Convective Storm/Discussion thread - 16/07/16 onwards

[Roger J Smith]

Tomorrow, the potential appears marginal but I would expect one or two moderate thunderstorms along a decaying surface front becoming a trough oriented roughly along the M-1 corridor London to Coventry. Would expect one or two cells to achieve thunderstorm status mid-day, once formed these would tend to drift slowly north or even remain quasi-stationary so that heavy rain might be the biggest risk with them. Luton-Bedford area most at risk. Isolated heavy showers or weak thunderstorms elsewhere based largely on regional convergence or uplift. Nothing too major. Upper dynamics are weak, although marginally favourable. 

[Allseasons-Si]

Here is my three clips of the Stoke storm from yesterday,you'd be mistaken to think it was a storm because it didn't look like one,the third clip was almost constant thunder,enjoy

[Jason H]

7 hours ago, Ed Stone said:

It was truly immense, NS... Maybe the biggest anvil I have ever seen.

Here's a view of the East Anglia storm from yesterday evening taken from Dartford. Believe me, the overshooting top was massive!

 

 

[Nouska]

25 minutes ago, staplehurst said:

Frustratingly there are very few 12z soundings available for the UK, but if we take the Larkhill ascent from this afternoon and adjust the surface temperature to 25C with a dewpoint of 12C (which seems reasonable for the London area this afternoon etc), you can see that there is some convective potential, but it becomes capped off around 750mb (or approx 2.5km above the ground) due to warmer layers above - in fact it becomes even more capped off at 700mb (3km up), thus severely limiting the potential depth of convection.

Farther north, I suspect this capping in the mid-levels is slightly weaker, allowing parcels to achieve greater heights, but still capped off to a certain extent and hence the presence of some heavy showers over Merseyside recently, but with next to no lightning - it's not totally out of the question, but it's quite a low potential today.

You can get projected soundings for different parts of the UK on Meteociel - just look for the sondages from GFS, WRF, AROME or ARPEGE. ARP gives UK wide view for clicking on location.

http://www.meteociel.fr/modeles/sondage_arpege.php?region=uk&ech=3&mode=2&wrf=0

Choose petit emagramme to give a clearer view.

12Z run sounding for London.

Edited July 21, 2016 by Nouska

[staplehurst]

8 minutes ago, Nouska said:

You can get projected soundings for different parts of the UK on Meteociel - just look for the sondages from GFS, WRF, AROME or ARPEGE. ARP gives UK wide view for clicking on location.

http://www.meteociel.fr/modeles/sondage_arpege.php?region=uk&ech=3&mode=2&wrf=0

Choose petit emagramme to give a clearer view.

12Z run sounding for London.

Thanks - a useful site to have. Although forecast soundings will be limited by how many vertical levels are available in each model, but nonetheless are a useful tool - and in this case, plotting a projected Normand's Construction would also suggest any rising parcel would reach the capping inversion at approx 775mb.

[Greeny]

Its a bit later than what I wanted to post but this is the radar of the storms that split in two, as we know the south cell being the most potent..

At roughly 7pm and this was posted by a member that Norwich was about to get slammed and I had looked at the radar to see a potent core heading straight for us. I did something else whilst waiting for the storm to arrive hearing distant rumbles occasionally for about 10 minutes or so. I was thinking why it hadn't got louder and more frequent etc and when I looked at the radar, ouch! It split and the centre just flattened right out. Totally unexpected when it was that close. Crazy how it did that. Earler at around 6pm though I took these 2 pictures near Norwich Airport as it approached and it looked like it was moving quickly..

The credit is not mine for the rest of the pictures as they are from members of my FB group but here are some of them that I have chosen to share. I love this first one, the back end of the storm near Loddon..

Decent sized hail in Ashbocking Suffolk..

Cb from Cambridgeshire..

From Rendlesham..

Ormesby..

From Lowestoft..

and finally a roll cloud picture from Trimley St. Mary..

Ok so I missed out but I'm thankful for all of those who took pictures and video to show us what it was like from different areas. Thanks guys

 

 

Edited July 21, 2016 by Greeny

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Fri 22 Jul 2016 - 05:59 UTC Sat 23 Jul 2016

ISSUED 04:37 UTC Fri 22 Jul 2016

ISSUED BY: Dan

Atlantic upper trough continues to track eastwards on Friday, while sharpening and narrowing. The associated cool mid/upper levels atop a relatively warm/moist surface airmass, with dewpoints of 15-17C, will steepen lapse rates and generate a couple hundred Jkg-1 MLCAPE in response to diurnal heating. Expect scattered showers and a few weakly-electrified thunderstorms to develop in rather slack conditions, particularly focussed along zones of low-level wind convergence.

A couple of Low-end SLGTs have been issued where zones of convergence seem most likely to occur - although instability is rather limited and it is quite plausible that several heavy showers may not actually produce much in the way of lightning. Nonetheless, given PWAT of 30-35mm and rather slow storm motion, there is the risk of some local surface water flooding from prolonged heavy downpours and locally high rainfall totals. A few brief funnel clouds will also be possible.

http://www.convectiveweather.co.uk/forecast.php?date=2016-07-22

[Windblade]

16 hours ago, BrickFielder said:

So the Forecast SkewT has two main lines on it. The left one is the dew point  (The temperature at which moisture turns into water)  with height and the right one the temperature with height. So you look at the dewpoint at the surface and then work out at what height a rising parcel of air turns to water (I have marked that in purple). You then look at the adiabatic rate the green lines and work out when a parcel of air stops rising (thats the thick green line I have added).

The other chart is the humidity (moisture content of the air) at 300hPA (which would be thunderstorm top height). This tells me that there is drier air aloft where the blue is on the chart. Drier air usually means colder air which would shift the right hand line on the skewt leftwards meaning air parcels can rise higher where there is cold dry air aloft.

Thanks for explaining. That's what I love about this place - always new stuff to learn. I'm still a bit confused how you work out what height a parcel of air turns to water (is there a set temperature range this occurs in for example?) and how do you work out when the air stops rising?

[Windblade]

14 hours ago, Greeny said:

 

That third picture is beautiful (the sunset one). That storm looks like a real beast.

Edited July 22, 2016 by Supacell
No need to re-quote entire post

[Windblade]

So today its raining (at last) in my area. Lovely, lovely cool rain! I also see on convectiveweather.co.uk a chance of storms. I'm not going to get too excited as that would be too good to be true at the moment but at least its a little cooler. Currently 18.5 degrees.

 

Edited July 22, 2016 by Windblade

[Gael_Force]

10 minutes ago, Windblade said:

That third picture is beautiful (the sunset one). That storm looks like a real beast.

The pictures are great but please just quote a wee bit of the post.

[Gordon Webb]

well looking at GFS storm risk chart it goes no higher than 30% or 40% chance and convectiveweather.co.uk forecast is not sparkling for those that want storms however the reason I'm posting is that when I look at the GFS storm risk charts look I did the other day they had 60% chance is some areas in the color Green some in Yellow and only a 10% chance in France but that was Red , Is this a indicator of Intensity or something else ?

Edited July 22, 2016 by Gordon Webb

[Harry]

It is very humid in London today, perhaps the most humid 'feeling' it has been for several weeks (including the heatwave earlier this week).

Leads me to suggest that while any showers today may not be incredibly electrical, downpours could be very intense.

[Gordon Webb]

met office have issued warnings for W and E midlands E England and London and SE England of course the majority of the W Midlands is in the clear so for those who have plans I wouldn't worry too much

 

Edited July 22, 2016 by Gordon Webb

[Gordon Webb]

10 minutes ago, Harry said:

It is very humid in London today, perhaps the most humid 'feeling' it has been for several weeks (including the heatwave earlier this week).

Leads me to suggest that while any showers today may not be incredibly electrical, downpours could be very intense.

that seems to be the consensus looking at all forecasts slow movement and the amount of rain deposited might be the main concern today

[Windblade]

1 hour ago, Gael_Force said:

The pictures are great but please just quote a wee bit of the post.

What was wrong with showing the whole post mate? To be honest I just hit the quote button and let it do the work! Besides, I wanted to show the pictures.

Edit - Just to clarify I wasn't being funny or anything so please don't take what I said the wrong way, just wanted to know why you had an issue with my quote?

Edited July 22, 2016 by Windblade

[Summer Sun]

Issued at:0901 on Fri 22 Jul 2016

Valid from:1110 on Fri 22 Jul 2016

Valid to:2200 on Fri 22 Jul 2016

Heavy showers and thunderstorms will break out during the late morning and afternoon before slowly fading this evening. Whilst some places will miss the heaviest showers, where showers do occur they are likely to be prolonged allowing some large amounts of rain to fall. Please be aware of the potential for localised flooding and disruption to travel.

Chief Forecaster's assessment

Heavy showers and thunderstorms are expected to break out later this morning and this afternoon before slowly fading this evening. Due to light winds, some of these showers will be slow-moving leading to some localised and prolonged, torrential thundery downpours which could give 20-25 mm of rain in a relatively short space of time and very locally in excess of 50 mm in two or three hours. The heaviest showers are likely during the afternoon and early evening, so are likely to coincide with the rush hour. As is often the case in sort of situation, some places will miss the showers whilst nearby locations experience heavy downpours. Meanwhile, the exact location of where the very heaviest showers occur is very uncertain but perhaps slightly more likely over western parts of the warning area.

Covers

Warwickshire

Leicester, Leicestershire, Lincolnshire, Northamptonshire, Nottingham, Nottinghamshire, Rutland

Bedford, Cambridgeshire, Central Bedfordshire, Hertfordshire, Luton, Peterborough

Bracknell Forest, Buckinghamshire, Greater London, Hampshire, Milton Keynes, Oxfordshire, Reading, Slough, Surrey, West Berkshire, West Sussex, Windsor and Maidenhead, Wokingham

http://www.metoffice.gov.uk/public/weather/warnings/#?WT.mc_id=Twitter_Warnings_Rain&tab=map&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1469142000&regionName=se

[Windblade]

1 minute ago, Summer Sun said:

Issued at:0901 on Fri 22 Jul 2016

Valid from:1110 on Fri 22 Jul 2016

Valid to:2200 on Fri 22 Jul 2016

Heavy showers and thunderstorms will break out during the late morning and afternoon before slowly fading this evening. Whilst some places will miss the heaviest showers, where showers do occur they are likely to be prolonged allowing some large amounts of rain to fall. Please be aware of the potential for localised flooding and disruption to travel.

Chief Forecaster's assessment

Heavy showers and thunderstorms are expected to break out later this morning and this afternoon before slowly fading this evening. Due to light winds, some of these showers will be slow-moving leading to some localised and prolonged, torrential thundery downpours which could give 20-25 mm of rain in a relatively short space of time and very locally in excess of 50 mm in two or three hours. The heaviest showers are likely during the afternoon and early evening, so are likely to coincide with the rush hour. As is often the case in sort of situation, some places will miss the showers whilst nearby locations experience heavy downpours. Meanwhile, the exact location of where the very heaviest showers occur is very uncertain but perhaps slightly more likely over western parts of the warning area.

Covers

Warwickshire

Leicester, Leicestershire, Lincolnshire, Northamptonshire, Nottingham, Nottinghamshire, Rutland

Bedford, Cambridgeshire, Central Bedfordshire, Hertfordshire, Luton, Peterborough

Bracknell Forest, Buckinghamshire, Greater London, Hampshire, Milton Keynes, Oxfordshire, Reading, Slough, Surrey, West Berkshire, West Sussex, Windsor and Maidenhead, Wokingham

http://www.metoffice.gov.uk/public/weather/warnings/#?WT.mc_id=Twitter_Warnings_Rain&tab=map&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1469142000&regionName=se

Thats more like it!

[Joseph Hudson]

feel a lot warmer today and very sunny but with some menacing looking clouds 

[sparky1972]

morning all, was surprised to see a weather warning for my area today, certainly not feeling remotely humid or thundery at the momment, feeling very fresh after this morning early rain/drizzle

[Windblade]

Yes, the rain here has really helped it feel much fresher. It was a welcome relief to the horrible sticky heat we've been having. To be honest I hope we get some more, even if its not thundery/stormy, its just nice to cool the air down.

[sparky1972]

 a few pics of the storm as it hit here wednesday evening.

[Nick F]

Storm & Convective Forecast

Issued 2016-07-22 09:16:18

Valid: 22/06/2016 0600z to 23/06/2016 0600z

CONVECTIVE/STORM FORECAST - FRI 22ND-JULY-2016

Synopsis

An upper trough will slide east across the UK and western Europe as an extension of upper low complex over the far North Atlantic, a slack but moist surface airmass across the UK will become unstable to surface heating this afternoon ahead of an occluded front moving across the west today, with heavy showers and thunderstorms developing in places.

... ENGLAND, WALES and ERN SCOTLAND ...

The slack/weak surface flow across much of the UK will feature several convergence zones across the above areas, which will tend to strengthen as the day goes on due to surface heating inland creating strengthening sea breezes to spread inland. A moist airmass, (characterised by dew points of 15-17C) and surface heating into the low to mid 20s deg C will generate around 300-600 j/kg CAPE. Lapse rates don't look particularly steep on GFS progs, which will prevent greater instability generally, so thunderstorms will tend to be confined to convergenze zones where strongest updrafts will establish.

Given high moisture content of the atmosphere across the above areas (PWAT values of 27-30mm) and weak upper winds, slow-moving torrential downpours leading to localised flash-flooding will be the main threat from any storms. Have issued a MARGINAL risk for flooding for SW England, parts of central S and SE England, E Midlands and parts of E England - as strongest convergence/storms seem most likely here this afternoon.

Any hail will tend to be isolated and small given modest CAPE, weak winds aloft and surface convergence will favour the development of a few funnel clouds.

Issued by: Nick Finnis

[Windblade]

Thanks Nick. That's looking much better! Its stopped raining in London (in tower hamlets area today) but we do have some lovely dark skies to the north...

Edited July 22, 2016 by Windblade

[MattTarrant]

Excellent weather here this morning, supplying plenty of surface heating with temperatures already rising nicely!! Could do with a few thunderstorms as have missed the majority of them this year. Wind convergence looks most likely to help storms here because CAPE is relatively low, wind is almost non existent so storms could cause some local flash flooding.