Storm & Convective Discussion - 20th August 2015 onwards

[William Grimsley]

I appear to have been quite lucky this year with storms, having 7 thundery events that I have witnessed so far. The best storm I have witnessed in my life was July 2014. I can't remember what day it was,  but at one point there was lightning every 3-5 seconds! 

Yes, I had a similar lightning frequency in the thunderstorm in September 2014, here.

[MP-R]

Really shows how different synoptic setups favour different parts of the country. Here in winter, westerlies tend to bring the highest risk of thunder, normally from showers off the Severn Estuary. Into spring and summer, then the highest chance of thunderstorms comes from cyclonic southwesterlies, probably followed by rPm southeasterlies, then when plumes actually move north rather than northeastwards. The best storms used to be from plumes. During summer, we're often well placed for homegrown thunderstorms moving westwards. Northwesterlies also only tend to bring thunder here in the high months of the year. Into autumn and anywhere between south and west is the best direction.

 

It's quite amazing really that my location can favour from so many different setups re thunderstorms yet increasingly we miss out nowadays. It's interesting to note that, with the exception of last Saturday, this years best occurrences of thunder and lightning have been from Polar Maritime airmasses here.

[Rain123]

Any chance of a rumble today?

[NO LONGER POSTING]

Where did this come from?

 

"goes of to check charts"

 

ssued at: 
1022 on Fri 28 Aug 2015

Valid from: 
0015 on Sun 30 Aug 2015

Valid to: 
2350 on Sun 30 Aug 2015

Heavy showers and possibly some more prolonged rain is expected to affect southeastern parts of England at times during Sunday. Rain could be heavy, with the risk of some torrential downpours whilst lightning may well be an additional hazard at times.

Very localised impacts from standing water or flooding from fast responding water courses may affect travel and some outdoor events and activities. A frontal system, currently developing near the Azores, is expected to push northeast towards the UK later on Saturday, then becoming slow-moving across the southeast on Sunday. Ripples of energy running along the front will give rise to organised showers or more prolonged periods of rain. Furthermore, thunderstorms which are likely to develop across northern France may come north into the warning area, leading to some torrential downpours.

30-50 mm of rain is possible in the warning area, with locally as much as 25 mm falling in a few hours. Added to the heavy rainfall this area has experienced over the last week, some issues from standing water or very localised flooding are possible.

This is a very complex development, and the warning area, as well as warning period, may well be updated as confidence in developments increase.

[Paul1968]

It would make a nice change if any storms that did develop over Northern France actually made it to the SE instead of the North sea or Belgium as so often has been the case this Summer.

[Harry]

 

Where did this come from?

 

"goes of to check charts"

 

ssued at: 

1022 on Fri 28 Aug 2015

Valid from: 

0015 on Sun 30 Aug 2015

Valid to: 

2350 on Sun 30 Aug 2015

Heavy showers and possibly some more prolonged rain is expected to affect southeastern parts of England at times during Sunday. Rain could be heavy, with the risk of some torrential downpours whilst lightning may well be an additional hazard at times.

Very localised impacts from standing water or flooding from fast responding water courses may affect travel and some outdoor events and activities. A frontal system, currently developing near the Azores, is expected to push northeast towards the UK later on Saturday, then becoming slow-moving across the southeast on Sunday. Ripples of energy running along the front will give rise to organised showers or more prolonged periods of rain. Furthermore, thunderstorms which are likely to develop across northern France may come north into the warning area, leading to some torrential downpours.

30-50 mm of rain is possible in the warning area, with locally as much as 25 mm falling in a few hours. Added to the heavy rainfall this area has experienced over the last week, some issues from standing water or very localised flooding are possible.

This is a very complex development, and the warning area, as well as warning period, may well be updated as confidence in developments increase.

 

 

I've been watching this for several days now and it is proper knife-edge stuff. 

 

Having been focussing primarily on GFS, it has been showing a large build up of instability literally the other side of the Channel, but has been largely keen to keep it there. It is all attached to a significant front laying diagonally across N/C Europe - for example, yesterday across France - to the north of the front temperatures were held back at around 15-16C, while south of the front (literally a mile or two the other side) temperatures were 26-28C+. As the HP builds in today and tomorrow, it tries to nudge some of that heat/humidity northwards, however is resisted by a predominately NW flow originating from the large area of LP to our NW - the result is the front currently present.  

 

As the HP establishes, a flabby low is going to run out of Iberia, across the Bay of Biscay and across N France through Sunday, so that by midnight it will sitting somewhere over N France off of the SE-UK coastline. Depending on where this runs will depend on whether that hot and unstable air reaches us.

 

Around half the runs have been keen to throw some storms north across the far SE, while other runs (usually the 18z) very much keen to keep it over France/Benelux. The trend over the past 24-36 hours has been both to delay it and stunt its northerly extent, so that the UK misses out entirely. Today however, the trend has altered slightly - the 12z NMM 5, for example, now indicates up to 2,000 J/Kg running across Kent and Sussex during late Sunday/early Monday.

 

Some runs are keeping everything well and truly over the Channel, while some runs are bringing some juice into play over the SE-UK. We all know the form - it could become a more widespread event, or stay over the continent altogether.

 

But that explains the MetO warning - although I am slightly puzzled about the duration of the warning as the highest storm potential currently resides through Sunday night/Monday AM 

Edited August 28, 2015 by Harry

[Sprites]

MCS kent clipper sunday, depending on how far north the waving warm front gets on Saturday. Could be stratiform rain with the North sea getting the lightning... If you live in Margate keep your unusable 64x zoom handy.

Edited August 28, 2015 by Sprites

[stainesbloke]

MCS kent clipper sunday, depending on how far north the waving warm front gets on Saturday. Could be stratiform rain with the North sea getting the lightning... If you live in Margate keep your unusable 64x zoom handy.

Yup, no doubt all the interesting weather staying over the Channel with us getting the cold rain. Repeat of Wednesday possibly. Might be worth heading to Belgium instead?

[Weather-history]

Cotton wool balls, caulies and mash potatoes

[Speedway Slider]

So, what's the difference between a "Low" & a "Flabby Low"?

[Singularity]

Each and every model run differs with the details, but I've noticed a trend toward Monday seeing a lot of atmospheric moisture being rained out across the south. It could end up being a thoroughly wet day there, but only if the heat and moisture pushes far enough north Sunday evening and overnight.

 

The Sunday threat has been very hit and miss - about as much as I can ever recall seeing at such short range. In fact, there's the potential for a band of precipitation - showery or persistent - to develop across part of the south tomorrow afternoon, but no two model runs agree on this. Even nowcasting may struggle to pin it down.

 

 

Like Harry, I spotted the potential many days ago, as the clash between hot European air and cool Atlantic air looked ripe for downpours, but the lack of a distinct area of low pressure to drive developments led to a lot of forecasts lacking in precipitation across Southern England up until about 48 hours ago. Only since then have areas of enhanced instability started to become apparent. Such is the nature of thermal ('heat') lows, which are largely a result of rising motion. In theory, the thermal low should be capable of developing into a baroclinic low with distinct frontal boundaries as the hot and cool airmasses collide, but the pace and location this is seemingly anyone's guess at this point in time.

[Harry]

Anyone in doubt about how close it will be, take a look at estofex, in particular the unusual extended forecast for Sunday to Monday which shows the far SE clipped by the Lvl 1/50% zone.

There is reference to perhaps broadening the zone.

Certainly one to keep a close eye on

[NO LONGER POSTING]

Interest for tonight to. Not so much for thunderstorms but Euro4 and the net weather model both pick up some very intense lines of rain moving and developing across the south East later this afternoon and over night

[Sparkiee storm]

Hi all, new fresh shiny face to the community    , been reading for a long time and thought it was time to sign up.

 

Anyways looks okay towards the southeast corner for tomorrow night especially, but lightning as we have seen a couple of times this summer may stay over the near continent, but some surprises may be likely, also a chance of some flash flooding again as the met has also saw issuing an early warning.

[legritter]

Hi all, new fresh shiny face to the community    , been reading for a long time and thought it was time to sign up.

 

Anyways looks okay towards the southeast corner for tomorrow night especially, but lightning as we have seen a couple of times this summer may stay over the near continent, but some surprises may be likely, also a chance of some flash flooding again as the met has also saw issuing an early warning.

Nice of you too pop in and post Welcome ,its going to be a radar watchers situation i think with any thundery potential ,even the professionals are scratching their heads ,although now are firming up on any potential ,so today sees the risk of rain and some thunder extending further north than previousely forecast .certainly a very interesting weather pattern on todays fax charts  lets hope it can give some of us the action we are looking for cheers 

[A.J]

Nice of you too pop in and post Welcome ,its going to be a radar watchers situation i think with any thundery potential ,even the professionals are scratching their heads ,although now are firming up on any potential ,so today sees the risk of rain and some thunder extending further north than previousely forecast .certainly a very interesting weather pattern on todays fax charts  lets hope it can give some of us the action we are looking for cheers 

highly unlikely there'll be anything for our neck of the woods to be fair legritter...far south east only (with some pop corn convection for the northern UK)

[Sparkiee storm]

Nice of you too pop in and post Welcome ,its going to be a radar watchers situation i think with any thundery potential ,even the professionals are scratching their heads ,although now are firming up on any potential ,so today sees the risk of rain and some thunder extending further north than previousely forecast .certainly a very interesting weather pattern on todays fax charts  lets hope it can give some of us the action we are looking for cheers 

  and yeah, watched the last few forecasts and seen the confidence has firmed up. I doubt thunder will extend to far north though.

[sunnijim]

Storms crossing the channel now. The front wriggling much further West and North than previously thought.

[Harry]

Well in theory I couldn't be better placed the next couple of days down in warm and humid Dymchurch!

Fingers crossed something blows ashore

[NO LONGER POSTING]

Well in theory I couldn't be better placed the next couple of days down in warm and humid Dymchurch!

Fingers crossed something blows ashore

The further north today's front goes, I would assume better odds on for tomorrow, just out of interest you seen what the EURO4 has churned out for tomorrow and Monday.. Could be some flooding issues... Edited August 29, 2015 by Surrey

[Harry]

The further north today's front goes, I would assume better odds on for tomorrow, just out of interest you seen what the EURO4 has churned out for tomorrow and Monday.. Could be some flooding issues...

Internet access down here is weak at best.

If anyone can post charts would be very grateful

[<<Ryan>>]

Pretty quiet in here this evening? A few storms out in the channel, hopefully they can nudge their way inland! I'm off down to Hastings this evening, so should at least see a couple flashes out to sea

[Harry]

Blitzortung going nuts with the storms in the Channel - going to come fairly close by the looks of it though no definite visuals of any lightning yet, surprising as it's now dark.

[NO LONGER POSTING]

Ahahhahahahaha check the beast out in the Atlantic lmfao..

Not sure I've ever seen something like that before..

Cool

[Harry]

Just heard a lovely deep rolling peel from the channel - though haven't seen a flash yet! Odd