Convective / Storm Discussion Thread - 31st May 2017 onwards

[A.J]

19 minutes ago, East_England_Stormchaser91 said:

Do you think something similar to June 2012 is possible? Given the potential energy? I've never seen SB cape in the UK that high before, ever. 

to aid comparison, here are a few links that will help

http://www.stratusdeck.co.uk/28th-june-2012

from Estofex

"Storm Forecast

Valid: Thu 28 Jun 2012 06:00 to Fri 29 Jun 2012 06:00 UTC

Issued: Wed 27 Jun 2012 22:28

Forecaster: GATZEN

A level 2 was issued for the Benelux countries mainly for large hail and severe wind gusts.

A level 1 was issued for portions of the northern British Isles mainly for tornadoes.

A level 1 was issued for the central and southern British Isles mainly for large hail.

SYNOPSIS

An Atlantic trough moves into western Europe pushing a ridge into central Europe. An elevated mixed layer currently across France will spread north-eastward on Thursday, and rich boundary-layer moisture is expected underneath the cap from eastern France to eastern England and the Benelux countries. Over eastern Europe, rather cool/dry air will remain.

DISCUSSION

The Benelux region

The nose of the warm low-level air will move into the Benelux countries ahead of the surface cold front. Moisture pooling and diurnal heating will result in CAPE around 2000 J/kg given the elevated mixed layer spreading northward. Additionally, strong vertical wind shear will be in place.

Favorably veering profiles and rather isolated convection in the afternoon hours pose a threat of supercells capable of producing large or very large hail and maybe a tornado. Later in the period, a linear MSC may develop ahead of the cold front. The increasing low-level jet is forecast to increase the potential of severe wind gusts with this MCS that will spread into western Germany. Excessive rain is also not ruled out.

British Isles

Warm air advection will continue during the night and morning hours from England into Scotland. This warm air is characterized by steep mid-level lapse rates. The warm air advection will increase, and a low-level jet is expected to strengthen on Thursday ahead of the approaching cold front.

Latest satellite images indicate widespread convective/stratiform clouds spreading eastward ahead of the approaching trough and associated jet streak. Until the morning hours, these clouds will spread across much of the forecast area. During the day, especially the southern portions will be placed below the anticyclonic flank of the approaching jet streak, and weak forcing may result in rather strong daytime heating.

Furthern north, QG forcing will be stronger. Elevated storms in the warm air advection regime may root to the boundary-layer in the noon and afternoon hours. Storm motion vectors close to the cold front are expected to result in a squall line with excessive rain the main threat. The severe wind threat is expected to be rather low given the expected slow propagation of the squall line.

Further north, storms are expected to be more isolated. Although instability will be weak, these storms may organize given strong vertical wind shear. Mesocyclones will pose a threat of tornadoes.

Across the southern British Isles, weak QG forcing will remain through-out the period. Along the cold front, some storms may evolve especially during the the second half of the day, when low-level heating and rather rich moisture will result in CAPE of 1000 J/kg. Strong vertical wind shear will overlap with this instability, and storms that form will rapidly organize. The potential of supercells is expected to decrease from the west during the day, and mostly multicells are forecast, capable of producing large hail and strong to severe wind gusts. However, supercells are not ruled out especially across the eastern portions where larger hodographs will persist well into the afternoon hours ahead of the cold front. Isolated very large hail may be possible when supercells indeed will form. The convective activity will decay during the evening hours in the wake of the surface cold front."

From Dan at convective weather (UKASF as it then was)

Severe

Forecaster: Dan

Last Updated: 2012-06-27 21:58:00

Valid: 2012-06-28 00:00:00 - 2012-06-28 23:59:00

Areas Affected:

SVR: SE Scotland/Borders, NE Eng, Yorkshire, E Mids, East Anglia

MDT: NE Eng, Yorkshire, E Mids, N Cambs/W Norfolk

SLGT: Majority of United Kingdom, excluding NW Highlands and N Isles

Synopsis:

Upper trough gradually approaches from the west, allowing a plume of high WBPT and very high ThetaE to advect northwards across Britain. Destabilisation will occur on the plume axis during the passage of a pronounced shortwave trough, with potential for severe convection over Lincolnshire, Cambridgeshire and Norfolk during the afternoon.

Discussion:

Several areas of interest exist during this forecast period, with varying levels of severity.

From the start of the forecast period through to daylight, indications are that elevated thunderstorms will develop over the English Channel/move northwestwards from northern France as the moisture plume destabilises with the approach of a shortwave. These mid-level showers/storms will tend to merge as they cross SW England and across the Irish Sea to Ireland. >40kts DLS coupled with >25kts would suggest some organisation of such storms into multicells or elevated supercells, sustaining such storms for quite a long period of time.

>800J/kg MLCAPE also highlights reasonably frequent lightning with these storms at first, although the exact interaction of such storms with long sea tracks leaves us with a cautious SLGT level for sferic coverage for the time being - this may be upgraded to MDT if necessary. Other than very heavy rain, with PWAT values near 36mm locally, generally due to the elevated nature of storms severe weather is unlikely.

This general area of thundery rain will then move north across the Irish Sea, grazing both Ireland/Northern Ireland and western parts of Britain during the day on Thursday, with ever-decreasing values of MLCAPE. Nevertheless, it is quite probable that lightning activity will continue throughout the day as cells remain sustained with decent shear available.

Across the rest of England and Wales, a few mid-level showers will migrate northwards later in the night and first thing Thursday morning, although significant WAA in the mid-levels will provide strong capping, thus most showers will be light with a low probability of thunder/lightning. Capping is strongest towards SE England, and weaker towards the NorthWest.

Behind these showers, conditions should improve with some patchy insolation expected as cloud cover begins to break. Dewpoints of ~17C and surface temps of 22-27C are simulated by most models, and will be substantial enough to generate some surface-based convection.

Initially this will take place over eastern England, east of the Pennines with the plume axis and approach of a shortwave, combined with topographical forcing. Initially numerous thunderstorms are forecast to develop from ~12z onwards, with forecast soundings suggesting ample shear (typically 40kts DLS, 30kts LLS) and some helicity (>300m^2/s^2). This would generate an environment, coupled with 1000-1300J/kg CAPE, capable of producing multicells or supercells, with the potential for a tornado.

However, due to the weakly-capped environment it is likely that mass forced ascent will quickly merge such storms into a linear formation along the trough, eventually forming an MCS producing frequent lightning and possibly some large hail (locally >3cm). PWAT of up to 39mm also increases the risk of flooding from torrential downpours.

This line will continue to move quickly northeastwards, wrapping back into eastern Scotland during the evening so increasing sferic activity is expected here during the evening.

It is not clear where the southeastern edge of such line will be, with some inter-model disagreements. Current thinking is south Lincolnshire southwards will be in a more-capped environment, and here such storms that develop will be more scattered and less likely to merge into any linear structures. Indeed, by adjusting forecast soundings to realistic T and Td values, 1800-2000J/kg CAPE is potentially available, with a slight cap being broken by combination of rising LSTs and the approach of a shortwave.

Thus, in a zone from northwest Essex to southern Lincolnshire, a few scattered surface-based thunderstorms are expected to form in the early-mid afternoon hours, rapidly moving northeastwards. Given such CAPE values, combined with >40kts DLS, >25kts LLS and >250m^2s^-2 helicity, then a few discrete supercells are possible, especially in southern Lincolnshire across The Fens to West Norfolk.

Veering wind profiles with height, and a substantial increase in speed shear with height suggest the potential for one or two severe thunderstorms, with rotating mesocyclones. With forecast dry air aloft, such storms will be capable of producing hail 3-4cm in diameter (up to golf ball), frequent lightning, with local flooding possible given PWAT values approaching ~40mm, although fast storm-motion should ease this risk somewhat. If the cap can be broken to generate such storms, then this is borderline our threshold for EXTRMLY SVR. Low LCLs as a result of relatively low dewpoint depressions (generally ~7C) with such shear values poses a significant tornado risk. Convective gusts may be as high as 50-60mph, and outflow boundaries may pose a focus for breaking the cap downstream and generating new cells.

Storms will rapidly move northeastwards, generally clearing by 18z.

In SE England, capping appears to be too strong, and the surface flow not backed enough, to generate any noteworthy convection, although some uncertainty remains."

 

hope those links and descriptions help!

[Eye to the sky]

3 minutes ago, whoissean said:

I live near the white area of the map very interesting to see it's been a touch cooler here today and overcast murky skies. 

Hi Whoisseen.I've lived Just north of Derby all my life and can remember some cracking storms in the mid to late 90's.The last 10 years or so though have seen a spectacular decline in storm activity around my area and I don't know why.I've a 3 year old son and he has yet to see a decent storm.Currently in Mablethorpe on holiday and it is overcast and cool.

[Mark Griffin]

Well i'm under all that cloudy crap in Yorkshire and it's 17.5c.  Very humid though

[IMP757]

9 minutes ago, ajpoolshark said:

to aid comparison, here are a few links that will help

http://www.stratusdeck.co.uk/28th-june-2012

Not seen this before. Really interesting read, thanks for posting!

[P-M]

1 minute ago, IMP757 said:

Not seen this before. Really interesting read, thanks for posting!

This storm was a monster.  I seen walls collapse and streets turned in to rivers it was amazing / scary at the same time.  I work for a housing company and two of our houses were struck by lightning and burned to the ground.  So much respect is needed for these weather events but I love seeing them unfold (obviously not the damage) but the light display was amazing I have never seen anything like it.

[IMP757]

1 minute ago, P-M said:

This storm was a monster.  I seen walls collapse and streets turned in to rivers it was amazing / scary at the same time.  I work for a housing company and two of our houses were struck by lightning and burned to the ground.  So much respect is needed for these weather events but I love seeing them unfold (obviously not the damage) but the light display was amazing I have never seen anything like it.

Am I right in saying on that day there were two storm systems at once, one which moved north easterly from Birmingham area through Lincolnshire whilst the other moved north easterly from Manchester towards Newcastle area?

[East_England_Stormchaser91]

38 minutes ago, Supacell said:

I am hoping something similar to 9th June 2014 happens on Thursday as I am staying directly under the path that huge supercell took

You're going to be in for something special according to estofex. Already an advanced forecast in place for Germany! 

Road networks are much better over there too, and speeding in many areas of their motorways is perfectly legal! Enjoy it and make the best of it supa. 

[P-M]

Just now, IMP757 said:

Am I right in saying on that day there were two storm systems at once, one which moved north easterly from Birmingham area through Lincolnshire whilst the other moved north easterly from Manchester towards Newcastle area?

 

I think so yes.  The one that moved over my area I tracked from around Blackpool / Preston ish area and watched it blow.  It was the rainfall that was unprecedented up this way - I have never seen so much rain fall at once.  But I remember some intense storms earlier on further south so that sounds about right.

[toggerob]

2015 stands out immediately in my mind with the July 1st supercell, watching it roll in from the Goyt Valley and across Cheshire with lightning crashing around every few seconds and being fortunate to be in-situ along the southern dry-side so all the structure was evident. Even 2 hours after it had passed and moved up into Yorks/Lancs the lightning was still flicking away across the anvil on the northern horizon.

 

[IMP757]

1 minute ago, P-M said:

 

I think so yes.  The one that moved over my area I tracked from around Blackpool / Preston ish area and watched it blow.  It was the rainfall that was unprecedented up this way - I have never seen so much rain fall at once.  But I remember some intense storms earlier on further south so that sounds about right.

I remember it all kicking off that day but it was before I really took an interest in the weather, so I thought nothing of it at the time unfortunately. Only looking back on it now do I realise what actually happened and the severity of it! 

[P-M]

Just now, IMP757 said:

I remember it all kicking off that day but it was before I really took an interest in the weather, so I thought nothing of it at the time unfortunately. Only looking back on it now do I realise what actually happened and the severity of it! 

Anything close to that day and I'll be happy *minus the damage* but wow what a storm.  Thinking back I remember two lots coming through in short time.  here's the news from the night:

 

 

 

 

[Delka]

2 hours ago, Nick F said:

Storm & Convective Forecast

Issued 2017-06-20 12:03:56
Valid: 20/06/17 12z to 22/06/17 06z

DAYS 1 & 2 CONVECTIVE / STORM FORECAST - TUES 20TH & WEDS 21ST JUNE

Synopsis

An upper high which has persisted over southern Britain over recent days will begin to weaken and retreat SE during the rest of this week, as an upper trough approaches and moves in across western Britain by early Thursday. A surface high will drift east across northern Britain on Tuesday, pushing a weakening boundary southwards across England and Wales, separating hot and humid air to the south and cooler and fresher conditions to the north currently over Scotland. Surface convergence to the south of this boundary moving south may, with heating, trigger a few isolated afternoon storms. The same boundary will stall late Tuesday before drifting north as a warm front across northern Britain Tuesday night and through Wednesday, warm and humid plume returning north across below this warm front will likely destabilise across northern Britain early Wednesday, then further south later in the day.

DAY 1 CONVECTIVE FORECAST

Valid: Tuesday 12z to Wednesday 06z

… WALES, MIDLANDS …

Although forecast isolated storm development failed to materialise over last few days across England and Wales due to stout cap caused by upper high and warm/dry profiles, continued weakening of heights and slight cooling aloft from the NW in tandem with surface breeze convergence just to the south of boundary shifting south and stalling may breach the stout cap to allow a few isolated thunderstorms. Should a storm develop, it will tap into a reservoir of hot and humid air with CAPE values forecast in the order of 1000-1500 j/kg CAPE. High rainfall totals in a short-space of time leading to localised flooding with be the main threat from any storm that does develop, given high PWAT (Precipitable Water) values of 30-36mm pooling along convergence zones. High CAPE may also support sufficient buoyancy for isolated large hail too, though limited by lack of any appreciable vertical shear. Despite favourable parameters for storms, there are doubts that upper ridging will weaken enough to allow storms to develop, like last few days, so have refrained from severe probabilities for now.

… N. IRELAND, N ENGLAND and S SCOTLAND …

A shortwave trough moving NE on forward side of long wave trough approaching Ireland will likely cause large scale ascent of warm/moist conveyor returning north across the UK/EIRE Tuesday night, leading to an increase in mid-level convection and eventually the development of elevated thunderstorms by 06z Wednesday 30-50 knot SWly flow at 500mb and 30-40 knot 0-6km effective shear will support storm organisation into clusters, capable of isolated large hail, high rainfall totals leading to localised flooding, gusty winds and frequent cloud-to-ground lightning. Have issues a MARGINAL risk for severe weather across N England and Scotland.

DAY 2 CONVECTIVE FORECAST

Valid: Wednesday 06z to Thursday  06z 

… N IRELAND, far N of ENGLAND and SCOTLAND …

Elevated thunderstorms are likely to be ongoing across N. Ireland, N England and Scotland during the morning with further storms perhaps developing through the day and moving NE, though they will be hit and miss in nature. Like the day 1 forecast, storms will be capable of hail, gusty winds and frequent lightning, though high rainfall totals leading to localised flooding will be main threat. Have carried over MARGINAL risk of severe weather before storms eventually clear east into the N Sea Wednesday evening.

… N ENGLAND, MIDLANDS and E ENGLAND …

Some elevated thunderstorms may be ongoing in the morning across the far north of England in association with destabilisation of warm moist plume returning north and destabilising across northern Britain as per forecast above, this activity clearing by afternoon. GFS and ECM forecast a highly unstable hot and humid airmass in place across much of England and Wales on Wednesday afternoon, with CAPE values in the order of 1000-2500 j/kg. Again, there is uncertainty whether the strong cap created by upper high across the south and EML (Elevated Mixed Layer) aloft will weaken, however with temperatures reaching 33C inland across central England, weakening heights and strengthening divergent winds aloft, along with weak surface trough moving east across central and northern UK creating convergence coupled with orographic lift, there may be sufficient forcing to break the cap to allow a few thunderstorms to develop across the southern Pennines, Midlands and parts of E England. Strengthening 500mb SWly flow aloft reaching 40-50 knots along with 30-40 knots of effective 0-6km shear suggests any storms that develop will quickly organise … with scope for a supercell or two … capable of producing large hail (1-2 inches), damaging wind gusts, flash flooding and frequent cloud-to-ground lightning. Also, likely discrete nature of storms and forecast strong storm-relative helicity may favour the development of tornado. However, given uncertainties of convective initiation in this region and isolated nature if storms do develop, have refrained from issuing more than a SLIGHT risk of severe weather for now, but may upgrade with the DAY 1 outlook update, if initiation looks more probable and widespread in one area.

... WALES and SW ENGLAND ... 

Later in the night until end of forecast at 06z Thurs, models indicate another round of thunderstorms, mostly elevated, forming along developing cold front shown on fax charts across Wales and SW England. These storms may bring a risk of torrential rain leading to flash-flooding.

surprising to be placed in the SLIGHT zone when every other forecast and warning etc has me out of any action!

[Flash bang flash bang etc]

Cell developing over South Wales and a convergence zone along the north of the M4 by the looks of things...

[Allseasons-Si]

14 minutes ago, SNOW_JOKE said:

2015 stands out immediately in my mind with the July 1st supercell, watching it roll in from the Goyt Valley and across Cheshire with lightning crashing around every few seconds and being fortunate to be in-situ along the southern dry-side so all the structure was evident. Even 2 hours after it had passed and moved up into Yorks/Lancs the lightning was still flicking away across the anvil on the northern horizon.

 

Yes i remember that one well,i was sat right on the edge of it on woodhead pass and was looking strait above me,i did have a sure neck after a while,i had my camera on me but the battery had died of death and was really guttered that i did not capture this beauty,i am glad some other folk including you got this footage

oh!!!,i forgot to mention that i booked that day off on the afters shift to attend a funeral that morning,at least i got to whitness the storm.

Edited June 20, 2017 by Allseasons-si

[LightningLover]

Has anyone noticed the cells across N France?

[Thunderstruck]

Well good luck, everybody. I hope you enjoy a nice storm, but spare a thought for us in the SE as we suffer another swelteringly sleepless night!

[weirpig]

I've seen worse potential 

[LightningLover]

[Arnie Pie]

yom doft @weirpig

 

Edited June 20, 2017 by Arnie Pie

[Delka]

Just now, LightningLover said:

preview of whats to come for some on thursday?

[LightningLover]

2 minutes ago, Delka said:

preview of whats to come for some on thursday?

Let's hope so!

[Flash bang flash bang etc]

I'm interested in the clouds popping up and travelling out of Wales...

Did someone mention 5pm as an initiation time?

[StormChaseUK]

18z-21z  last night the best convection seemed to be 7-9pm

[Dangerous55019]

In the past half hour the heat and humidity have suddenly gone through the roof!! 

The sky has gone from a milky blue to a grey/hazy orange colour... The sweat is now pouring off me.

Please let this be the start the cap breaking and allowing it to go bang. 

[Dangerous55019]

Just managed to grab a photo of what the sky is like here at the moment... It's really oppressive.