Dave Ludlow wrote:

On Sat, 21 Apr 2018 23:23:38 +0100, N_Cook wrote:

So about 28mm in 55 minutes with a peak rate of 200mm/hr

A PWS in Bitterne reports 68mm - peaking 223 mm/h and almost all
during that late evening thunderstorm, with one at Midanbury 53mm and
both are supported by the rainfal radar accumulated precipitation
estimates.

Only 7 mm here in W Fareham but boy was that a spectacular horizon to
horizon lightning spectacular, lasting about 45 minutes with mostly
c-c flashes every second or two at times. It may only be April but I
haven't observed a 'summer' thunderstorm like that for donkeys years -
brilliant!

Yes, the yellow warning issued yesterday morning got it completely
wrong. The prediction was for all the action to be in the north of
England while the south didn't get a mention. The warnings didn't catch
up until yesterday evening when the event was actually developing in
the south.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr

On 22/04/2018 00:32, Dave Ludlow wrote:
On Sat, 21 Apr 2018 23:23:38 +0100, N_Cook wrote:

So about 28mm in 55 minutes with a peak rate of 200mm/hr

A PWS in Bitterne reports 68mm - peaking 223 mm/h and almost all
during that late evening thunderstorm, with one at Midanbury 53mm and
both are supported by the rainfal radar accumulated precipitation
estimates.

Only 7 mm here in W Fareham but boy was that a spectacular horizon to
horizon lightning spectacular, lasting about 45 minutes with mostly
c-c flashes every second or two at times. It may only be April but I
haven't observed a 'summer' thunderstorm like that for donkeys years -
brilliant!


I don't know what the peak lightning strike rate was but that IoW site
gave 76 strikes per minute at 22:51, with 31 mile range setting.
Now to retrospectively work out what the likely rise in the deep-level
sewer system probably was, using previous data obtained in daylight
hours. A few thousand old-stock homes that discharge roof rain into the
sewer system. The deep system interconnects with the local sewer system,
and , which it should not do, couples to the storm drain system that is
open to the nearby tidal river due to failed outlet flap valves, due to
dilapidations in the pipe-runs.

On 21/04/18 23:23, N_Cook wrote:
So about 28mm in 55 minutes with a peak rate of 200mm/hr

Reminded of some crap we were taught on the assistants' course in 1962,
one of several piles dumped on us. We were told never to report a
violent shower as we never get that in this country, it only occurs in
the tropics. I thought it was nonsense at the time and have been proven
right on many occasions.

For the record, a violent shower is classified in my "notes for
scientific assistants" as having an intensity of "greater than about
50mm (2 inches) per hour". ["Greater than about"? what?]

Heaviest rain I witnessed brought visibility down to 200m, which is not
often seen in snow let alone rain. Don't know the rainfall rate (I was
sitting in my stalled car outside the tower waiting for it to ease off)
but the observer said the tipping-bucket-rain-gauge counter "sounded
like a machine gun". That was on a cold front.

--
Graham P Davis, Bracknell, Berks. Web-site: http://www.scarlet-jade.com/
"There is nothing more frustrating than playing hide and seek with a
deaf wolf." [Benton Fraser]
OS: Linux [openSUSE Tumbleweed]

In a different context Matt Taylor mention Bude, which he said was in Devon. Maybe they've moved the border - or maybe the town. Who knows?

Tudor Hughes, Hamsey Green, Warlingham, Surrey 557 ft, 170 m.

David Braine, on the BBC SW forecast on Thursday (based in Plymouth), said "It's been foggy along the north Cornish coast today, as you can see from this picture of Porlock sent in by one of our weather watchers..."

On the plus side, the photo did appear to be of Porlock.

Well to the west of any thunder here.

Graham
Penzance

On Sunday, 22 April 2018 07:21:35 UTC+1, Norman Lynagh wrote:
Yes, the yellow warning issued yesterday morning got it completely
wrong. The prediction was for all the action to be in the north of
England while the south didn't get a mention. The warnings didn't catch
up until yesterday evening when the event was actually developing in
the south.

--
Norman Lynagh

Just 0.1mm overnight here. Distant lightning in the early hours, but no thunder heard.
Ken
Copley
Teesdale

In message , Dave Ludlow
writes
On Sat, 21 Apr 2018 23:23:38 +0100, N_Cook wrote:

So about 28mm in 55 minutes with a peak rate of 200mm/hr

A PWS in Bitterne reports 68mm - peaking 223 mm/h and almost all
during that late evening thunderstorm, with one at Midanbury 53mm and
both are supported by the rainfal radar accumulated precipitation
estimates.

Only 7 mm here in W Fareham but boy was that a spectacular horizon to
horizon lightning spectacular, lasting about 45 minutes with mostly
c-c flashes every second or two at times. It may only be April but I
haven't observed a 'summer' thunderstorm like that for donkeys years -
brilliant!


I wonder how many years back you would have to go to find a comparable
UK April thunderstorm.

Though we had a shower yesterday evening here in Cranleigh, I didn't
notice any lightning (but the curtains were drawn) or hear any thunder.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

On 22/04/2018 08:16, Graham P Davis wrote:
On 21/04/18 23:23, N_Cook wrote:
So about 28mm in 55 minutes with a peak rate of 200mm/hr

Reminded of some crap we were taught on the assistants' course in 1962,
one of several piles dumped on us. We were told never to report a
violent shower as we never get that in this country, it only occurs in
the tropics. I thought it was nonsense at the time and have been proven
right on many occasions.

For the record, a violent shower is classified in my "notes for
scientific assistants" as having an intensity of "greater than about
50mm (2 inches) per hour". ["Greater than about"? what?]

Heaviest rain I witnessed brought visibility down to 200m, which is not
often seen in snow let alone rain. Don't know the rainfall rate (I was
sitting in my stalled car outside the tower waiting for it to ease off)
but the observer said the tipping-bucket-rain-gauge counter "sounded
like a machine gun". That was on a cold front.

I've mentioned this before, but we had a Jardi rate of rainfall recorder
at Kew Observatory (6ft diameter collector). This recorded up to 200mm
and hour. We also had other weird and wonderful rain rate and rain
amount recorders as well. We had a list of occasions where the rate was
measured (not estimated) at over 100mm per hour. But when the DWR
(remember that?) was published we only had pR printed. I issued a
correction only to be told what you were. It was very gratifying to
disabuse them of their incorrect notion. The real reason was they
couldn't print the 2 subscript.
This, of course, was only one station....

A Southern Water contractor at the small group of lowest lying houses
this morning in St Denys , Southampton, sorting out their sewage
problems from last night, the main group of slightly higher level houses
escaped this one.

From previous measurements I reckoned about 12 minutes of 180mm
average/hr rain or 36 minutes of 60 average mm/hr rain would reach house
floor levels, ignoring air pressure imbalance issues.
Totally ignoring the 20:00 rain as plenty of time for the Archimedian
screws of the local sewage works to handle that, back to normal levels.
From the local retired professional metman's rainfall bucket gauge I
reckon graphically from about 22:15 something like 20 mins of 55 average
mm/hr, 4 min of 90 av mm/hr, 9min of 150mm av /hr,4 min 130 av mm/hr
,4min of 75 av mm/hr.
The 20 minutes of rain would have pre-charged the system and then
dropped back somewhat during the lull about 22:40, no idea how to allow
for that.
But 9mins of 150mm av/hr on its own probably means about 2/3 of the
headroom available before residential floor level reached.

On 21/04/2018 19:13, Graham Easterling wrote:
Certainly lively over Devon now, Nick G might be posting soon.

Spent the evening round my parents who live a couple of miles away so no
postings from me.

There were rumbles of thunder on and off through the evening but nothing
came close. Plenty of activity on my lightning detector just to the west
of here and out of over Lyme Bay.

Then later in the evening another cluster of storms over Hampshire way.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

Graham P Davis wrote:

On 21/04/18 23:23, N_Cook wrote:
So about 28mm in 55 minutes with a peak rate of 200mm/hr

Reminded of some crap we were taught on the assistants' course in
1962, one of several piles dumped on us. We were told never to report
a violent shower as we never get that in this country, it only occurs
in the tropics. I thought it was nonsense at the time and have been
proven right on many occasions.

For the record, a violent shower is classified in my "notes for
scientific assistants" as having an intensity of "greater than about
50mm (2 inches) per hour". ["Greater than about"? what?]

Heaviest rain I witnessed brought visibility down to 200m, which is
not often seen in snow let alone rain. Don't know the rainfall rate
(I was sitting in my stalled car outside the tower waiting for it to
ease off) but the observer said the tipping-bucket-rain-gauge counter
"sounded like a machine gun". That was on a cold front.

Just after 1630z this afternoon we had a shower in Tideswell with a max
rate briefly of 57 mm/hr. It really did hammer down for a minute or so.
Not particularly unusual, though.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr