Rainfall radar limitations 30/07/17 (S Hants)
 

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?


St Denys, Soton, 1625 this afternoon ,intense rainfall peaking at
180mm/hr, 4mm in no more than 5 minutes, but nothing on the radar, no
pixel of any shade anywhere near. Again too small a scale presumably.