Convective/Storm Discussion Thread - 1st August onwards

[Mokidugway]

3 minutes ago, Mapantz said:

Yeah, looks like it. Nothing like that showing on the MR version. The CAPE just vanishes on the SR.

Is data  glitch the new name for HP supercells mumspantz ?? 

Edited April 20, 2018 by Mokidugway

[Mapantz]

2 minutes ago, Mokidugway said:

Is data  glitch the new name for HP supercells mumspantz ?? 

HP laptops

[Ben Sainsbury]

7 minutes ago, Mapantz said:

Yeah, looks like it. Nothing like that showing on the MR version. The CAPE just vanishes on the SR.

I always thought a thunderstorm of a large intensity, could effectively “use up” the atmospheric CAPE?

[Cheshire Freeze]

Tony Gilbert over on ukww seems to think HP might be too prominent tomorrow for much to break out. 

[Mokidugway]

1 minute ago, CreweCold said:

Tony Gilbert over on ukww seems to think HP might be too prominent tomorrow for much to break out. 

Aye to quote Damis favourite band ,it's a CIN ........

[Chris.R]

The WRF 12Z  is showing some  great values for my location tomorrow evening. At 18Z: 1645 J/kg SBCAPE and -5 LI with 23 kts DLS. Also modest MUCAPE continues into the early hours. Those are figures more worthy of high summer. Looks like a surface low to my South in the early hours of Sunday which could be interesting. No sign of much CIN except near sunset. 

Edited April 20, 2018 by Chris.R

[Flash bang flash bang etc]

Hmmm methinks it’s another case of a long build up to a non-event with lots of teasing along the way.

Too many times the high pressure is just too dominant and there isn’t enough surface warming once the morning cloud (and potential fog?!) clears.

Will keep an eye toward wales and the west just in case but it’s looking like it’s all being downgraded to nothing. First disappointing plume setup of the year? ...Perhaps!

But wait! My eye is drawn to the overnight potential in the SE regions which looks more possible given the synoptics currently being offered.

We will see tomorrow! The wait continues...

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Sat 21 Apr 2018 - 05:59 UTC Sun 22 Apr 2018

ISSUED 18:44 UTC Fri 20 Apr 2018

ISSUED BY: Dan

... SATURDAY MORNING ...

Elevated showers and a few thunderstorms may develop on Saturday morning over the English Channel and drift north, as high ThetaW airmass advects from France into S / SW England and begins to destabilise. There is some uncertainty as to how much destabilisation may take place at this stage of the day given only subtle forcing, and then the exact track of such storms given large model guidance spread - generally Devon and Dorset, but perhaps as far east as West Sussex and as far west as Cornwall. Any storms that do form will track to the N or NW with time, into S Wales / SW Midlands by late morning/midday, though possibly with a weakening trend. Initially, precipitation may not reach the ground due to very dry air through depth, though subsequent showers will help moisten the column with time.

 

... SATURDAY AFTERNOON ...

A complex picture, with ongoing elements of elevated convection drifting north associated with plume axis across Wales and the Midlands. Forecast profiles exhibit a capping warm nose around 850-900mb; however, provided there are enough cloud breaks to provide sufficient insolation, then there is scope to erode this cap and allow surface-based thunderstorms to develop. The focus is primarily over N + E Wales, N + NW Midlands into northern England, aided by developing low-level wind convergence and orographic forcing. This very much dependent on how much mid/upper level cloud will be present from earlier elevated convection approaching from the south. Initiation may be quite late in the afternoon and into the evening hours, when better forcing arrives. Uncertainty also exists over the north/south position of areas that may be affected, and the MDT issued may need to be adjusted southwards, depending on trends. Shear is a little on the weak side, but given the degree of potential instability (800-1,200 J/kg CAPE) hail up to 2.0cm in diameter will be possible from any stronger thunderstorms, along with frequent lightning, gusty winds (40-50mph) and some localised surface water flooding given 25-30mm PWAT.

 

... SATURDAY EVENING / NIGHT ...

Stronger forcing will arrive during the evening hours as the Atlantic upper trough approaches from the W - this will likely result in an increasing coverage of (mostly elevated) thunderstorms as the ThetaW plume continues to destabilise. This will happen in a rather sporadic fashion along an eastward-advancing N-S orientated line, and hence difficult to pinpoint exact areas where thunderstorms are most likely to occur. There is some model agreement for thunderstorms to erupt over the English Channel and drift NE across areas from Hampshire eastwards to Kent - given the magnitude of instability, lightning will be frequent with any thunderstorms that do develop, with the potential for some hail from the strongest cells. However, due to the uncertainty in coverage of thunderstorms have refrained from issuing a MDT for now, but one may be introduced if confidence improves a little. It is possible some thunderstorms could develop as far north as E/SE Scotland, or at least offshore from there over the North Sea.

 

http://www.convectiveweather.co.uk/forecast.php?date=2018-04-21

Edited April 20, 2018 by Summer Sun

[Harry]

2 hours ago, John Hodgson said:

Caught sight of some mid level convection with a pileus cap about half an hour ago towards the east. Seems to have collapsed now though. 

My first time on in 2018! Hello all.

Agreed @John Hodgson I too saw some lovely mid level convection, some localised Ac fields and late evening some more pronounced convection. Definitely felt more humid today (I think so anyway).

Hopeful for tomorrow - got my fingers crossed! As often is the case I suspect it’ll be a now casting scenario rather than anything concrete. Am down in Dymchurch this weekend so hopeful for some clippers

Edited April 20, 2018 by Harry

[Summer Sun]

Storm Forecast
Valid: Sat 21 Apr 2018 06:00 to Sun 22 Apr 2018 06:00 UTC
Issued: Fri 20 Apr 2018 20:32
Forecaster: TASZAREK

A level 1 was issued for NW France and S United Kingdom mainly for large hail, severe wind gusts and excessive precipitation.

...N France and S United Kingdom...

Under strong diurnal heating, ~ 10 g/kg mixing ratios and ~ 7 K/km mid-level lapse rates ML CAPE develops up to 1500-2000 J/kg. Although lifting mechanism is not prominent, a belt of weak PVA should help to trigger thunderstorms in the afternoon hours. Within the support of moderate instability and ~ 15 m/s DLS, convective cells should evolve into multicell clusters capable of producing severe wind gusts and excessive precipitation. Small chances for supercells may also provide few large hail events, especially given steep lapse rates in mid-levels. It is expected that thunderstorms will maintain their lightning activity until nighttime hours and move NEwardly.

http://www.estofex.org/cgi-bin/polygon/showforecast.cgi?text=yes&fcstfile=2018042206_201804202032_1_stormforecast.xml

[Hodgheg]

12 minutes ago, Harry said:

My first time on in 2018! Hello all.

Agreed @John Hodgson I too saw some lovely mid level convection, some localised Ac fields and late evening some more pronounced convection. Definitely felt more humid today (I think so anyway).

Hopeful for tomorrow - got my fingers crossed! As often is the case I suspect it’ll be a now casting scenario rather than anything concrete. Am down in Dymchurch this weekend so hopeful for some clippers

Indeed it was more humid. I don't know if anyone else has commented on this but yesterday the humidity was only around 35% according to the Heathrow METAR yesterday. Thats quite unusual as far as a can see from my very amateur observations.  I shall be glued to the radar from about 3 pm onwards tomorrow. To reduce the stress i have made some changes for myself this summer.  1. I wont be looking at every single GFS run leading up to a possible event. I realise i don't have enough knowledge to be able to discern anything myself anyway and I'll leave it up to those with more expertise.  2. Im going to unfollow twitter and facebook pages that hype up events and promise supercells in every damn forecast!

[Harry]

8 minutes ago, John Hodgson said:

Indeed it was more humid. I don't know if anyone else has commented on this but yesterday the humidity was only around 35% according to the Heathrow METAR yesterday. Thats quite unusual as far as a can see from my very amateur observations.  I shall be glued to the radar from about 3 pm onwards tomorrow. To reduce the stress i have made some changes for myself this summer.  1. I wont be looking at every single GFS run leading up to a possible event. I realise i don't have enough knowledge to be able to discern anything myself anyway and I'll leave it up to those with more expertise.  2. Im going to unfollow twitter and facebook pages that hype up events and promise supercells in every damn forecast!

Haha yeah I tell myself that every year... never happens! Every GFS and WRF-NMM run I’m 

Loving the estofex forecast - just hope it materialises 

[Darren Bown]

Here’s Convective Weather’s risk map for tomorrow. They got the last few storm risks correct.

[Darren Bown]

Estofex risk. 50% lightning and a level 1 across central and southern England and eastern wales

 

.N France and S United Kingdom...

Under strong diurnal heating, ~ 10 g/kg mixing ratios and ~ 7 K/km mid-level lapse rates ML CAPE develops up to 1500-2000 J/kg. Although lifting mechanism is not prominent, a belt of weak PVA should help to trigger thunderstorms in the afternoon hours. Within the support of moderate instability and ~ 15 m/s DLS, convective cells should evolve into multicell clusters capable of producing severe wind gusts and excessive precipitation. Small chances for supercells may also provide few large hail events, especially given steep lapse rates in mid-levels. It is expected that thunderstorms will maintain their lightning activity until nighttime hours and move NEwardly.

Edited April 20, 2018 by Darren Bown

[Hodgheg]

4 minutes ago, Darren Bown said:

Here’s Convective Weather’s risk map for tomorrow. They got the last few storm risks correct.

In terms of storms what i'm most interested in is the frequency of the lightning. Do you know if most of these forecast include lightning rate as a measure of severity? 

Edited April 20, 2018 by John Hodgson

[BlueHedgehog074]

If Convective Weather’s storm risk map for tomorrow proves accurate, then it looks like for the Midlands area anyone to the North/West of my house could see a storm, while anyone to the South/East of my house may not see one. ?⚡️

Edited April 20, 2018 by DiagonalRedLine

[Flash bang flash bang etc]

4 minutes ago, Darren Bown said:

Here’s Convective Weather’s risk map for tomorrow. They got the last few storm risks correct.

Don’t like to contradict anyone but CW has predicted about 7 days of storms which didn’t materialise in the last month or so.

Not to say they were wrong - but don’t take it as gospel these storms will do as they like!

[Harry]

12 minutes ago, DiagonalRedLine said:

If Convective Weather’s storm risk map for tomorrow proves accurate, then it looks like for the Midlands area anyone to the North/West of my house could see a storm, while anyone to the South/East of my house may not see one. ?⚡️

Que???

Surely the map suggests anything east of Belfast, Glasgow and Inverness COULD see a storm???

[Mokidugway]

Highly unlikely Kent will get anything from this set up 

[Nick F]

Storm & Convective Forecast

Issued 2018-04-20 22:07:48
Valid: 21/04/2018 6am TO 22/04/2018 6am

THUNDERSTORM OUTLOOK - DAY 1 (SATURDAY 21ST APRIL)

Synopsis

An upper trough moving across the Atlantic will arrive across the far west of the British Isles on Saturday, as upper level high on near continent retreats. A surface low will drift NE to the south of Iceland beneath the upper trough arriving to the west. Backing of the flow to a Sly direction across England and Wales on Saturday will draw in an increasingly warm and moist but unstable airmass out of France, with an increasing risk of thunderstorms developing northeastwards across England and Wales during the forecast period.

… ENGLAND and WALES …

* Risk of ...

hail (isolated large)

strong wind gusts

flash-flooding

frequent cloud-to-ground lightning

Plume of warm moist air, characterised by high wet bulb potential temps (WBPT), will advance across S England and Wales Saturday morning, a shortwave trough moving up from NW France looks to destabilise this plume and support the development of thundery showers and increasingly a risk of elevated thunderstorms moving N/NE, initially isolated across SW and S central England in the morning, then more widely across Wales, Midlands and parts of N England into the afternoon, as mid-level temperatures continue to cool aloft from the west, steepening lapse rates. These elevated storms may bring some hail, frequent lightning and localised flooding.

Although there will be some capping of the surface airmass by the Elevated Mixed Layer of the plume, surface heating combined with orographic forcing and/or breeze convergence may allow the cap to be overcome to allow some surface-based thunderstorms to develop where skies clear – particularly over north Wales, north Midlands and northern England. Any surface based storm that develops could tap into 500-900 j/kg CAPE – which could allow some isolated large hail, torrential rain leading to flash-flooding, frequent CG lightning and strong winds gusts … the weak vertical shear (20-30knts between 0-6km) will limit severe potential, so will abstain from delineating a severe risk area.

During the evening, increasing large scale ascent and cooling aloft from approaching Atlantic trough from the west interacting with WBPT plume advecting north is forecast by a number of models to form a wave of elevated storms developing over the English Channel / N France initially before spreading northeast across parts of S and SE England along with E Anglia in the evening and overnight. Also ongoing storms further north over the Midlands and N England for a time, before clearing NE in the night. These elevated storms may produce hail, strong wind gusts, localised flooding and frequent cloud-to-ground lightning.

Issued by: Nick Finnis

https://www.netweather.tv/weather-forecasts/uk/convective

Edited April 20, 2018 by Nick F

[Ben Sainsbury]

16 minutes ago, Flash bang flash bang etc said:

Don’t like to contradict anyone but CW has predicted about 7 days of storms which didn’t materialise in the last month or so.

Not to say they were wrong - but don’t take it as gospel these storms will do as they like!

You aren't wrong, but I think it's a little harsh what you're saying.

In each and every forecast they produce they outline the risk is very marginal and there's as much as a chance that nothing materialises.

So whilst their forecasts have been so called "iffy" lately, surely their recent forecast outlines their confidence for issuing such a high risk level.

[Flash bang flash bang etc]

1 minute ago, Ben Sainsbury said:

You aren't wrong, but I think it's a little harsh what you're saying.

In each and every forecast they produce they outline the risk is very marginal and there's as much as a chance that nothing materialises.

So whilst their forecasts have been so called "iffy" lately, surely their recent forecast outlines their confidence for issuing such a high risk level.

Probably my wording sorry, point simply being that CW haven’t ‘got it right’ in terms of where the storms actually occurred the last few times.

I don’t know what ‘getting the storm risk right’ means... surely a forecast is just a forecast?

Evidence is good that tomo will have some activity somewhere, but they keep chopping and changing our area so I’m waiting until tomorrow morning to decide whether to head out during the day and chase. Would be amazing to see two storms in one day if the evening risk comes off in the SE

[Ben Sainsbury]

8 minutes ago, Flash bang flash bang etc said:

Probably my wording sorry, point simply being that CW haven’t ‘got it right’ in terms of where the storms actually occurred the last few times.

I don’t know what ‘getting the storm risk right’ means... surely a forecast is just a forecast?

Evidence is good that tomo will have some activity somewhere, but they keep chopping and changing our area so I’m waiting until tomorrow morning to decide whether to head out during the day and chase. Would be amazing to see two storms in one day if the evening risk comes off in the SE

I completely understand apologies if I was also harsh! It's difficult to explain, when the conditions are marginal a forecast will always be issued than not. Therefore times like this more times than not the forecast will be wrong, so I agree with you there.

Anyhow I like that a lot of forecasts have been produced by a large variety of forecasters this time, provides me with greater confidence. And as a matter of fact to me it seems like an eternity since Nick have issued a "Yellow Thunderstorm Area" so I'm hopeful!

Edited April 20, 2018 by Ben Sainsbury

[staplehurst]

3 minutes ago, Flash bang flash bang etc said:

Probably my wording sorry, point simply being that CW haven’t ‘got it right’ in terms of where the storms actually occurred the last few times.

I don’t know what ‘getting the storm risk right’ means... surely a forecast is just a forecast?

Evidence is good that tomo will have some activity somewhere, but they keep chopping and changing our area so I’m waiting until tomorrow morning to decide whether to head out during the day and chase. Would be amazing to see two storms in one day if the evening risk comes off in the SE

Worth noting that up until now, no MDT risks have been issued - and hence all forecasts so far have suggested storms are more likely to not happen than to happen (SLGT = 30-45% chance). There are very few forecasts issued in this country that carry high confidence, and the greatest uncertainties are often mentioned in each forecast text.

We make mistakes, we're human - the point is to always verify your forecast to see if it went to plan or not, and if not try and find out what went wrong to ultimately avoid that mistake in the future. Two examples from the past month or so (15th March vs 3rd April) where the forecast didn't quite go to plan on one, but succeeded quite well on the other. (Black dots are the detected lightning strikes during each forecast period). In the case of the former, a post-event analysis was posted explaining what went wrong >> .

[Flash bang flash bang etc]

Just now, Ben Sainsbury said:

I completely understand apologies if I was also harsh! It's difficult to explain, when the conditions are marginal a forecast will always be issued than not. Therefore times like this more times than not the forecast will be wrong, so I agree with you there.

Anyhow I like that a lot of forecasts have been produced by a large variety of forecasters this time, brings me better confidence. And as a matter of fact to me it seems like an eternity since Nick have issued a "Yellow Thunderstorm Area" so I'm hopeful!

 

 

Ha! Yes I do love to see those yellows ?

So from what i understand so far the risk tomo early morning starts in the channel and moves up the west side of the U.K. and across the midlands into the afternoon where diurnals pep these up into fairly hefty storms, then we have a new round from about 8pm in the more central areas of the channel (south of IOW) moving in a similar track but taking these up over Hants, Surrey, the ‘Sexes and the ‘Folks.

Kent will get some action late evening and London will get some activity just after midnight.

(Don’t hold me to this tho!)