Convective Storm/Discussion thread - 02/09/16 onwards

[Chris.R]

I feel the Met  are massively underplaying temperatures for tomorrow. they did today and GFS  was closer to the mark. It is predicting near 30°C maximums for tomorrow, where as the Met go for more like 25°C. The GFS has been more accurate for me in previous situations like this so let's see what happens. It also shows some very interesting convective potential tomorrow evening, in fact it looks so interesting that I would be getting very excited indeed if the Met was onboard as well with that. 

Edited September 12, 2016 by Chris.R

[Harsh Climate]

I'm suprised that there is little mention of possible storms Tue/Wed yet we have cracking CAPE charts, and the synoptics and temperatures look taylor made for big storms????

 

I often find that in my occasion at least, the best home grown storms come out of the blue albeit well scattered, I wonder if tomorrow/wed will be like this??

 

Edited September 12, 2016 by Harsh Climate

[cheese]

5 minutes ago, Chris.R said:

I feel the Met  are massively underplaying temperatures for tomorrow. they did today an they did today and GFS  was closer to the mark. It is predicting near  30°C maximums  tomorrow ,  where as the Met  go for around 25°C. The GFS  has been more accurate to me in previous situations like this so let's see what happens. It  also  shows some very interesting convective potential tomorrow evening. 

Yes, 24C today despite the cloud, above the BBC's 22C.

Edited September 12, 2016 by cheese

[Chris.R]

9 minutes ago, cheese said:

Yes, 24C today despite the cloud, above the BBC's 22C.

 Yes, same here. Tomorrow in my case I will also have an offshore breeze which should  promote the  highest temperatures around here. I would not be surprised at all to see reports of 30°C around the region, probably near the coast. An interesting few days coming up. 

[Harsh Climate]

1 minute ago, Chris.R said:

 Yes, same here. Tomorrow in my case I will also have an offshore breeze which should  promote the  highest temperatures around here. I would not be surprised at all to see reports of 30°C around the region, probably near the coast. An interesting few days coming up. 

Surely an offshore breeze would negate the temperatures. The highest temperatures are usually where there is little wind.

[Chris.R]

3 minutes ago, Harsh Climate said:

Surely an offshore breeze would negate the temperatures. The highest temperatures are usually where there is little wind.

 Perhaps you would expect that to be the case, but having lived here all my life I can say that an offshore breeze is always good around here. when there is little  Wind, a sea-breeze  Will often develop keeping temperatures suppressed, but a nice fresh  breeze from the land does the  opposite. 

[Harsh Climate]

2 minutes ago, Chris.R said:

 Perhaps you would expect that to be the case, but having lived here all my life I can say that an offshore breeze is always good around here. when there is little  Wind, a sea-breeze  Will often develop keeping temperatures suppressed, but a nice fresh  breeze from the land does the  opposite. 

My bad I got offshore breeze mistaken with sea breeze lol. You are correct.

[Thunderstruck]

So the main risk area misses us again. For the part of the UK getting the highest temperature, you'd expect a lot more based on the heat at times over summer. But since there seems to be low confidence ahead of this next event, let's not rule ourselves out

[Flash bang flash bang etc]

Planning to be out and about tomorrow night but I think the central south down to the south east corner should be reserved the best of the convection to reset the balance!

 

what are the thoughts on weds evening's potential?

[Chris.R]

20 minutes ago, Harsh Climate said:

My bad I got offshore breeze mistaken with sea breeze lol. You are correct.

Easily done. I used to do that all the time. 

If temperatures end up  higher than expected, let's see if the cap can be broken as there are some really tasty storm parameters around for tomorrow evening. 

Edited September 12, 2016 by Chris.R

[Mapantz]

2 minutes ago, Jcweather said:

So the main risk area misses us again. For the part of the UK getting the highest temperature, you'd expect a lot more based on the heat at times over summer. But since there seems to be low confidence ahead of this next event, let's not rule ourselves out

It's no good without a trigger of some sort. Strong capping has been quite substantial in the plumes this year. Although, that last thundery episode did deliver a lot of lightning across many areas.

[East_England_Stormchaser91]

I think they could crop up pretty much anywhere tomorrow. Any local convergence that develops could create a storm just about anywhere from NW England across to Yorkshire and anywhere south of that. The potential is there right across any of the parts mentioned. Imports into S England and into east Anglia too from the Low Countries and France cannot be ruled out either. 

[Harsh Climate]

Mapants, hopefully this small developing low willa ct as a trigger as well as the very high temperatures. My only concerns are there are no troughs or fronts anywhere in sight tue/wed and its dark by 7:30pm. If nothing good has developed by 6:30pm either day nothing significant will develope

I would expect at least a few isolated storms/thundery showers to develope though. Favoured area has to be north west england!

[carl1980]

Estofex looks good level 1 around here level 2 around south Wales and south West England 

[Andy Bown]

1 hour ago, Harsh Climate said:

Mapants, hopefully this small developing low willa ct as a trigger as well as the very high temperatures. My only concerns are there are no troughs or fronts anywhere in sight tue/wed and its dark by 7:30pm. If nothing good has developed by 6:30pm either day nothing significant will develope

Not strictly true. 18th September 2014 had an intense thundery plume that destabilised near midnight producing fantastic electrical storms from the South coast and moving North a long way inland.

[Mapantz]

Courtesy of: http://www.convectiveweather.co.uk/

Quote

Day 2 Convective Outlook

VALID 06:00 UTC Tue 13 Sep 2016 - 05:59 UTC Wed 14 Sep 2016

ISSUED 20:31 UTC Mon 12 Sep 2016

ISSUED BY: Dan

As the sharp Atlantic upper trough disrupts over Biscay during Tuesday, backed mean flow will continue to advect a very warm, moist airmass northwards across the British Isles. The passage of various shortwaves running northwards in this flow may serve as the forcing mechanism to destabilise the mid-levels, east of the main frontal boundary, with scope for outbreaks of primarily elevated convection likely at times - beginning across SW Eng / S Wales on Tuesday morning, with this zone shifting north through the day. This may be accompanied by further medium-level destabilisation farther east towards Dorset etc, but some uncertainty as to how far east elevated convection may occur.

There is also some reasonable agreement for another round of elevated thunderstorm activity over the Channel Islands / English Channel on Tuesday night, advecting into Cornwall and perhaps Devon.

 

Notably steep mid-level lapse rates and MLCAPE 800-1,200 Jkg-1 suggests any storms that do develop on Tuesday, especially farther east, will produce quite frequent lightning. 

 

However, given rather weak forcing, the biggest uncertainty is coverage, and this is the primary reason for refraining from issuing any higher threat levels - it is quite likely that some or many areas within the SLGT could remain void of lightning. It is difficult to portray the balance between the likelihood of a shower producing lightning (which is high-very high) vs the likelihood of a shower occurring in any one location (low-moderate). 

 

If any convection can become rooted within the boundary layer, then heavy rain and large hail up to 3.0-4.0cm in diameter would be possible - a SVR has been issued to highlight the area at risk of this. There are some suggestions for the potential (at least) of surface-based convection during the evening hours over N Wales / NW England, particularly where elements of orographic forcing from upslope flow over the Pennines may a play a role etc. Forecast soundings suggest a fairly substantial warm nose (750-900mb) will need to be eroded to achieve this.

 

Given the large amount of uncertainty, this forecast may be updated as confidence improves - and it is possible that the SLGT may need extending into parts of S Scotland, for example.

 

Edited September 12, 2016 by Mapantz

[weirpig]

I didn't expect that from esofex mind you haven't been looking at the models recently  just in the level 1 warning zone  looks fun and games for the south west 

[Harry]

Going to be another frustrating couple of days for me I think...heat and humidity but no real potential...it literally dancing around my location.

That is not to say I bemoan at all the exciting 48 hours or so out west...reparations for what must feel like a disappointing few years.

Interesting that there are differences between Dan on CWUK and Estofex in terms of the focal point for severe weather tomorrow, the latter favouring more SW parts whereas Dan further NW.

 

[Chris K]

Certainly look interesting above, yet this evenings local BBC forecast mentions that most places in the SW are likely to stay dry tomorrow...in fact BBC charts in general keep any rainfall just off the W coasts.

UKMO fax chart for tomorrow has some interest, as I would expect showers/thunderstorms to develop on this feature over the W country and parts of S England, perhaps initiating as it pushes North. Seems to match up with the zones forecast in the above posts then.

I am feeling the usual pessimistic self, but will keep an eye on things tomorrow.

[East_England_Stormchaser91]

All eyes on the track of that low and associated fronts begin from now really. Going to be a very interesting 48 hours to come! 

[SteveB]

6 minutes ago, Chris K said:

Certainly look interesting above, yet this evenings local BBC forecast mentions that most places in the SW are likely to stay dry tomorrow...in fact BBC charts in general keep any rainfall just off the W coasts.

UKMO fax chart for tomorrow has some interest, as I would expect showers/thunderstorms to develop on this feature over the W country and parts of S England, perhaps initiating as it pushes North. Seems to match up with the zones forecast in the above posts then.

I am feeling the usual pessimistic self, but will keep an eye on things tomorrow.

BBC having non of it for our area.

[Chris K]

7 minutes ago, SteveB said:

BBC having non of it for our area.

Indeed, hence my pessimism. But as always, we await to see what happens on radars/satellite! 

[SteveB]

9 minutes ago, Chris K said:

Indeed, hence my pessimism. But as always, we await to see what happens on radars/satellite! 

After the complete and utter bust of this Spring and summer storm season, it would be ironic to get one in Autumn.

As ever- ain't holding my breath

[Singularity]

That ESTOFEX outlook talks of the boundary moving east across Spain and France which is in line with the models, but it also applies that to Southwest England which seems contrary to the model consensus that places low pressure S of the UK with the boundary quasi-stationary or even drifting a little west. This results in more sporadic and localised instability wherever an overlap of upper and lower dynamics manages to occur. Who knows - that could produce an isolated severe storm or storm cluster such has happened on 27th August. That beast grew from a Channel import while moving over Dorset, feeding on surface heating ahead of it to grow increasingly large as it progressed to the NE. Unfortunately all I got from that system was a lot of outflow which prevented a hot sunny day while not delivering any lightning or even thunder to compensate. A day I wish I'd forgotten already!

Heres hoping I can score either the heat or the storms tomorrow and not neither - but being in the perispheral zone again does not fill me with hope!

[Supacell]

There is still enough disagreement between the models for me to await what is showing in the morning before I decide if I will chase and then if I do, where I will go.