Martin Rowley wrote:

Norman wrote:
Martin Rowley wrote:

On Dec 26, 8:59 pm, "Colin Youngs" wrote:
Sunday 26th December 2010
snip
UK min. temps on Saturday night http://tinyurl.com/2auy3y8
snip
Sennybridge -13.3 C, Castlederg and Shawbury -15.1 C, Hereford
snip
Reported rainfall totals in 24 hours ending 18.00 UTC on Sunday
snip
Wick 11 mm, Ballypatrick 13 mm, Castlederg 19 mm.
[and]

David G wrote:

Castlederg -16 deg min and 19mm rain equivalent seems anomalous ?

... from the SYNOPs in the 24hr to 1800Z (26th Dec), the minimum
temperature reported was set the previous evening (25th) around 21Z; the
temperature rose above zero degC between 06 & 07Z today (26th) and rain
started around 12Z today - quickly becoming occasional moderate. No doubt
the precipitation figure for the 24 hours is composed of a mix of
rainfall between 12 & 18Z and melted snow remaining in the gauge.

We're going to get quite a number of 'anomalous' rainfall data reports
from the many automatic stations dotted about - caution required :-)

Martin.

Do you know how this is treated "officially" Martin? Do the totals as
measured become the "official" record? If so, a day of heavy snow and below
zero temps would go down as a dry day and a day of no precipitation in a
thaw might go down as a wet day. There would also be significant
precipitation "loss" on days of strong wind with heavy snow and below zero
temps when very little accumulates in the funnel. This can have legal
implications as "official" weather measurements are often presented in
Court as "fact". It also highlights the difficulty in comparing recent
winter rainfall measurements that rely on AWS with past rainfall
measurements using manual gauges.

... I wish I knew Norman but I suspect such data don't influence the
permanent record as much as you might think. What I do know is that the
observations are just one (small) part of the mix which go to making up the
'official' record. For example, if you have an insurance claim that happened
to be within spitting distance of, say, Brize Norton, then the 'real' BZN
observations would not be used/provided as such, but the gridded data-sets
resolved to a local mesh (2 km according to this link, but it may be finer),
and that is the data that would be the 'official' weather for that spot:-


It would make for an interesting legal argument if, in the example you cite,
the BZN observations were significantly different to the gridded data.

I haven't yet come across the gridded data in any of the cases that I have
worked on. Contrary to what you say above, I do still often see raw
observations, provided by the Met Office without comment or interpretation, but
often mis-interpreted by experts of other disciplines and by barristers. I'm
not sure how well the gridded data would stand up in Court given that the Met
Office will not provide anyone to explain and support it there. It's not fact
so it can't really stand up on its own without expert support.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.