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:-

http://www.metoffice.gov.uk/services/insurance/pricing

Perhaps that's why the Met Office have backed out of giving opinions on
weather-related events - more work for experts like yourself :-)

Incidentally, this not using the 'real weather' is of course at the
heart of the recent exercise to decide whether snow did or did not occur
at various points around the country; after all, when did you last see
anyone taking readings in the grounds of Buckingham Palace?


Martin.




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Martin Rowley
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