New CB developments off Cherbourg and that thunderstorm warning

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xmetman

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Jul 23, 2019, 5:28:59 PM7/23/19
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I wonder if this new CB development off Cherbourg (2100 UTC) will develop and affect the London area later tonight?

It did look an odd decision to exclude the whole of the SE from tonight's thunderstorm warning, I don't think anyone would have noticed if they hadn't, but because they did it drew my attention.

We'll just after see if those CB's keep on developing, there's plenty of SFERIC activity from it and virtually nothing from the area over the SW of England.


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robk fw190

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Jul 23, 2019, 5:54:40 PM7/23/19
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Seems to be a lot more Easterly track than suggested but looking now storms exploding in the SW as well.

Julian Mayes

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Jul 23, 2019, 6:09:55 PM7/23/19
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Developing now quickly into a mass outbreak from Wales, south Devon and soon into Sussex, then London - bound?   It is too warm to sleep right now so it'll be a late night looking out of the window and online. Lightning might be vivid too in the absence of moonlight.  

The mid-channel storms were a good test for the 1030 weather forecasters. The BBC London forecast did highlight the risk of storms for the London area - and fortunately they were on the graphic.  It does irritate me when forecasts do not take account of recent developments - the looking at the radar / satellite image / out of the window test. 

Julian   Molesey   

robk fw190

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Jul 23, 2019, 6:19:05 PM7/23/19
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Frequent vivid lightning visible over the Channel now from near Worthing.

xmetman

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Jul 24, 2019, 5:36:23 AM7/24/19
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I pushed out the original post at around 2215 BST last night.

It was based on a bit of speculation on my part and some trajectories from the last of the visible satellite images .

As you can see from the SFERIC map thunderstorms did affect London and the SE also the whole of East Anglia as well as the extreme NW which didn't feature in the original warning.


I was a bit late on it - then again I'm an armchair meteorologist who was on his way to bed after watching a bit of telly!

It took the Met Office almost another hour to update their thunderstorm warning that excluded the SE to include the SE.

This is another example of where a broad brush approach (at least 6") works best for warnings - or in technical terms - you might as well be hung for a sheep than a lamb.

I did manage to salvage a copy of the updated warning from my phone, they are very quick to dispose of any incriminating evidence from a previous warning (probably because it could be used in any litigation against them) and they don't maintain an archive.

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Dave C

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Jul 24, 2019, 7:58:41 AM7/24/19
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Stayed dry East of London.

xmetman

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Jul 24, 2019, 8:22:18 AM7/24/19
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There wasn't much rain east of London as you say, but it was a primarily a warning of thunderstorms and not heavy rain.

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Julian Mayes

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Jul 24, 2019, 9:39:02 AM7/24/19
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Here just SW of London I had just a trace - right on the eastern end of the main cen S Engl thunderstorm. Good C-C lightning though to west. 

I thought the radar did fairly well, i.e. not too much overestimation, though from watching the radar in real-time, I was surprised at only 0.8mm at Pembrey Sands. I often wonder about the t/bucket gauges just not recording smallish amounts of rain. 

If I may give a few extras to your map totals for 18-06h.....

Keele   21.0        Pennerley (Shropshire)   22.0     Morpeth Cockle Park   25.0    Winchcombe (Gloucs)   26.0     Cardiff Bute Park  27.0   - just east of your radar peak. The site is right in the geographical centre of the city.    Another cell over Suffolk gave 9.0 at Cavendish.  

Julian  


xmetman

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Jul 24, 2019, 11:04:00 AM7/24/19
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Yes, that rainfall estimate picked up the streak that ran north across south Wales quite well, but totals may have been a little high.
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