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Storms and Convective Discussion - 20th April 2019 onwards

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Posted (edited)
10 minutes ago, Ben Sainsbury said:

Latest NMM looks interesting? Two areas of interest...

Hmm.thumb.png.10a85e513237f00711650d610416cec6.png

I noticed this earlier today with the ICON and AROME models both going for 2 areas of rainfall with some interest for more western areas tomorrow morning during rush hour. However the latest AROME has since dropped the idea.

ICON 12z still goes for it around 7am for the W country but whether this modelled rainfall is active in terms of lightning is up for debate.

Edited by Chris K

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 Shrewsbury sell has now died electrically. 

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Posted (edited)
4 minutes ago, Chris K said:

I noticed this earlier today with the ICON and AROME models both going for 2 areas of rainfall, but the latest AROME has since dropped the idea.

If this happens, I think it lines up with some forecasts that the strong storms would be to the east, and an area of more generic heavy, maybe thundery rain to the west.

It's not looking as promising for here in the West Midlands. However, for my old home town of Lowestoft, it's looking a bit more potentially exciting. Shame I'm working in the morning or the folks back home would be getting a surprise visit tonight!

Edited by Gord

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1 minute ago, Chris.R said:

 Shrewsbury sell has now died electrically. 

oooh wouldn't say it's died, just taking a breath after all the hard work it has just done

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Just now, Gord said:

If this happens, I think it lines up with some forecasts that the strong storms would be to the east, and an area of more generic heavy, maybe thundery rain to the west.

It's not looking as promising for the West Midlands. For my old home town of Lowestoft, it's looking a bit more potentially exciting. Shame I'm working in the morning or the folks back home would be getting a surprise visit tonight!

That's what the Met Office are going for here with a heavy rain risk in the early hours and through the main part of Tuesday morning. Despite the word 'thundery' used in the text, I doubt we'll get anything electrical here with the main risk much further SE.

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1 minute ago, ancientsolar said:

oooh wouldn't say it's died, just taking a breath after all the hard work it has just done

The parameters at play seem to favour more popcorn storms to the west.

Saying that it’s fine popcorn!

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Posted (edited)

AROME 9z ensembles shows risk of heavy precipitation >20mm over a range of SE England, here overnight to T27:

image.thumb.jpg.dd5bea8dbe94c696e78b14b5c6142f79.jpg

I think  this better  shows the risk than an operational run.  Here tableaux for cumulative precipitation close to Oxford:

table_wlz2.png

And MUCAPE:

table_jct7.png

Edited by Mike Poole

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Posted (edited)
6 minutes ago, ancientsolar said:

oooh wouldn't say it's died, just taking a breath after all the hard work it

Absolute perfect demonstration of the Shrewsbury storm shield in action. They get 10 miles from here, then at least 8/10 times either die or veer off to Birmingham/Staffs/Wales/anywhere else. Never used to, just since 2007.

Edited by Summer of 95

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1 minute ago, Flash bang flash bang etc said:

The parameters at play seem to favour more popcorn storms to the west.

Saying that it’s fine popcorn!

 Wouldn’t surprise me if it’s the on-shore wind. Acts as a natural storm shield. Whenever a cell  gets to a certain latitude it kills it off. 

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Few blue ish skies pocking out through the clouds here now

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Well I’m not staying up until rush hour as I’ll be up by then anyway 😂

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Posted (edited)

Latest icon 15z  seems to push the main band further west  a large area of England under heavy precipitation  

Edited by weirpig

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That one is done, maybe another chance tonight for one of the 2/10. Could see the rain from those cells falling either side of me, one 10-15 miles N, one the same distance S. 

Never heard any rumbles at all

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In addition to Nick F’s forecast, PJB (UKWW) has updated his thoughts for this evening:

 

Update 18:00 BST 

No Changes to earlier Risk Zones but increased to 90% Risk and added a zone of most impact. 


Detail 

Afternoon Temperatures over France in the Paris region have reached around 30-31C, The air lifted here too dry and subsided to produce significant convection. The trajectories at 950mbs / 925mbs take this very warm air westwards towards an area of 925mb confluence to an area to the South of the Cherbourg Peninsula. This area of enhanced confluence just aloft will be enough to initiate convection in a few hours time. At the present aloft there is an area of decreasing positive earth vorticity advection moving NNE from a SSW direction across extreme Northern France and England and Wales. This largely responsible for the decreasing mid level ascent and the clouds thinning and breaking. To the South over Biscay an area of increasing Positive earth vorticity advection is located between 47.5N and 42N and is responsible for the increase in convection over the Bay of Biscay. There is also an area of shear vorticity in the flow and over N Spain a shear axis. During the day the plume of high theta -w has advected northwards across France and the storms will fire in the zone of greatest 850mb moisture and heat for the air rising within the confluence zone to the South of Cherbourg. So we have Southerly flow at 850mbs, easterly flow at 925mbs meeting Northerly flow at 950mbs, and a cooling and increasing spinning environment aloft above 700mbs. This combination of low level confluence, 850mb moisture and cooling and increasingly active kinematic environment aloft will allow for storms to grow rapidly once they form. The 12Z Models are in good agreement in taking the multi-cells to the NE over English Channel - routed to nr 900-920mbs with the perfect 850mb airflow to sustain inflow and to grow daughter cells on the south and south east of the growing organised storm complex. As the storms grow the divergence aloft from the right entrance to a SW Jet stream aloft over Biscay and the increasing positive earth vorticity will allow for outflow to be taken North east wards away from the storms and into another small scale jet over the Central North Sea. Therefore the atmospheric chimney is effectively setting up very nicely for some very active cells indeed to move NE. Supercells are possible as the system grows and there is the added low level confluence to add to further storms which develop over and up the M11 towards the Wash during the latter part of the night, due to some further increase in the low level confluence and a greater amount of upper level divergence and a slight increase in the upper level kinematics over this region during the 03Z to 06Z on Tuesday. Area should be considered to have increase low level helicity and possible super cellular tornado possibilities. (PROB 20-25%) 

Very high rainfall rates of 80/150mm/h are likely as the zone moves North . The French AROME Model somewhat further east with its precipitation field. However there is good agreement from the Dutch Hirlam, ICON, ARPEGE and UKMET 2KM in the zone from Sussex and East Hants, up across Surrey and across Central London and then up the M11 towards Cambridge and the Wash. Frequent Lightning, Flooding and Hail are possible. The small but not negligible risk of Tornado activity later in the period is mentioned above 

Disruption and delays to the Travel Network are extremely likely as well as the power network.  

OVERALL RISK ASSESSMENT IS NOW RAISED TO 90% for the areas mentioned above and in the graphic.

Attached thumbnail(s)

F54928A9-29C8-4DE6-BB4B-7EEF64D0C5E0.png

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Just walking home and it is remarkably humid! Makes sitting outside tonight for any approaching storms a mossie party fest! Uurrgghhh!!!

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47 minutes ago, Alderc said:

About now, all I see is showers and a broad area of rain.

i spy with my little eye something beginning with B......

Top trolling nothing expected to develop until 21z

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2 minutes ago, Harry said:

In addition to Nick F’s forecast, PJB (UKWW) has updated his thoughts for this evening:

 

Update 18:00 BST 

No Changes to earlier Risk Zones but increased to 90% Risk and added a zone of most impact. 


Detail 

Afternoon Temperatures over France in the Paris region have reached around 30-31C, The air lifted here too dry and subsided to produce significant convection. The trajectories at 950mbs / 925mbs take this very warm air westwards towards an area of 925mb confluence to an area to the South of the Cherbourg Peninsula. This area of enhanced confluence just aloft will be enough to initiate convection in a few hours time. At the present aloft there is an area of decreasing positive earth vorticity advection moving NNE from a SSW direction across extreme Northern France and England and Wales. This largely responsible for the decreasing mid level ascent and the clouds thinning and breaking. To the South over Biscay an area of increasing Positive earth vorticity advection is located between 47.5N and 42N and is responsible for the increase in convection over the Bay of Biscay. There is also an area of shear vorticity in the flow and over N Spain a shear axis. During the day the plume of high theta -w has advected northwards across France and the storms will fire in the zone of greatest 850mb moisture and heat for the air rising within the confluence zone to the South of Cherbourg. So we have Southerly flow at 850mbs, easterly flow at 925mbs meeting Northerly flow at 950mbs, and a cooling and increasing spinning environment aloft above 700mbs. This combination of low level confluence, 850mb moisture and cooling and increasingly active kinematic environment aloft will allow for storms to grow rapidly once they form. The 12Z Models are in good agreement in taking the multi-cells to the NE over English Channel - routed to nr 900-920mbs with the perfect 850mb airflow to sustain inflow and to grow daughter cells on the south and south east of the growing organised storm complex. As the storms grow the divergence aloft from the right entrance to a SW Jet stream aloft over Biscay and the increasing positive earth vorticity will allow for outflow to be taken North east wards away from the storms and into another small scale jet over the Central North Sea. Therefore the atmospheric chimney is effectively setting up very nicely for some very active cells indeed to move NE. Supercells are possible as the system grows and there is the added low level confluence to add to further storms which develop over and up the M11 towards the Wash during the latter part of the night, due to some further increase in the low level confluence and a greater amount of upper level divergence and a slight increase in the upper level kinematics over this region during the 03Z to 06Z on Tuesday. Area should be considered to have increase low level helicity and possible super cellular tornado possibilities. (PROB 20-25%) 

Very high rainfall rates of 80/150mm/h are likely as the zone moves North . The French AROME Model somewhat further east with its precipitation field. However there is good agreement from the Dutch Hirlam, ICON, ARPEGE and UKMET 2KM in the zone from Sussex and East Hants, up across Surrey and across Central London and then up the M11 towards Cambridge and the Wash. Frequent Lightning, Flooding and Hail are possible. The small but not negligible risk of Tornado activity later in the period is mentioned above 

Disruption and delays to the Travel Network are extremely likely as well as the power network.  

OVERALL RISK ASSESSMENT IS NOW RAISED TO 90% for the areas mentioned above and in the graphic.

Attached thumbnail(s)

F54928A9-29C8-4DE6-BB4B-7EEF64D0C5E0.png

Beat me to it 😄

I’m headed to Tonbridge shortly. Want to be in the hatch

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Looks like i will be going up Firle beacon tonight.

Top viewing point in my opinion. 

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4 minutes ago, Harry said:

In addition to Nick F’s forecast, PJB (UKWW) has updated his thoughts for this evening:

 

Update 18:00 BST 

No Changes to earlier Risk Zones but increased to 90% Risk and added a zone of most impact. 


Detail 

Afternoon Temperatures over France in the Paris region have reached around 30-31C, The air lifted here too dry and subsided to produce significant convection. The trajectories at 950mbs / 925mbs take this very warm air westwards towards an area of 925mb confluence to an area to the South of the Cherbourg Peninsula. This area of enhanced confluence just aloft will be enough to initiate convection in a few hours time. At the present aloft there is an area of decreasing positive earth vorticity advection moving NNE from a SSW direction across extreme Northern France and England and Wales. This largely responsible for the decreasing mid level ascent and the clouds thinning and breaking. To the South over Biscay an area of increasing Positive earth vorticity advection is located between 47.5N and 42N and is responsible for the increase in convection over the Bay of Biscay. There is also an area of shear vorticity in the flow and over N Spain a shear axis. During the day the plume of high theta -w has advected northwards across France and the storms will fire in the zone of greatest 850mb moisture and heat for the air rising within the confluence zone to the South of Cherbourg. So we have Southerly flow at 850mbs, easterly flow at 925mbs meeting Northerly flow at 950mbs, and a cooling and increasing spinning environment aloft above 700mbs. This combination of low level confluence, 850mb moisture and cooling and increasingly active kinematic environment aloft will allow for storms to grow rapidly once they form. The 12Z Models are in good agreement in taking the multi-cells to the NE over English Channel - routed to nr 900-920mbs with the perfect 850mb airflow to sustain inflow and to grow daughter cells on the south and south east of the growing organised storm complex. As the storms grow the divergence aloft from the right entrance to a SW Jet stream aloft over Biscay and the increasing positive earth vorticity will allow for outflow to be taken North east wards away from the storms and into another small scale jet over the Central North Sea. Therefore the atmospheric chimney is effectively setting up very nicely for some very active cells indeed to move NE. Supercells are possible as the system grows and there is the added low level confluence to add to further storms which develop over and up the M11 towards the Wash during the latter part of the night, due to some further increase in the low level confluence and a greater amount of upper level divergence and a slight increase in the upper level kinematics over this region during the 03Z to 06Z on Tuesday. Area should be considered to have increase low level helicity and possible super cellular tornado possibilities. (PROB 20-25%) 

Very high rainfall rates of 80/150mm/h are likely as the zone moves North . The French AROME Model somewhat further east with its precipitation field. However there is good agreement from the Dutch Hirlam, ICON, ARPEGE and UKMET 2KM in the zone from Sussex and East Hants, up across Surrey and across Central London and then up the M11 towards Cambridge and the Wash. Frequent Lightning, Flooding and Hail are possible. The small but not negligible risk of Tornado activity later in the period is mentioned above 

Disruption and delays to the Travel Network are extremely likely as well as the power network.  

OVERALL RISK ASSESSMENT IS NOW RAISED TO 90% for the areas mentioned above and in the graphic.

Attached thumbnail(s)

F54928A9-29C8-4DE6-BB4B-7EEF64D0C5E0.png

Literally bang in the middle of the hatch - just wet myself!

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DAMN! That is sounding very noteworthy indeed!

HERE'S TO AN AMAZING ALL-NIGHTER T-STORM EVENT!

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Just now, Flash bang flash bang etc said:

Beat me to it 😄

I’m headed to Tonbridge shortly. Want to be in the hatch

Good luck @Flash bang flash bang etc Very much hope it’s worth the journey! Don’t forget your insect repellant 😂 given current models (and PJB’s hatched zone) there is little point in me going anywhere - that said the 12z ARÔME would see me largely getting nothing! I’ll take my chances though and keep my fingers crossed 

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Hard to imagine when you look across Northern France that severe thunderstorms are expected, but they are. I will be heading out chasing shortly. Due to the fact that storms will be moving NNE across the Channel and then cutting a swathe straight through part of the UK I no longer feel the need to go all the way to the south coast, at least not initially. My plan is to head down the M1 to get into Luton around 9pm by which time I am hoping cells will have fired across France. Once this happens I will have a better idea where to go. I will either stay put or head south to the M25 where I can go either east or west.

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