On Tue, 10 Mar 2015 08:49:29 +0000, Alan
wrote:
Some years ago, and I copied the correspondence to this group, I
took
issue with the MO over their warning policy pointing out that a
'yellow'
for 25mm of rain for this area would probably warrant an 'amber' or
even
'red' for somewhere like Essex. I think they conceded the point
but, for
consistency, applied the same criteria over the whole of the UK.

Seemed a bit daft to me, but then lots of things do.

The warning level is based on impacts rather than thresholds on
meteorological parameters.

A case in point was the amber rain warning last week, whereby the
amber area was different to the area that was forecast to receive the
most rainfall. This was because the impact from the rainfall was
assessed to be higher in that different area - namely where runoff
from the rainfall (and effects arising from it - such as landslides)
would affect populated areas and well-used roads.

200mm of rain in Essex would be very likely to have a much bigger
impact there than in the north-west highlands (think about the
Tewkesbury area in 2007), so would probably have warranted a red
warning.

I can think of other examples - but the message I am trying to convey
is that it should be the impact rather than the actual meteorological
values that is important - and the warning system reflects this.

--
Freddie
Pontesbury, Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
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