It has been raining here in Cumbria constantly since about 18:00 (not
drizzle, but proper, horrible rain), yet on the Met Office radar there
is no rain anywhere near us between 21:30 and 00:30. How large does
the area of rainfall have to be before it is detected by radar? Since
it has been raining non-stop for about 6 hours, I can't imagine that
it would be a small area of rain just stuck over the top of us!

Cheers,

Liam

P.S. I said it has been raining constantly since about 18:00, but it
would probably be more apt to say it has been raining constantly since
about July.

"Jack Frost" wrote ...
It has been raining here in Cumbria constantly since about 18:00
(not
drizzle, but proper, horrible rain), yet on the Met Office radar
there
is no rain anywhere near us between 21:30 and 00:30.
snip
.... you don't say whereabouts in Cumbria you are, but have just looked
at the Meteox archive ...

http://www.meteox.com/

and rain appears to be over or close-by Cumbria during the times
specified. Can't see archive of Met Office output.

There are good reasons why, sometimes, rain is not picked up properly
by the network - this file gives a good explanation ...

http://www.metoffice.gov.uk/corporat...actsheet15.pdf

Large parts of Cumbria are outside the medium-to-high resolution
footprint of the radar network, and at the longer ranges (relative to
the base station), the problem of the beam not picking up rain falling
in the lowest 1500 m or so is particularly apt ... see the text (about
2/3 down) for more on this ... however,

whether this was the case here I'm not sure. As I say, the Meteox
output appears to show rainfall.

HTH

Martin.



--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

In article , Martin Rowley
wrote:
"Jack Frost" wrote ...
It has been raining here in Cumbria constantly since about 18:00 (not
drizzle, but proper, horrible rain), yet on the Met Office radar there
is no rain anywhere near us between 21:30 and 00:30.

There are good reasons why, sometimes, rain is not picked up properly by
the network - this file gives a good explanation ...

When the air is wet at low levels with extensive stratus cloud, quite light
rain out of a fairly high base (seen by the radar) is considerably augmented
by the coallescence process at low levels. If there is a strong upslope wind
to maintain the low cloud then this augmentation can become really large.

I seem to recall that the maximum correction that could be applied in the
old FRONTIERS "nowcasting" system was in a SW gale and peaked at 8 mm/hr in
parts of the Lakes and Snowdonia. That is, the radar might see 1 mm/hr at
the cloudbase and in its scan, but 9 mm/hr might hit the ground out of sight
of the radar behind a range of hills. Much will depend on whether you see
"raw" radar data or corrected.

--
Rodney Blackall (retired meteorologist)(BSc, FRMetS)
Buckingham, ENGLAND
Using Acorn SA-RPC, OS 4.02 with ANT INS and Pluto 3.03j