Storm & Convective Discussion - 1 September 2015 onwards

[Spikecollie]

Carol Kirkwood made quite an issue out of the thunderstorms for the S/SE on BBC Breakfast this morning, but let's see what happens. Certainly look like it is beginning to start up in France already and the likes of Limoges and Cognac METARs are forecasting t-storms. I hope some of you get something - I'm heading down south tomorrow night to take the ferry to St.Malo, but it looks like I will miss anything interesting (which is probably not a bad thing!).

[Flash bang flash bang etc]

Didn't think we would get anything but let's see what's happening at 2pm. That's the time most of the forecasts I read predicted storms would start

[Greeny]

http://www.estofex.org/

estofex's thoughts on todays potential..

[Singularity]

Cells just exploded in the Chanel south of Weymouth - from trace amounts to over 16 mm per hour in the space of 15 minutes.

 

There's also a distinct arc of convection leaving N. France, hints of the kind of organisation that could produce some nasty wind gusts along with that tornado threat.

[staplehurst]

00z EURO4 vs the radar for the same time: 11:00 BST. Pretty good handling of things so far - model is never going to get placement of thunderstorms right (near Jersey) but it's areas of dynamic rain are in fairly good agreement...

 

So all in all, it appears to be going to plan. Heaviest rain always developing this afternoon as the approaching shortwave trough and increasing baroclinicity serve to intensify the front, while advecting the unstable moist air from the Continent across into CS/SE England then E Anglia (evident over Channel Islands at 11:00).

[Flash Elvis]

Cannot believe I have just read this!!!

 

http://www.echo-news.co.uk/news/13720534.Updated__Weather_warning_as_heavy_rain_and_risk_of_tornadoes_predicted_for_Essex/

Edited September 16, 2015 by Flash Elvis

[NO LONGER POSTING]

Cannot believe I have just read this!!!

 

http://www.echo-news.co.uk/news/13720534.Updated__Weather_warning_as_heavy_rain_and_risk_of_tornadoes_predicted_for_Essex/

 

Oh dear god.. 

[Singularity]

The low cloud bases was something that really caught by eye when looking at the models yesterday evening. Between 50 and 200 m does look likely at times.

 

Any lightning activity may seem especially loud and with a high risk of them being cloud to ground rather than inter-cloud.

 

Precipitation wise, 70 mm is not an unreasonable expectation on a very localised scale. We're taking like 1 in 100 towns or something.

Edited September 16, 2015 by Singularity

[William Grimsley]

Well, I just had a nice walk in some of the biggest drops on earth, even the puddles were bubbling at one point and to make it even more weird, it was falling out of cirrus cloud! Some rapid development now to my SE, not expecting anything thundery at this stage.

[NO LONGER POSTING]

I say give it a couple of hours and things are going to go nutty 

[Flash Elvis]

If its been reported like that.... then I will be putting my shorts on and factor 50 cause we are getting a heatwave!!!

 

Will keep watching the radar as always and fingers crossed we will get a decent light show later this afternoon or early evening

[William Grimsley]

People in central southern England need to watch out, some really nice developments now starting to form up through the western side of the Cherbourg Peninsula heading towards the IOW.

[Winter Cold]

Seems to me then that the rain band idea is being abandoned and we're just looking for storm development in the SE, maybe!

 

I was expecting to see a big, bright intenese 'proper' band of rain pushing north by now according to the forecast but theres no such thing. Its definately changed and anyone who says today is going to plan is wrong in my opinion, based on expectations at just T12 ago anyway.

[William Grimsley]

Seems to me then that the rain band idea is being abandoned and we're just looking for storm development in the SE, maybe!

 

I was expecting to see a big, bright intenese 'proper' band of rain pushing north by now according to the forecast but theres no such thing. Its definately changed and anyone who says today is going to plan is wrong in my opinion, based on expectations at just T12 ago anyway.

Not sure if this is entirely true, developments are starting to rapidly form and there is a 'proper' band of rain now pushing into Devon and Dorset and moving NNW along with further heavier and thundery rain now pushing up from the Channel Islands towards Dorset and Hampshire.

Edited September 16, 2015 by William Grimsley

[Winter Cold]

Not sure this entirely true, developments are starting to rapidly form and there is a 'proper' band of rain now pushing into Devon and Dorset and moving NNW along with further heavier and thundery rain now pushing up from the Channel Islands towards Dorset and Hampshire.

 

Yes things are developing down south but from the way it was being said yesterday it was supposed to be a big broad intense band pushing well north by now and giving flooding risk and difficult driving conditions etc, maybe with embedded storms and then main storm risk behind it in SE.

 

Maybe the front is developing in situ but the way I understood it i was expecting to see the bright colours on the radar starting to appear out of France early this morning and then it should have been well up into England by now.

Im not having a go or anything, as I said the weather can make fools of us all, and I understand its a complex situation but in my opinion today is very different to what the TV said even at 10pm last night for example.

[staplehurst]

Yes things are developing down south but from the way it was being said yesterday it was supposed to be a big broad intense band pushing well north by now and giving flooding risk and difficult driving conditions etc, maybe with embedded storms and then main storm risk behind it in SE.

 

Maybe the front is developing in situ but the way I understood it i was expecting to see the bright colours on the radar starting to appear out of France early this morning and then it should have been well up into England by now.

Im not having a go or anything, as I said the weather can make fools of us all, and I understand its a complex situation but in my opinion today is very different to what the TV said even at 10pm last night for example.

That's why a forecast from last night (i.e. 12-18 hours out) should never be taken as gospel in such an uncertain period of weather - and if referring to the BBC forecasts, that is essentially one model run that has been modified by the Met Office to reflect the current thoughts at the time that model was issued (bearing in mind, the BBC graphics at 10pm are based on the 06z EURO4, ie the raw model data is a good 16 hours old, with subsequent tweaks by the MetO and BBC respectively). Some model guidance yesterday suggested most places would remain dry until the afternoon - as seems to be the case. The overall message yesterday was for light and patchy rain to spread northwards, and intensify during the afternoon in-situ as the second shortwave trough approaches from the southwest. Yes there has been less patchy rain around this morning than perhaps hinted at yesterday, but that is the nature of an inexact science, especially in such a complex situation where it is likely to continue to change.

Edited September 16, 2015 by staplehurst

[bobbydog]

Chief Forecaster's assessment

A complex area of low pressure over the Bay of Biscay and NW France Wednesday morning is expected to track northeast, crossing SE England as it does so, to become located over the North Sea by, or soon after, midnight. Rain will arrive into southern areas Wednesday morning, before slowly spreading to the rest of the warning area through Wednesday afternoon and night. The more persistent rain should ease across the SE this afternoon, but is expected to be replaced by some heavy and thundery showers which will last into the evening. Most parts of the warning area should see 10-20 mm of rain, however some places could see as much as 30 to 50 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 remains a complex development, with some uncertainty in timings and areas most at risk. As such this warning may be updated as developments evolve.

seems fairly accurate to me...

[stainesbloke]

Yes things are developing down south but from the way it was being said yesterday it was supposed to be a big broad intense band pushing well north by now and giving flooding risk and difficult driving conditions etc, maybe with embedded storms and then main storm risk behind it in SE.

 

Maybe the front is developing in situ but the way I understood it i was expecting to see the bright colours on the radar starting to appear out of France early this morning and then it should have been well up into England by now.

Im not having a go or anything, as I said the weather can make fools of us all, and I understand its a complex situation but in my opinion today is very different to what the TV said even at 10pm last night for example.

Yes, I watched the BBC forecast late last night and today has turned out completely differently so far. Not to say there won't be thundery stuff kicking off later but the forecast initial rain band hasn't materialised as yet. We might just skip that and go straight to storms down here with any luck!

[Flash bang flash bang etc]

Cannot believe I have just read this!!!

 

http://www.echo-news.co.uk/news/13720534.Updated__Weather_warning_as_heavy_rain_and_risk_of_tornadoes_predicted_for_Essex/

Whoa - 70 million meters of rain!

[William Grimsley]

Yes things are developing down south but from the way it was being said yesterday it was supposed to be a big broad intense band pushing well north by now and giving flooding risk and difficult driving conditions etc, maybe with embedded storms and then main storm risk behind it in SE.

 

Maybe the front is developing in situ but the way I understood it i was expecting to see the bright colours on the radar starting to appear out of France early this morning and then it should have been well up into England by now.

Im not having a go or anything, as I said the weather can make fools of us all, and I understand its a complex situation but in my opinion today is very different to what the TV said even at 10pm last night for example.

You're definitely correct there. Maybe I was thinking differently, I tend to think of the worst scenario these days after my run ins with the accuracy of the BBC Weather forecasts which are now shambolic and not even worth looking at.

[Winter Cold]

That's why a forecast from last night (i.e. 12-18 hours out) should never be taken as gospel in such an uncertain period of weather - and if referring to the BBC forecasts, that is essentially one model run that has been modified by the Met Office to reflect the current thoughts at the time that model was issued (bearing in mind, the BBC graphics at 10pm are based on the 06z EURO4, ie the raw model data is a good 16 hours old, with subsequent tweaks by the MetO and BBC respectively). Some model guidance yesterday suggested most places would remain dry until the afternoon - as seems to be the case. The overall message yesterday was for light and patchy rain to spread northwards, and intensify during the afternoon in-situ as the second shortwave trough approaches from the southwest. Yes there has been less patchy rain around this morning than perhaps hinted at yesterday, but that is the nature of an inexact science, especially in such a complex situation where it is likely to continue to change.

 

Absolutely, its been a hard one to get right, as I say im not bashing anyone, just merely pointing out that today is looking to turn out very different as first thought. As you say today is a perfect example of how forecasts can go wrong, even at such short notice.

 

I must say though if thats the case with the TV forecasts im shocked that they use such old data, but thats for another topic lol

[William Grimsley]

Well, it looks like the rain band is getting it's act together, if slowly... Expecting some moderate/heavy rain shortly.

[legritter]

A very interesting day coming up ,its all now coming together and looks to me that things will quickly change so i,m going to check every hour or so on radar and still time for surprises as its all very complex ,well thats the nature of our hobby  very frustrating at times but that goes with a Science thats not exact even here in the year 2015 .

Television forecasts have always been open to big changes over the day not so much these days but generally its been a case of collecting Data and getting in on the screen in the form of a forecast ,time is limited to telly forecasts  but its great we now have the Web in our interest ,some action now as regards to thundery activity to our south ,best of luck to all 

[staplehurst]

I must say though if thats the case with the TV forecasts im shocked that they use such old data, but thats for another topic lol

 

Indeed - but I'll just leave with this thought: the newest model run is not necessarily the most accurate 

 

If you've edited a model run to be in-line with the best guess, and a new run comes in and you don't agree with it - why would you then roll out the new run? etc

[East_England_Stormchaser91]

Thundery activity had died a death in the channel. Even Paris is missing out with the nearest action to the south of there!

Unless something fires in the next 5 hours, what a bust this will be!