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Convective/Storm Discussion Thread - 1st August onwards


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3 hours ago, Weather-history said:

Woken by loud thunderclap at about 12.20am. Not sure why the thunder was so loud and seemed to be drawn out.

https://mobile.twitter.com/AlanRenza/status/897978616579010564/video/1

 Definitely a +CG, And less than a mile as well. Had a few of them around here in the last few years.  Can be a sign of a decaying cell. I've heard it hypothesised that pollution from large cities can increase their probability. 

Edited by Chris.R
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My contribution to this evening.

What a fantastic night we had in central southern England, and many other places too! I've never seen storms of that intensity or frequency in April before! Anyway I thought I would share so

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Manchester METAR had the cloud-base last night at 800ft, could be just amplification of the thunder carrying it further? Although the lightning was a little strange here in that it wasn't visible in the usual type where you can see the trail, it was more the quick-bright flash type of lightning.

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Just now, SNOW_JOKE said:

Manchester METAR had the cloud-base last night at 800ft, could be just amplification of the thunder carrying it further? Although the lightning was a little strange here in that it wasn't visible in the usual type where you can see the trail, it was more the quick-bright flash type of lightning.

Yeah, I saw no bolts, just flashes.  Is 800ft high or low for a cloud base?  At the time, to me, it felt as if the storm was elevated

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Went to bed at 11pm last night and slept through it:nonono:,could be that i had one too many lol

it is quiet warm out there today too

anyways,the WRF 2km is pretty spot on at the moment from it's 06z hrs at 15:00 hrs with the ppn just to my NW.

nmm_uk1-1-7-0.png?17-12

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7 minutes ago, SNOW_JOKE said:

Manchester METAR had the cloud-base last night at 800ft, could be just amplification of the thunder carrying it further? Although the lightning was a little strange here in that it wasn't visible in the usual type where you can see the trail, it was more the quick-bright flash type of lightning.

Noticed the low cloud base last night almost felt indoors out ,sporadic lightning and loud booming thunder around 1.30 -2.30 this morning .

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I'm 690ft in elevation but I couldn't quite tell what the actual cloud-base was due to the rain, just to throw into the mix was the added moisture from the goyt forest that was being 'pulled' upwards and was pooling into the valley. But the cloud-base was definitely hugging the tops of the hills here as there's a few farms near to the summits and their floodlights had gone from view.

The lightning seemed to come in pulses as initially I saw it coming from the west towards Macclesfield direction and it quietened down for around 10 minutes, then the lightning began flickering locally every few minutes for around 35mins. Not the type of storm where you're expecting a bolt to come every couple of seconds, but where you're anticipating the next place it's going to come from after 2 or 3 minutes of waiting.

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there's a nice stream of developing heavy showers heading straight for me (20 miles to the SW) which have matured in the past 30 mins or so.....It'll be interesting to see if they become electrified shortly!

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7 minutes ago, ajpoolshark said:

there's a nice stream of developing heavy showers heading straight for me (20 miles to the SW) which have matured in the past 30 mins or so.....It'll be interesting to see if they become electrified shortly!

Indeed, very dark just to my south, but can't see much structure to the cloud due to a lot of lower cloud being blown by in front of it. Could be some intense downpours locally soon.

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sure we had a positive strike not far from here last night,  maybe two or three miles , but the deep low frequency explosive sound reverberated into the distance for ages

I missed rather spectacular funnel cloud last week over Wigan that touched down in fields in Billinge area   

 

http://www.manchestereveningnews.co.uk/news/greater-manchester-news/incredible-footage-captures-swirling-twister-13466112

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Day 2 Convective Outlook

VALID 06:00 UTC Fri 18 Aug 2017 - 05:59 UTC Sat 19 Aug 2017

ISSUED 22:35 UTC Thu 17 Aug 2017

ISSUED BY: Dan

Broad longwave trough will swing eastwards across the British Isles on Friday, accompanied by notably steep lapse rates. Scattered showers and thunderstorms will form fairly widely given widespread deep instability, with areas of longer spells of rain associated with organised frontal features also.

Hard to be more specific at areas with the best potential, though a favourable overlap of instability and shear will exist across S Wales - S Midlands / Cen S Eng - East Anglia / SE England which would suggest this region at a higher risk of lightning activity than environs. Perhaps another focus over Yorks/Lincs where steepest lapse rates will exist by the afternoon. Quite dry forecast profiles suggest showers will be fairly well-scattered, though steering flow resulting with ultimately a fairly widespread coverage. Hail locally up to 2.0cm in diameter will be possible with the strongest cells, along with strong, gusty winds.
 
 
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Storm & Convective Forecast

convmap_180817.thumb.png.4895b133ff5ebfa1f3eb6c22f7c4a721.png

Issued 2017-08-18 07:38:15
Valid: 18/08/2017 6am to 19/08/2017 6am

Day 1 Convective / Storm Forecast

Synopsis

Upper trough crosses the UK during Friday, at the surface – parent low moves east to the N of Scotland while one or two surface troughs with associated occluded fronts on the southern side of the low cross the UK and Ireland. An unstable Wly veering NWly flow covers most of the UK, with a risk of thunderstorms developing with diurnal heating.

… IRELAND, N. IRELAND, ENGLAND, WALES and S SCOTLAND …

A wedge of rather steep lapse rates over Ireland and far west of UK this morning, associated with cold pool of mid-level air in axis of upper trough moving east, will support the development eastwards of heavy showers / thunderstorms across much of the above areas through the rest of the morning and through the afternoon … as diurnal heating increases surface instability … with GFS indicating 300-700 j/kg across large parts of the UK during peak heating this afternoon away from north Scotland … where cloudier skies and dynamic rainfall will be prevalent.

Deep layer shear will be fairly weak generally, which will mean showers/storms will be disorganised and pulse-type on the whole. However, across S Ireland, S Wales and S England – stronger Wly flow aloft and 30knts+ of DL shear may organise showers/storms better into clusters/line segments capable of producing marginal risk of strong wind gusts (40-50mph), marginal risk of hail up to 2cm in diameter + marginal risk of flooding. Also, backing of winds / increase in low-level shear ahead of troughs moving through combined with local topographical effects on flow may enhance the risk of an isolated tornado too across S Ireland, Wales and SW England – where LCLs (Lifted Condensation Levels) or cloud bases will be lowest.

 

Issued by: Nick Finnis

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Huge downpour here this morning leaving 9mm in the rain gauge in less than 15 minutes. Probably would've been more if the rain wasn't sideways at times. Exciting start to the day.

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