On Sun, 30 Jul 2017 19:23:21 +0100, N_Cook wrote:
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.
Thanks for that, it's useful to have corroboration of my
observations... and St. Denys is 6 miles NW of here so it wasn't a
very small local effect. Both events being completely missed by the
rainfall radar is in my experience here very unusual, unique in my
experience even in torrential rainfall. The 18 July event was similar
but the divergence seems to have been much less extreme in scale.
I wonder if others have experienced this kind of anomaly?
--
Dave
Fareham (W)