On 30/07/2017 16:41, Dave Ludlow wrote:
Last night here in west Fareham we had two non-thundery torrential
downpours as the rain area crossed between 00:30 and 02:00 BST. The
first lasted 40 minutes and peaked at ~45mm/hour at 00:45 then tailed
off to stop briefly before resuming at 01:30.

The second downpour ended about 02:10 BST and peaked for a minute or
two at 100 mm/hour at 01:40 BST, roof gutters overflowed and it
looked and sounded as torrential as a thunderstorm would produce (no
hail though).

The above is from my VP2 bucket tips but I did empty the rain gauge
at 3 am and 21mm fell in those two 40 minute periods, just over half
in the second burst. However...

None of this was apparent on the (Netweather) 5 minute 500m rainfall
radar before, during or after the rain. The maximum rate shown for
here was (is still) ~8 mm/hour and the radar 24 hour total currently
for my location and nearby stands at ~10 mm (true total is ~24mm).

I assume that the heaviest part of the downpours were too brief to
register on radar - can anyone tell me if this is a common problem, as
I haven't noticed it occurring to this extent previously. Or is it
likely to be a rainfall radar calibration issue?


This site is run by a retired meteorologist type, St Denys Southampton.
, same 2 bouts of heavy rain this morning
http://www.seatern.org.uk/WCstdenys/WC/customgraph6.jpg
Evening of 18 July 2017, at 17:10 it read 120mm/hr for one spot reading
, but the radar image on this site showed no more than 25mm/hr for the
St Denys pixel at that time
https://max.nwstatic.co.uk
I assumed that very heavy rain blocks radar signals ie hiding even
heavier rain , just as it does visible light.

Does anyone know how to interpret , for a given road with a given slope,
the depth of rainwater running in the gutter, to a mm/hr measure? other
than cross-comparing with a local met site during various events.
Anyone know where to find better info than 2.82 inches for Southampton,
31 Oct 1953 , reported in the local press an event something like the
recent Coverack event, a wall of water coming down from higher ground,
with overloaded storm drain system