a personal level the more severe storms especially right over my roof top, I am still interested and fascinated by them in the same way as the vastly wide aspects of synoptic weather forecasting, and the weather in general, interest me.

 

It definitely becomes an extra bonus attempting to learn about your favoured weather type(s) a) because individual subject matter is increased, and acquired knowledge is a valuable, personally satisfying and cost free asset that means b) your anticipation of weather events such as showcased on forums like these can be further heightened, increased and also contributed to others through having that knowledge and c) your individual expectations regarding it are managed better because that increased knowledge and understanding means that you can increasingly make better informed decisions personally in terms of how likely that particular sought after weather type is likely to verify.

 

These measured opinions can then be ploughed back into the thread(s) to help improve and manage expectations of others (who can be bothered to read them and try and benefit from them)

 

Such informed opinions/decisions may still go wrong and often do - the weather makes mugs of the best of us. However, managing expectations in a positive learning way means that there *should* be less "wrist slashing" and disappointment even if the best informed forecast suggestions do not verify according to plans

 

Sadly, the sheer number of moaning posts by those who cannot be bothered to further their understanding of the subject matter mean that the (relatively) fewer rational and informed posts (that serve to answer and combat the uncontrolled and immature angst of the fast food culture), go further unnoticed and unread onto a previous page amidst a fast moving sea of "will there be thunder" spam and childish tantrums because the As Cas cloud over *insert name of location* apparently refuses to discharge...

 

Opening specialist and technical threads has always been a solution, and deals precisely with much of the ill informed and childish disappointment-driven dross that fills up these pages, but such informative material largely gets unread and therefore the more technical posters "chance their arm" instead in the "will there be a storm/snow" type threads such as these.

 

Last, but by no means least in terms of any philosophical type of contribution such as this - to echo one or two other recent posts, there is more to life as to whether there is a storm or whether it snows (or whatever else the weather may throw at us) and there is a life to live completely away from a computer screen....

 

I would look at the current convective episode which has proved difficult to forecast accurately synoptically with interest from the same learning curve perspective as outlined above. 

 

There has been a dynamic boundary line actually for much of the whole summer over the UK between intense heat over much of mainland and central/southern Europe and cool moist Atlantic air overlain most especially across north western parts of the UK.

 

Looking at this weeks synoptics, this boundary line has been excellently illustrated and manifested as a cold front (initially at the start of the week) that attempted to come south east through the UK, but then got "stuck" over SE 'ern most parts over the the middle part of the week before returning north-westwards through southern England with associated humidity yesterday.

 

Based on the inertia lack of forcing of the cooler Atlantic air to the north west and the humid unstable air to the south and south east, then on a very micro level, the model calculations regarding the northern most extent of the theta plume, were always going to be particularly tricky.

 

More than usual tricky.

 

Its proved the case that the modelling has very slowly adjusted that stuck frontal boundary from just off the south east coast earlier in the week, some 40 miles, maybe, further northwest. Not much at really, but this has had the effect of skewing the surface pattern enough to considerably change the expected distribution break-out of middle level convection on the northern perimeter of the plume as had been expected mid week. 

 

Here, its worth bearing in mind just how often that the UK represents the northern most boundary of northward advecting theta plumes - and therefore calculating the speed, timing and geographical extent of destabilisation of the plume is going to be more difficult than further south over France/mainland Europe closer to the where the air-mass originated and areas which are more slowly/ less influenced by maritime Atlantic air-masses compared to the UK.

 

In this sense, percentage starting expectations of mid level instability storms occuring is quite sensible and not prove too far wrong. Gauging where surface instability might break out in plume situations is, I think, a fair bit harder to do than during polar maritime/returning polar maritime Atlantic type pulse natured convectional events which are dictated by surface heating vs upper low cold pools which steepen lapse rates and result exclusively in SBCAPE rather than MLCAPE and SBCAPE

 

Added to the mix is the fact that this has not been a classic type plume in terms of usual advancing Atlantic upper trough vs downstream ridge and associated Tropical Continental airmass destabilising in tandem with the cold front of the eastward moving trough. These, although still requiring some care, in relative terms, are "easier" to predict than what we have seen this week.

 

As described above, this whole week has featured a surface feature pattern revolving around a wriggling frontal boundary, within a mid latitude ridge, extending all the way back SW to Iberia. Effectively the heat low over Iberia spawning as the "secondary low" to move NE along that wriggling boundary - and modelling the micro movements of this low has been enough to make such obvious differences in the initial programme timings of the arrival of the associated theta plume and the spatial distribution of associated convective break-down over what is a very small area when taken from a hemispheric perspective. 

 

The straddling front throughout the week has generated stubborn cloud which was in place already when the humid air-mass starting edging back through southern England yesterday. This has further made problematic deciding where convection may occur, but with regard to SBCAPE convection which relies on surface heating. The "classic" plume more often that not features strong hot sunshine prior to storm destabilisation on southerly winds wafted up from southern Med and North Africa

 

Think that will do for the time being..

 

Edit: Brickfielder's recent post is a very good positive example of my long waffle

Edited August 14, 2015 by Tamara

[Condor Vitesse]

The way i see it is this..Do not slate anyone if they get it wrong but by all means you can think the sun shines out of ther @@@@ if they get it right.. . If you do not want people to act disappointed do not overhype the situation..

[NO LONGER POSTING]

Straw clutch but EURO4 may have something here..

 

[sunnijim]

Yup,storms fireing over Northern France now ahead of the cold front that has all but stalled over the West Country.

[NO LONGER POSTING]

Yup,storms fireing over Northern France now ahead of the cold front that has all but stalled over the West Country.

 

Yeah Just seen that also the PPN is really pepping up now..

 

Could this be the last straw clutch that pulls of 

 

Wouldn't mind betting that the stuff near Portsmouth goes up soon  

Edited August 14, 2015 by Surrey

[Dean E]

Straw clutch but EURO4 may have something here..

 

storms.jpg

 

Have noticed this too and there is rapid cloud formation within the front as seen on the last few Satellite runs

 

 

Lets see how this pans out

[Condor Vitesse]

The way i see it is this..Do not slate anyone if they get it wrong but by all means you can think the sun shines out of ther @@@@ if they get it right.. . If you do not want people to act disappointed do not overhype the situation..

By the way that was sarcasm and no way intended as an insult to the fine people on here. The Meto etc have to cover themselves as there would be even more complaints if no warnings were issued.

[NO LONGER POSTING]

Have noticed this too and there is rapid cloud formation within the front as seen on the last few Satellite runs

 

Capture.JPG

 

Lets see how this pans out

 

Every single model agrees on some hefty showers popping up this afternoon and evening they will be VERY slow moving as the flow is so slack.. 

[Rain123]

A slightly heavier band of rain moving very slowly in, the sky doesn't look very dark. Doesn't feel warm enough for any thunderstorms, so I think these will just be heavy showers. 

EDIT: Is heavy drizzle a thing. If it is, we have it now (1523)

Edited August 14, 2015 by Rain123

[Harry]

Every single model agrees on some hefty showers popping up this afternoon and evening they will be VERY slow moving as the flow is so slack.. 

 

Indeed....atmosphere just doesn't strike me as sufficiently conducive for thunder. 

 

Still a humid feel out there so certainly some moisture to wring out

[alexisj9]

A slightly heavier band of rain moving very slowly in, the sky doesn't look very dark. Doesn't feel warm enough for any thunderstorms, so I think these will just be heavy showers. 

EDIT: Is heavy drizzle a thing. If it is, we have it now (1523)

Yep get a load of it in coastal area's it's quite normal for here, most rain falls as heavy drizzle instead of moderate rain lol.

[alexisj9]

Indeed....atmosphere just doesn't strike me as sufficiently conducive for thunder. 

 

Still a humid feel out there so certainly some moisture to wring out

Feels like thunder here to be honest, been humid since god knows when, it didn't go before this lot arrived. and it's warm and sunny too.

[Rain123]

Yep get a load of it in coastal area's it's quite normal for here, most rain falls as heavy drizzle instead of moderate rain lol.

Oh, interesting.

[Summer Sun]

A 15ft wide by 40ft deep hole has appeared in Manchester following heavy rain

 

Edited August 14, 2015 by Summer Sun