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Supacell

Convective/Storm Discussion Thread - 19th May 2018 onwards

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22 minutes ago, Supacell said:

I have to admit to be a little excited about the prospects this coming weekend with several rounds of thunderstorms. A risk some could get as far north as here on Sunday night into Monday but I will be out and about this weekend I expect so will go to them if they don't come to me.

A repeat of 27th May last year would be fantastic. I chose not to chase and wait for storms to come here on that occasion, and went on to regret that decision.

What is your plan are you chasing if so where to? Just curious as I always enjoy your output!

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12 minutes ago, tomjwlx said:

What is your plan are you chasing if so where to? Just curious as I always enjoy your output!

I will be chasing :). There may be storms around during the day tomorrow, but to chase I would need to get more confidence of these in the morning outputs as I am concerned how left over clag from overnight/early morning showers could affect this. In truth though, I think there is a likelihood of some heavy showers and thunderstorms developing across CS England and into the SW and S Wales tomorrow. I will probably aim to be somewhere around the mid M4 corridor which puts me in a good position for both day time possibilities and then to intercept anything that moves across from the south in the evening. 

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1 hour ago, Supacell said:

I will be chasing :). There may be storms around during the day tomorrow, but to chase I would need to get more confidence of these in the morning outputs as I am concerned how left over clag from overnight/early morning showers could affect this. In truth though, I think there is a likelihood of some heavy showers and thunderstorms developing across CS England and into the SW and S Wales tomorrow. I will probably aim to be somewhere around the mid M4 corridor which puts me in a good position for both day time possibilities and then to intercept anything that moves across from the south in the evening. 

I’ll probably be in a similar area. Was considering the M3 to be a good route. Don’t know where to start but as the storms may track that way up towards west London, a good spot to end up *might* be up on Richmond hill later on

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Day 2 Convective Outlook

VALID 06:00 UTC Sat 26 May 2018 - 05:59 UTC Sun 27 May 2018

ISSUED 22:40 UTC Fri 25 May 2018

ISSUED BY: Dan

Plume events are often fraught with uncertainty, primarily due to poor NWP modelling of deep convection generated by mid-level instability. In these types of situations, including today, it is best to take a broad-brush approach and try to highlight trends, rather than specifics - basically, expect the unexpected! The latest model guidance is much further north and a lot quicker with developments than data had been suggesting just 12 hours ago. It is likely some areas within the SLGT could remain lightning free, and the forecast may need to be altered if confidence improves - it rarely goes to plan...

 
There are reasonable signs for an area of elevated convection to be drifting across S / SE England at the beginning of this forecast period, continuing to move NW-wards through Saturday morning. Questionable as to how much lightning there will be with this activity given weakening instability, though forecast profiles do suggest some reasonable shear to help with some organisation. Either way, whatever activity there is will likely weaken with time as it continues to migrate across the Midlands and into Wales.
A secondary pulse of elevated convection may develop and move NW-wards across SW England late morning into the afternoon, which would have a better chance of producing lightning - but this is a weaker signal amongst model guidance.
 
This then leaves a window of opportunity during the afternoon for surface-based thunderstorms to occur. However, the atmosphere will be largely capped by a warm nose at 850-900mb, and so despite increasing instability it is possible very little will actually develop. Greatest potential perhaps across Dorset, Somerset and Gloucestershire, but this very much dependent on enough surface heating to break the cap, which is uncertain due to the potential for extensive mid/upper level cloud associated with earlier elevated convection. Should an isolated thunderstorm develop, it may be severe, capable of producing hail up to 2.0cm in diameter and localised surface water flooding.
 
The potential for thunderstorms then increases during Saturday evening and night, with numerous elevated thunderstorms likely to develop over the English Channel containing frequent lightning and perhaps some hail. The vast majority of model guidance would suggest thunderstorms will move to the NW, putting SW England and the West Country at greatest risk, broadly Isle of Wight westwards. However, ECMWF has been very consistent over several runs (now joined by 12z EURO4) to produce a much more bifurcated flow, which would then take a very active cluster of thunderstorms NE-wards over Hampshire, Sussex and towards the London area by the early hours of Sunday.
Given the large spread of possible areas affected, it is difficult to pin down a MDT area with any significant confidence - though worth stressing the ECMWF (and EURO4) tends to have a good handle of elevated convection, and its consistent signal over multiple runs is somewhat reassuring. As a result, have followed these trends for the MDT - though if other models are correct, this may need shifting westwards to cover more of Devon and Cornwall.
 

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I just out my dads living room window it is cloudy out side so that going stop things from later like thunderStroms   to developed over here in Salisbury in Wiltshire

Edited by Tom dewey likes thunder

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 Upgrade on WRF 18 Z for my location. All the ingredients are there for some good surface based and elivated storms on Sunday, daytime and the following night respectively. Just need to see if a trigger can be utilised. 

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9 minutes ago, Flash bang flash bang etc said:

The game is well and truly on!

We have sun!!!

Now watch those temperatures rocket...

💣💣💣

I see that clear gap moving into southern England, wasn't expecting that. If I'm honest I would like to a nice sunny day with long hours of sunshine then storms around 6-7pm into the evening which the euro4 does suggest, it then goes absolutely insane for south east England Sunday night... Think I might have been a bit reserved yesterday.. 

Note most senior forcasters are throwing the high RES models out and waiting to see on developments 

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ay 1 Convective Outlook

VALID 06:00 UTC Sat 26 May 2018 - 05:59 UTC Sun 27 May 2018

ISSUED 06:49 UTC Sat 26 May 2018

ISSUED BY: Dan

 

UPDATE 06:49 UTC All areas extended north to cater for quicker arrival in latest model guidance. MDT expanded westwards to include Devon and Cornwall. Note: bifurcating flow tends to leave a gap between two main clusters of thunderstorms, so it is possible not everywhere in the MDT will be affected by lightning - but hard to specify exactly which areas might remain lightning-free
 

Plume events are often fraught with uncertainty, primarily due to poor NWP modelling of deep convection generated by mid-level instability. In these types of situations, including today, it is best to take a broad-brush approach and try to highlight trends, rather than specifics - basically, expect the unexpected! The latest model guidance is much further north and a lot quicker with developments than data had been suggesting just 12 hours ago. It is likely some areas within the SLGT could remain lightning free, and the forecast may need to be altered if confidence improves - it rarely goes to plan...

 
There are reasonable signs for an area of elevated convection to be drifting across S / SE England at the beginning of this forecast period, continuing to move NW-wards through Saturday morning. Questionable as to how much lightning there will be with this activity given weakening instability, though forecast profiles do suggest some reasonable shear to help with some organisation. Either way, whatever activity there is will likely weaken with time as it continues to migrate across the Midlands and into Wales.
A secondary pulse of elevated convection may develop and move NW-wards across SW England late morning into the afternoon, which would have a better chance of producing lightning - but this is a weaker signal amongst model guidance.
 
This then leaves a window of opportunity during the afternoon for surface-based thunderstorms to occur. However, the atmosphere will be largely capped by a warm nose at 850-900mb, and so despite increasing instability it is possible very little will actually develop. Greatest potential perhaps across Dorset, Somerset and Gloucestershire, but this very much dependent on enough surface heating to break the cap, which is uncertain due to the potential for extensive mid/upper level cloud associated with earlier elevated convection. Should an isolated thunderstorm develop, it may be severe, capable of producing hail up to 2.0cm in diameter and localised surface water flooding.
 
The potential for thunderstorms then increases during Saturday evening and night, with numerous elevated thunderstorms likely to develop over the English Channel containing frequent lightning and perhaps some hail. The vast majority of model guidance would suggest thunderstorms will move to the NW, putting SW England and the West Country at greatest risk, broadly Isle of Wight westwards. However, ECMWF has been very consistent over several runs (now joined by 12z EURO4) to produce a much more bifurcated flow, which would then take a very active cluster of thunderstorms NE-wards over Hampshire, Sussex and towards the London area by the early hours of Sunday.
Given the large spread of possible areas affected, it is difficult to pin down a MDT area with any significant confidence - though worth stressing the ECMWF (and EURO4) tends to have a good handle of elevated convection, and its consistent signal over multiple runs is somewhat reassuring. As a result, have followed these trends for the MDT - though if other models are correct, this may need shifting westwards to cover more of Devon and Cornwall.
 

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16 minutes ago, Tom dewey likes thunder said:

I can't this cloud clearing up yet over this area of Wiltshire and is it Sunny in Dorset ?

It's still very overcast here in Southampton too but don't worry, the main storm action isn't expected until much later into this evening and tonight and it looks like skies are clearing from the south east.  Impossible to pin down specific areas yet but looks like most of southern England is in the game at least.

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19 minutes ago, Tom dewey likes thunder said:

I can't this cloud clearing up yet over this area of Wiltshire and is it Sunny in Dorset ?

Tom I suggest looking at the Sat24, which is a satellite image animation and you can use it to kind of predict when the cloud will clear.

Use this link: https://en.sat24.com/HD/en/gb/visual

I expect for our region the cloud will disperse by midday.

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That’s good that skies are clearing from the South East. Even watching a very boring TV show would be more entertaining than looking at this convection-suppressing white thing in the sky. ☁️🔫

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I see on Lightning maps there were a couple of strikes near Colchester already!

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Big cloud clearance on the SE coast as I left for work at 6am.

Clear skies drifting in from the SE and a humid sun

Soon drove into the murky, drizzly and misty weather as I headed for SE London though.Hoping the clear skies arrive soon.

Edited by sunnijim

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Yes satellite shows the skies clearing in the SE. 

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Met office still not fancying SE for storms this weekend. Everywhere else seems to though so we'll see, 

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10 minutes ago, Lauren said:

Met office still not fancying SE for storms this weekend. Everywhere else seems to though so we'll see, 

I was beginning to become a little dispondent, until I saw the Euro4 model for tomorrow evening (prompted by Dan’s forecast on CW). There’s a lot of instability available so we just need a trigger to come along...whether that’s the occluded front tonight stretching a bit further east, a cheeky trough appearing or a CZ. 

I can’t count the times storms have been expected further west, only for them to erupt further east too. 

In the meantime I’m just looking forward to this grey murk to do one 😁

 

Edited by Harry

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How best do I read the Euro 4?

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There will be the possibility of a number of rounds of heavy showers and possible thunderstorms today and this week with different locations being in the firing line from day to day. This should mean a number of us see at least something. I will concentrate on today and tonight.

There are elevated showers around southern England through this morning, but this holds a low risk of lightning. It is showing up as messy convective rainfall and lightning detectors are already picking up the odd sferic around Essex. There is a lot of cloud around but it is humid with dewpoints around the low teens. The risk of further showery rain and the odd flash/rumble continues through the morning.

There is then the risk of surface based thunderstorms developing during the afternoon should the sun break through, which is quite likely it will (already brightening up across the far SE). These are by no means guaranteed and some models are not keen. The NMM high resolution model develops a single storm somewhere around the Bristol channel and takes it in a northwesterly direction into South Wales. Don't take this distribution literally, although I would expect the West Country and Wales are most at risk from these.

1189673541_shower4pm.thumb.png.e747c837493e91a0ec73fb49c8a5460e.png

Any storms this afternoon will be developing in an environment of high CAPE, low shear and high moisture (PWAT values over 30mm). Therefore they will be of the pulse type single cell variety but could produce a lot of rainfall in a short space of time along with frequent lightning, gusty winds and quite large hail (~2cm). 

992947946_cape3pm.thumb.png.c229ae7cd5d5b83faa2a6ddbaa077a70.png   169170009_PWAT3pm.thumb.png.9690cc08d94353d92fd05d2298e60804.png

The main event in my opinion arrives this evening across the Channel in the form of some intense elevated thunderstorms as the plume destabilises. Important here is that as these will be elevated and so will not be affected by the cool Channel sea or cloud amounts. They will not affect everyone, as is always the case, but where they do occur they will again have the risk of producing a lot of lightning, large hail, gusty winds and torrential rainfall leading to impacts. The NMM model below gives a guideline but to be honest it is better to use real time observations to gauge where storms will be as no model can boast 100% accuracy.

10pm.thumb.png.2c5e358b65d9a8efc83f222bf52d29d7.png1am.thumb.png.60d5378567c879359386be5896281cac.png

I am most interested in the lightning which I would expect to be frequent at times, maybe very frequent with MUCAPE over 2000j/kg on the NMM model. Again, don't take the spread literally and bear in mind this chart is for midnight and then 6am when the highest CAPE has moved north of the south and south-west.

951333405_cape00am.thumb.png.d5b2dbfb29a38a2fb42e1c20ba3cb4f3.png 373548458_cape6am.thumb.png.523de404a9af967d4973a530d1c76df1.png

Dan (convective weather) has explained that there may be a couple of thunderstorm clusters with a gap in the middle and how it is hard to know where these clusters will form. However, some of us should definitely see some good action later today/tonight and I am happy with this as I will be out there chasing (probably pitching somewhere on the M4).

After this we have tomorrow, where more severe thunderstorms are forecast and these affecting a little further north too. There are then many more opportunities through the rest of the week including the possibility of a storm even arriving on my doorstep (late Sunday). The end of May looks to go out with a bang! 

Edited by Supacell

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