On Wednesday, July 26, 2017 at 6:36:51 PM UTC+1, Graham Easterling wrote:
On Wednesday, July 26, 2017 at 5:49:09 PM UTC+1, wrote:
On Thursday, July 20, 2017 at 2:56:57 PM UTC+1, Graham Easterling wrote:
On Thursday, July 20, 2017 at 2:54:39 PM UTC+1, Graham Easterling wrote:
SNIP
On Tuesday, July 18, 2017 at 7:11:57 PM UTC+1, Graham Easterling wrote:
Around 200mm (thanks Bernard) rain fell near Coverack in this afternoons major thunderstorm. Almost all the rain fell prior to this morning Weather Warning start, which was 17:00, by which time the sun was back out in Coverack. The most severe period was 14:00-16:00,


Graham
Penzance

The official figure for the Coverack storm, seems to be just over 100mm, but I've now seen 2 separate reports indicating 160mm & 170mm. A small patch of torrential rain & large hail barely moved for some time.

The 170mm is essentially based on a bucket - but in the absence of anything else. https://www.coverack.org.uk/pages/news.html

Culdrose received 1mm during the period.

Graham
Penzance

I should have included this:-

"Rainfall amount Mathematical challenge.
Tuesday 18th July 2017 in the afternoon
A three gallon builders’ bucket was used in the morning to carry wood chippings.
It was left empty in a space over two metres away from the nearest building.
On the evening of the same day the bucket contained water to a depth of 232mm.
The diameter of the top of the bucket was 310mm, with a lip to pour contents for
about one eighth of its circumference (120mm)
The volume of water contained in the bucket, measured the next day, was 13.014
litres. There was no perceptible change in level overnight.
This was measured by weighing the water in the bucket on bathroom scales 13.6Kg,
and subtracting the weight of the containing vessel, 586g.
I believe this gives a result of about 173mm of rainfall.
If the amount of rain added by the shape if the lip is removed, then I believe that
reduces the amount of rainfall to about 170mm."

The 160mm figure nearby was derived in a similar way.

Graham
Penzance
Graham,
Can you say where this came from as it appears to be the original source for a discussion I have seen elsewhere?
Thanks,
David

This is now linked from a few sites https://www.coverack.org.uk/Info17/R...hallenge .pdf It originally appeared on the Coverack Community website (coverack.org) The building work was taking place in the village.

I suggest you email **********************for more information. I also saw a report of 160mm in a bucket, but annoyingly I can't find it now.

Comparisons have been drawn, by the media, with the last (of many!) Boscastle flood. Apart from the rainfall intensity, I think there are significant differences. The last Boscastle storm was really triggered (in my opinion) by the north coast sea breeze onset, a feature of most big N Cornwall coast storms (like this http://www.turnstone-cottage.co.uk/SrMerrynStorm.PDF ) Also the geography is very different. Boscastle is in a narrow very steep valley with little soil. Coverack is quite open, with fertile land & fields behind, with lots of small streams. This makes the event rather more surprising.The roads tended to trap and guide the water, hence a lot of the damage.

Graham

Thanks.

I've been to Boscastle but I can't recall going to Coverack. Something worth mentioning might be that the rainfall from the MCS may well have 'prepped' the catchments then the back-building storm overwhelmed them. There's no evidence at present boundary layer conditions a played a significant role as at Boscastle as the storm was elevated and effectively cut off from the surface. A short-wave trigger was involved in both however.