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Storms and Convective Discussion - 20th April 2019 onwards

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 When looking at the convective prospects for tomorrow and into Wednesday we may need to think about two separate thunderstorm potential conditions, neither of which is fully nailed down by the models yet. Broadly speaking we have a low pressure system to the west of Portugal which has quite a sharp vorticity maximum associated with it. This is causing warm air to be moved northwards and up over the Iberian peninsular  (North Spain). The key thing to watch is how much convection takes place over Northern Spain today  (just starting to occur) as this will give some indications as to which modeled solutions are correct. It is always worth remembering that typically modelling moves things eastwards a day before any potential and then slightly westwards on the day. However the vorticity embedded in the low of Portugal is more than Forecast so all of the modelling might be a bit off (Looks like it could give some pretty windy conditions as well if it does not slacken off as forecast).
 The modelling suggests tomorrow the warm air destabilizes as cooler air from the trough start to over run it. This should occur out over the Bay of Biscay and then significantly over France. In effect a surface low develops ahead of the storm out towards Portugal as thunderstorms build over France. For the UK the suggestion is that destabilization occurs in the Bay of Biscay around Midday with convection build as this area comes on shore. Instability might be weak during this period but wind shear profiles look fairly potent. Later on during the night we have elevated storms (Not surface based) moving into the south east corner of the UK. Instability is likely to be high and tops should reach a decent height so we could be in for quite a lightning show. Elevated storms do not always produce lots of rain but in this case the moisture profile suggests some significant down pours.

 The trouble is that at the moment I am not convinced by any of the modelling. The storm to the west of Portugal looks more potent than thought, time for the warm air to rise over North Spain is relatively short and discrepancies in model output mean any forecast is relatively worthless in my view at this point.

myov3uAIKJYJ9.jpg

nmmuk3hrpreciptue12.png

nmmukwindtue12.png

nmmuk3hrpreciptue15.png

nmmuk3hrpreciptue18.png

nmmuk3hrprecipwed03.png

sound-London-36.png

sound-London-48.png

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6 minutes ago, BrickFielder said:

 When looking at the convective prospects for tomorrow and into Wednesday we may need to think about two separate thunderstorm potential conditions, neither of which is fully nailed down by the models yet. Broadly speaking we have a low pressure system to the west of Portugal which has quite a sharp vorticity maximum associated with it. This is causing warm air to be moved northwards and up over the Iberian peninsular  (North Spain). The key thing to watch is how much convection takes place over Northern Spain today  (just starting to occur) as this will give some indications as to which modeled solutions are correct. It is always worth remembering that typically modelling moves things eastwards a day before any potential and then slightly westwards on the day. However the vorticity embedded in the low of Portugal is more than Forecast so all of the modelling might be a bit off (Looks like it could give some pretty windy conditions as well if it does not slacken off as forecast).
 The modelling suggests tomorrow the warm air destabilizes as cooler air from the trough start to over run it. This should occur out over the Bay of Biscay and then significantly over France. In effect a surface low develops ahead of the storm out towards Portugal as thunderstorms build over France. For the UK the suggestion is that destabilization occurs in the Bay of Biscay around Midday with convection build as this area comes on shore. Instability might be weak during this period but wind shear profiles look fairly potent. Later on during the night we have elevated storms (Not surface based) moving into the south east corner of the UK. Instability is likely to be high and tops should reach a decent height so we could be in for quite a lightning show. Elevated storms do not always produce lots of rain but in this case the moisture profile suggests some significant down pours.

 The trouble is that at the moment I am not convinced by any of the modelling. The storm to the west of Portugal looks more potent than thought, time for the warm air to rise over North Spain is relatively short and discrepancies in model output mean any forecast is relatively worthless in my view at this point.

myov3uAIKJYJ9.jpg

nmmuk3hrpreciptue12.png

nmmukwindtue12.png

nmmuk3hrpreciptue15.png

nmmuk3hrpreciptue18.png

nmmuk3hrprecipwed03.png

sound-London-36.png

sound-London-48.png

Wow your chart shows that first big white/red blob go pretty over the top of me before going east. Has the main risk been shifted west? 

Don't get my hopes up lol. 

Edited by Swansonson69

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While most models are showing that the overnight storms are going to be in the south-east, the Met Office thinks that the thunderstorms will develop over the English Channel and move their way north-east.

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15 minutes ago, zmstorm said:

While most models are showing that the overnight storms are going to be in the south-east, the Met Office thinks that the thunderstorms will develop over the English Channel and move their way north-east.

They must see something that everything else is missing. I wonder if it'll be a case of the rest of the models following suit. 

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As with any convective potential,nowcast and radar watching is the key here guys,the models just give a general area,we have seen this many times (especially with showers) 

but at least it should be busy in here come tomorrow?

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11 minutes ago, Swansonson69 said:

They must see something that everything else is missing. I wonder if it'll be a case of the rest of the models following suit. 

Yeah, and I hope the Met Office are right because if they are then more western areas could have the chance of seeing a decent light display.

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Some good thunderstorms in northern Scotland.

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1 hour ago, Swansonson69 said:

For Kent and the South East. Hope they get some decent storms. 

I kind of meant the naming of the storm.... not the claggy mess approaching us?

We very rarely get get anything from these kind of set-ups in the West Midlands

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1 minute ago, Arnie Pie said:

I kind of meant the naming of the storm.... not the claggy mess approaching us?

We very rarely get get anything from these kind of set-ups in the West Midlands

Ah ok, im in east Midlands. 

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I’m praying that this happens...

D36D182C-677E-4EC3-A39E-2C8C6D829008.pngwindy.com

Edited by Oliver Wyndham-lewis

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This shows rain moving North East with Thunderstorms along the South, maybe this is what the Met Office are looking at?

image.thumb.png.cda1157401628e2358d0ba42f7df6381.png

image.thumb.png.c9b585c7ee19fe2a2bda0872e2f5d874.png

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Not getting excited yet, but the car is camera ready now.

Been very muggy/hot today down here. 

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Yet again, I have to be real, I do think it will be a very lucky shot if we do see activity as far west as the IOW - Peterborough/Lincolnshire line. 

Judging by the steering winds aloft, yet again, I fear that there’s too much westerly component to them. A Kent clipper scenario is what I think will more realistically unfold. I hope I’m wrong however. 

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1 minute ago, Lu. said:

Not getting excited yet, but the car is camera ready now.

Been very muggy/hot today down here. 

Been muggy and hot here aswell in east Midlands. 

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Wouldn’t describe it as hot here but it’s noticeably more humid here now than it was. 

1 hour ago, Purplepixii said:

keeping fingers crossed for Hampshire coast tomorrow ?

? 

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Just now, matt111 said:

Wouldn’t describe it as hot here but it’s noticeably more humid here now than it was. 

? 

Yeah, there have been periods of real heat but more than anything I noticed the cloying air, like it's not "fresh". Ah well, I'll be down the beach tomorrow night if this comes off ⚡

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3 hours ago, Surrey said:

Harry.. You of all people I would have thought know not to fall into the model trap when it comes to predicting thunderstorms.. Bit like snow 

 

Let's get something on radar first lol 

Fair point @Surrey. In my defence I am only relaying what I’m seeing on the models and did highlight that 06z is the most pessimistic of the models. For me the MetO warnings are much wider (for “thunderstorms”) than either GFS or WRF-NMM have been indicating for quite some time now. Meaningful instability never really moves out of SE/EA (although I obviously hope it is more extensive than currently showing) and on the 06z it is limited just to Kent and Sussex. 

Experience has taught me that if the GFS and WRF-NMM aren’t showing the juice, then don’t expect fireworks even if it rains hard...12z GFS shows a clear area of heavy rain moving across SE quarter tomorrow evening/night but then offers us limited or no instability (neither surface based nor elevated). Therefore heavy rain with an isolated flash is what this suggests to me.

I have my fingers firmly crossed for a westward trend and am encouraged by Brickfielder’s observations above re westward trends in the final 24 hours. And agreed; I shouldn’t model gaze for too long!

 

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Keeping an eye on this. With a history of every storm avoiding me, I'm hoping to see some action Tuesday evening/Wednesday.  Also waiting to see Estofex's take on things. This late afternoon seems to have acquired a cooler touch as cool air has lapped northwards from the Channel.

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41 minutes ago, Harry said:

Fair point @Surrey. In my defence I am only relaying what I’m seeing on the models and did highlight that 06z is the most pessimistic of the models. For me the MetO warnings are much wider (for “thunderstorms”) than either GFS or WRF-NMM have been indicating for quite some time now. Meaningful instability never really moves out of SE/EA (although I obviously hope it is more extensive than currently showing) and on the 06z it is limited just to Kent and Sussex. 

Experience has taught me that if the GFS and WRF-NMM aren’t showing the juice, then don’t expect fireworks even if it rains hard...12z GFS shows a clear area of heavy rain moving across SE quarter tomorrow evening/night but then offers us limited or no instability (neither surface based nor elevated). Therefore heavy rain with an isolated flash is what this suggests to me.

I have my fingers firmly crossed for a westward trend and am encouraged by Brickfielder’s observations above re westward trends in the final 24 hours. And agreed; I shouldn’t model gaze for too long!

 

If they get elevation then hopefully they won't rely to much on Cape 

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8 minutes ago, Surrey said:

If they get elevation then hopefully they won't rely to much on Cape 

Would even elevated storms not be reliant on MUCAPE?

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8 minutes ago, Surrey said:

If they get elevation then hopefully they won't rely to much on Cape 

So surface based relies more on CAPE and elevated doesn't rely on much CAPE?  

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3 minutes ago, Swansonson69 said:

So surface based relies more on CAPE and elevated doesn't rely on much CAPE?  

Elevated stuff gets its fuel from Mid level/Mixed layer CAPE and high theta W values (the plume) which destabilises typically from the west as barometric pressure drops. Surface based activity relies on SB CAPE. If conditions are right though, elevated activity during the day can sometimes transition into a surface based storm, and vice versa when daytime heating wanes. 

Edited by East_England_Stormchaser91
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10 minutes ago, East_England_Stormchaser91 said:

Elevated stuff gets its fuel from Mid level/Mixed layer CAPE and high theta W values (the plume) which destabilises typically from the west as barometric pressure drops. Surface based activity relies on SB CAPE. If conditions are right though, elevated activity during the day can sometimes transition into a surface based storm, and vice versa when daytime heating wanes. 

Thank you for the information. ?

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