Uk Convective General Discussion & Forecasts - May 2012 Part 3

[Hammer]

Looks like already a little bit of activity near Basingstoke?

[fromey]

Looks like already a little bit of activity near Basingstoke?

dam you beat me to it! anybody down that way can confirm this?

fromey

[Carl46Wrexham]

Looking good for central London it may seem, London CIty TAF going for 40% prob heavy thunderstorm in hail, rain showers. With everywhere else PROB30

I was thinking could it be due to the fact the difference in temperatures/contrast between the different airmasses, being pretty much the same.... compared to a few years ago when say a cold front coming through was a proper strong cold airmass.

Decent shout.

[Methuselah]

In truth it would not surprise me in the least if the favoured spots get everything again, not just today but through to Wednesday, with the rest of us scratching our heads going "storms? what storms?"

There has definately been a pronounced shift eastwards with regards to where thundery weather occurs. I have not yet

heard or read a satisfactory explanation as to why things have so markedly changed in recent years. Why it is now that in Western Britain that thunderstorms are now an extremely rare phenomenon. I know and accept they occur more in the east naturally, but this does not explain the complete lack of storms in large parts of the West in the past few years.

The only 'explanation' I can think of is that, in recent summers, most of our heat has come courtesy of HP to the SE; this has pumped stable air masses across the UK whilst keeping the 'door' from the S and SE firmly closed. Hopefully, this summer will see HPs migrate more towards Scandinavia, allowing instability a chance to move N and W...Of course, this explanation might be cobblers!

[Supacell]

Thanks Coast, i always await your chart summaries before deciding on chase locations. From the charts it looks as though areas over London and immediately north and east are best placed today.

But for me that is a distance to travel, and there looks to be a further area of interest over the Pennines and then eastwards through the north Midlands and Lincolnshire this evening, which is much closer for me to travel to - but the met office precip doesn't seem to agree with this. And anyhow, activity unlikely to be as pronounced as the areas close to London. UHI effects may play a part here too.

I may take the plunge and swing down towards areas such as Bedfordshire/Cambridgeshire this afternoon.

[dallas]

Tuesday still on down here in the South maybe, but Wednesday looking active!

Coast would you by chance have a key for those symbols..............ta Edited May 28, 2012 by dallas

[Eskimo]

Coast would you by chance have a key for those symbols..............ta

The red is where thunderstorms are likely to occur, the green is rain and the little white circles are clear skies, the greyer the circles, the more cloud there is I believe.

[Cloudwatcher]

In truth it would not surprise me in the least if the favoured spots get everything again, not just today but through to Wednesday, with the rest of us scratching our heads going "storms? what storms?"

There has definately been a pronounced shift eastwards with regards to where thundery weather occurs. I have not yet

heard or read a satisfactory explanation as to why things have so markedly changed in recent years. Why it is now that in Western Britain that thunderstorms are now an extremely rare phenomenon. I know and accept they occur more in the east naturally, but this does not explain the complete lack of storms in large parts of the West in the past few years.

Yeah, taking the same view here in storm starved Ellesmere Port. Seeing the south-east getting all the action over the next few days unfortunately. Got the camera ready though, just in case

[dallas]

The red is where thunderstorms are likely to occur, the green is rain and the little white circles are clear skies, the greyer the circles, the more cloud there is I believe.

Cheers for that

[BrickFielder]

My first thought about today even without looking at the charts was that dewpoints were probably over done and surface temperatures under done. Now having looked at the forecast skewT's I don't think it makes much difference.

Forecast SkewT's are a forecast only though and you need to cross reference them with actual soundings and here we see some temperature inversions at 800hpa and 650hpa. This means that initially cloud will build at a low level until a certain temperatur is reached when it will build to 650hpa. A further rise in temperature will be required to get cloud building to the highest levels.

I also notice the instability on the actual reading (which I think will only be modified slightly during today) is more temperature dependant and instability is considerably weaker. What you should also notice is that lapse rates are rather week, which means air parcels will be slow to rise and hence storm clouds slow building. Watching the clouds yesterday in the west I saw how time ran out before the clouds could really start to build.

Storms tend to need a trigger and today I think the key is divergence at mid levels. 700hpa vertical velocity charts and mixed layer cape charts tend to confirm this.

This I think ties in with satelite cloud pictures where a band of cloud slowly moving east will destabilise during the day.

Spoilers for today would be slow cloud build and poor cloud top temperatures.

Slight instability just inland of eastern coasts where convergence zones set up at the surface could trigger an isolated weak tornado if the instability is realised.

Lapse rates steepen a little during the day and temperatures are likely to stay higher in the south east so perhaps around the London area will be key and the convergence zone north east of London late afternoon could play a part. Over all I think the storm risk is limited today but expect a few heavy showers trundling north west from London and Birmingham lat afternoon.

[VillagePlank]

[London/SE]

Still it's really not that unstable all the way up (K-Index < 26) Surface heating may not be good enough to get things going today, either,so we need another another trigger. We have a weak cold front passing in from the SW today,

But this really is quite a weak affair, so would suggest that local factors seriously come into play, today, such as orographic forcing. Areas associated with the cold front forcing air to rise are,

So, my guess today is that London and NNW/NW of London are best placed - Cambridge perhaps the sweet-spot - with the SE largely missing out, today. That's not to say that it won't, but the forecast isn't condusive to home grown storms in Kent/E Sussex. Perhaps N Kent coast might get a shot later in the afternoon - given it's propensity to post high temperatures (Gravesend etc) overcoming the relatively stable atmosphere.

Edited May 28, 2012 by Boar Wrinklestorm

[Eskimo]

Also as mentioned the UHI effect (Urban Heat Island) will play a role as well, even a couple of degrees higher in the city can have better effects.

[Sprites]

already convergence setting up through oxfordshire, and a few showers near oxford , may be altocumulus type at this ealy stage

[weatherobsuk]

A few nice clouds beginning to bubble up Buxton way. Going to head out now for a view across Cheshire so I should get a grandstand view of anything which forms across the Cheshire plain.

http://www.buxtonweather.fsnet.co.uk/buxtonview.jpg

[Mapantz]

BBC weather response on Twitter:- There is potential for enormous thunderstorms late today around the London area. Up to 30mm rain could bring localised flooding.

I hope some of you lucky folks in that area get something later. If you do .. get the pics and video up asap!

Edited May 28, 2012 by Mapantz

[Team Jo]

i Like the use of the word 'Enormous'

BBC Ramp!

[Supacell]

There looks to be convergence forming down the eastern side of the Pennines this afternoon coinciding with some decent CAPE. Could those driving on the M1 see a rush hour thunderstorm later this afternoon?

[Methuselah]

Nothing to report here, apart from some altocumulus way out southwest...

[swash]

looks like this one is on a knife edge. Met Office have updated their warnings for London/South East, but are saying that is is still unclear whether the storms will materialise or not

[VillagePlank]

Yes,

Interestingly enough, the yellow warning is *less* likely, but the impact is *higher* compared to yesterday. As the cold front moves in and measurements are made, I suspect that the little tick will go one box north warranting an amber warning.

Edited May 28, 2012 by Boar Wrinklestorm

[Methuselah]

looks like this one is on a knife edge. Met Office have updated their warnings for London/South East, but are saying that is is still unclear whether the storms will materialise or not

Very similar to last June's fiasco?

[VillagePlank]

You've got to give it to the MetO, though.

Just like forecasting snow, one parameter on a knife edge, and yet you are made to forecast, makes for one hell of a rollercoaster ride!

Things to think about today are

• Will it get hot enough - where?
  
• Will the cold front turn out to be more or less vigorous?
  
• What areas of the country are susceptible to orographic lift from the SW
  
• Are CZ forecasts accurate, what will heating do to change local wind patterns?
  
• Is there enough fuel to power a storm?
  

amongst a great deal of other things needed to take into account to get it spot on right.

Edited May 28, 2012 by Boar Wrinklestorm

[SnowJoke]

Altocumulus field to the SW of MK at the minute, appears to be the remnants of the decaying front, a lot of energy albeit capped at the minute as I can see shallow cumulus bubbling up and fading at a certain level along the old front

[tara303]

21 degrees here near heathrow, slight breeze, some altocumulus and haze to the east, i don't think perhaps, it will get hot enough to trigger anything off, trying reverse psychology lol........

[A.J]

hot, sunny & humid sums up the weather here in the West Midlands....There is some patchy Altocumulus overhead indicating some mid-level instability as a weakening CF encroaches from the SW...Also to my east, some convective cloud is bubbling up, but with a cap/inversion in place around the 850hpa mark, development is being inhibited currently....I think there is a lower risk of showers/thunderstorms for the west midlands today, but even so, I shall be sky/radar watching with interest