Storm & Convective Discussion - 1 September 2015 onwards

[Supacell]

Sleaford making its mark with a tornado 'Yet Again'!! 

 

Lincolnshire is storm county, no doubt about it.

[Hodgheg]

Anyone have radar grabs from the storms that produced todays tornadoes and would they have been classed as low topped supercell tornadoes or more likely to be land spouts? Todays storms seemed much more organised than forecast, would that be correct and if so why?

[Greeny]

Anyone have radar grabs from the storms that produced todays tornadoes and would they have been classed as low topped supercell tornadoes or more likely to be land spouts? Todays storms seemed much more organised than forecast, would that be correct and if so why?

 

The most intense storms I believe were given an extra boost by wind convergence as predicted by the NMM. The run I saw a couple of days ago had the convergence being like a head on collision, later runs had the convergence like a catherine wheel, although shear was weak today this wind convergence helped to get rotation in storms. I'm not sure if any storms however weak they are that rotate are classified as supercells. A supercell is classified as a storm with the presence of a mesocyclone. I have seen smaller storms rotate and right move on radar but they are not that intense, I'm not sure if they are classed as supercells though. I don't know if anyone can clarify this.

[Muffelchen]

We had a spell of thunder and lightning here in the last hour. The main area of heavy rain was just to the east but we still had a good show and around 5mm from it.

 

There's now been more thunder here in the last few days than all of summer put together!

Died just as it got here Reef and saw and heard nowt. Glad you got something from a southeasterly on a murky evening: many is the time you have moaned how the N Sea cold kills storms! Generally true in my experience but this time not: I think the darkness coming on did the job here.

[Flash bang flash bang etc]

Interesting read from Tony Gilbert over at UKWW about a rather surprising overnight tornado risk for southern counties later on tonight.

I won't pretend to understand the science but this guy is one of the people to listen to when it comes to all things convective in the UK, so will be interesting to see what happens.

Also, to all those in the region he marked out as a risk zone - a tornado may well be unlikely but any strong wind can cause damage and disruption, so be careful out there :-)

Edited September 14, 2015 by Flash bang flash bang etc

[Greeny]

It is a bit easier to see on the 500 metre radar but from about 14.20 a cell develops and seems to right move over Northampton. I'm not sure what time the tornado was seen and recorded so don't know if it coincides with the time of the tornado.

[Daniel*]

Yea I got me some of this too. Great value!

Maybe yours burst open in transit. The packaging isn't that great TBH

I approve

[Nick F]

After what turned out a rather interesting day for central and eastern England, with some credible reports and images of separate tornadoes on the ground, we may squeeze in a few more storms on Tuesday, particularly over southern and eastern England - where lapse rates look steepest, also low LCLs and wind convergence may setup the ideal condiitons for tornadoes again.

 

Netweather's Storm forecast for Tuesday: http://www.netweather.tv/index.cgi?action=convective;sess=

[Gordon Webb]

don't seem to be in the real trouble spot today which is good as have shopping to do

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For tomorrow with the ex torpical storm coming in, surely the above could lead to a squall line of some sorts??

[Summer Sun]

Yellow warning issued by the met office

 

Issued at: 1058 on Tue 15 Sep 2015

Valid from: 0800 on Wed 16 Sep 2015

Valid to: 0900 on Thu 17 Sep 2015

 

Persistent and at times heavy rain is expected to spread from south to north during Wednesday, this affecting much of England and Wales. Some heavy and thundery showers could also develop across East Anglia and southeast England during the afternoon. Strong and gusty winds are also expected, with gales in exposure. Rain should ease from the southwest later on Wednesday, but will persist across the north of the warning area into Thursday. Some localised flooding is possible from fast responding water courses and standing water, this perhaps disrupting travel. Lightning associated with the afternoon showers across East Anglia and SE England will be an additional hazard.

 

Chief Forecaster's assessment

 

A complex area of low pressure is expected to deepen over the Bay of Biscay later today and into Wednesday, before pushing north towards the UK. Rain will arrive into southern areas Wednesday morning, before spreading to the rest of the warning area through Wednesday afternoon and into Thursday. Rain should ease from the south during the day, though some heavy and thundery showers may develop across the southeast and East Anglia through the afternoon and evening. Most parts of the warning area should see 15-30 mm of rain, however some places could see as much as 40-70 mm. Furthermore, thunderstorms developing across the southeast and East Anglia Wednesday afternoon have the potential to generate 15-25 mm of rain in a few hours. This is a very complex development, and uncertainty in timings and areas most at risk is large. As such this warning will be updated as confidence in developments increases.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1442358000&regionName=uk

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Some convection kicking of here.. Nothing special though

[Flash bang flash bang etc]

I would say it's been a bit of a squib so far today. Not even rogue thundery showers.

That'll teach people to forecast storms for a part of the UK that doesn't 'do' storms

[NO LONGER POSTING]

I would say it's been a bit of a squib so far today. Not even rogue thundery showers.

That'll teach people to forecast storms for a part of the UK that doesn't 'do' storms

 

You spoke to soon.. is was always a "risk" today anyway still time for something though 

[Flash bang flash bang etc]

You spoke to soon.. is was always a "risk" today anyway still time for something though

Yes an amazing storm right over London! ;-P

[NO LONGER POSTING]

Yes an amazing storm right over London! ;-P

 

I think tomorrow will bring some "fun and games" to the south.. 

[Winter Cold]

Im probably just imagining this but ive just watched a very strange cloud go past which seemed to be rippling and developing circles within the cloud structure. It also seemed to be dropping slightly from the middle. Could I have seen a little bit of rotation here and the early stages of something??

 

Ive tried to get some pics, best 2 are here:

 

  

[Flash bang flash bang etc]

Im probably just imagining this but ive just watched a very strange cloud go past which seemed to be rippling and developing circles within the cloud structure. It also seemed to be dropping slightly from the middle. Could I have seen a little bit of rotation here and the early stages of something??

 

Ive tried to get some pics, best 2 are here:

 

IMG_20150915_144515.jpg   IMG_20150915_144455.jpg

Doesn't look dark / dense enough to me but I am aware photos don't always capture the 'darkness' of storms properly. Certaintly looks quite unusual though...

[Andy Bown]

Im probably just imagining this but ive just watched a very strange cloud go past which seemed to be rippling and developing circles within the cloud structure. It also seemed to be dropping slightly from the middle. Could I have seen a little bit of rotation here and the early stages of something??

 

Ive tried to get some pics, best 2 are here:

 

IMG_20150915_144515.jpg   IMG_20150915_144455.jpg

There's always a chance that clouds could contain movement in addition to the general direction they are moving. Clouds by their very nature are always changing shape/form. You could have local convergence (winds from different directions meeting each other) which will add to different movements.

 

An example from here this afternoon (no pics) is that I was putting washing on the line and noticed an anvil moving overhead attached to a dark based shower cloud which the Net Weather radar showed as moving just North of my location. Over the next 15 mins the anvil (moving SE) detached from the dark base and produced a drizzly sprinkle while the actual shower cloud (moving NE) dissipated from a Towering Cumulus to broken Altocumulus.

 

An aside from the above, a long convergence line of showers has developed in the last 90 minutes stretching from Cornwall to South of London!

[Winter Cold]

Cheers guys   was fun to watch anyway!

 

Lets see what fun and games tomorrow might bring

[Rain123]

Right - any thoughts on tomorrow anyone? An MCS?

[Allseasons-Si]

Right - any thoughts on tomorrow anyone? An MCS?

 

 

Micro convective shower

[Rain123]

Micro convective shower

Good one! Looking at BBC graphics, looks like an area of rain with embedded thunderstorms tomorrow afternoon/evening. There is some decent CAPE to back that up and a storm risk of up to 50%, at around 1300-1800. Temperature is a bit of a dissapointment though, so I wouldn't expect a July-style plume. I would say anywhere eastwards from the isle of wight, and southwards from the wash are in with a chance tomorrow afternoon.

 

Thats my first go at a proper sypnosis, so would take that with a sprinkling of salt. Hopefully some of the more experienced forecasters will be able to do it much more accurately and in-depth.

Edited September 15, 2015 by Rain123

[Supacell]

It is a complicated one but I will attempt an amateur go at what I think will happen.

 

There seems a quite good risk of thunderstorms developing in the afternoon and evening under the influence a low pressure system with tropical storm origins (Henri). 

 

Current charts are still at this late stage subject to change as the low moving up from the south may not take the exact track which is currently predicted. There is also still some disparagy between models. However, it would appear that the best chance is south-east of a line from about The Wash to Dorset, behind a band of heavy rain which itself could produce disruptive weather. The strongest CAPE occurs in between about 12noon and 4pm around southern coastal regions along with the far SE and East Anglia. Basically it looks like the further south-east you are the better.

 

There is a lot of moisture caught up with this system and so any thunderstorms that do develop could produce a lot of water in a short space of time. There is also around 20-30knts of deep layer shear available which could help to organise storms that do form. Helicity in the southeast will promote a risk of supercells and a possible tornado risk also. Lightning and hail is also a risk despite lapse rates not being that impressive to my eye. Winds gusting over 50mph generally, not necessarily only attributed to convection.

 

Outside of the risk of thunderstorms there is the risk of widespread very heavy rainfall and gale force gusts of wind and so a risk of flooding and wind damage for most of England, Wales and SE Scotland. NW Scotland and N Ireland look to escape it entirely.

 

A slight change in track could completely change this forecast with the thundery weather remaining on the continent if the track is further east/south or affecting more of us if the track is further west/north.

Edited September 15, 2015 by Supacell

[Singularity]

The models seem to be struggling to capture the deep convection associated with the system - many of the higher resolution ones seem to have little precipitation associated with it until it reaches The Channel, which is a bit odd but may be related to issues with data assimilation at the beginning.

 

Anyway, France's very high resolution AROME model develops quite a lot of downpours within the leading area of general heavy rain:

 

 

...but the positioning is further west than most models have it. If the low tracked that far west, the southeast would be at risk of seeing some of the stronger wind gusts on the eastern side (up to nearly 50 mph perhaps).

 

There's then a fairly small region in which heavy showers and possible thunderstorms develop across S'rn England (see below), which advances quickly NE.

 

 

 

This is just one of a remarkably wide variety of options being put forward by the models tonight, with most taking the low and areas of rain a bit further east, some keeping the leading area of rain further south, and projected rainfall totals between 6am and 6pm that on the local scale range from less than 10 mm to around 70 mm, depending on the exact distribution of those downpours.

 

So there will probably be a fair few on here who see a 'damp squib' event, while others experience a day to remember.