I was reading a post yesterday about the definition of a gale and the
'exaggeration' of some inland sites when reporting them.

I'm sure most amateur weather stations in domestic locations, even good
ones, suffer from having their anemometer below the standard WMO height of
10m. My Davis station was supplied with a tripod which reaches 2.5m. I was
able to get the anemometer to 4.5m by adding more poles but anything more
would both annoy my neighbours and probably require planning permission!

The Met Office's Observers Handbook contains a formula that provides an
approximate conversion from actual height to standard height. At 4.5m, this
is co-incidentally almost the exact reciprocal of the conversion from mph to
knots. Therefore my weather station set to mph provides an approximation to
the standard height in knots; quite handy.

The winter weather has still not reached Henfield (Sussex) by 12.45
(22/03/08). There was a recent heavy rain/hail shower but no sign of snow.
There's currently 7/8 Sc but there must be some Cb lurking somewhere....

Dave Parker

On 22 Mar, 12:44, "Dave Parker" wrote:
I was reading a post yesterday about the definition of a gale and the
'exaggeration' of some inland sites when reporting them.

I'm sure most amateur weather stations in domestic locations, even good
ones, suffer from having their anemometer below the standard WMO height of
10m. My Davis station was supplied with a tripod which reaches 2.5m. I was
able to get the anemometer to 4.5m by adding more poles but anything more
would both annoy my neighbours and probably require planning permission!

The Met Office's Observers Handbook contains a formula that provides an
approximate conversion from actual height to standard height. At 4.5m, this
is co-incidentally almost the exact reciprocal of the conversion from mph to
knots. Therefore my weather station set to mph provides an approximation to
the standard height in knots; quite handy.

The winter weather has still not reached Henfield (Sussex) by 12.45
(22/03/08). There was a recent heavy rain/hail shower but no sign of snow.
There's currently 7/8 Sc but there must be some Cb lurking somewhere....

Dave Parker

Don't forget that these 'corrections to standard height' apply only to
mean speeds, not to gusts, and they really only apply strictly to
heights in an unobstructed exposure (such as an open airfield) and in
conditions of average stability. They are of only limited relevance in
a turbulent environment such as suburban housing, and can give very
misleading results when applied in obstructed or sheltered exposures
or when wrongly applied to gusts.

Personally I suggest you are better leaving the wind speed unit
correct and taking the observed results 'as is', making appropriate
notes in your station metadata, website, etc etc about site, exposure
height and shelter etc, as using this coincidental approximation will
excessively inflate your gust speeds.

Incidentally my anemometer is at 11 m in a reasonably open exposure,
and in 15 years' observations here in Berkshire the wind has yet to
reach the definition of a gale viz. 34 kn mean over 10 minutes. So
'number of days with gale' here still stands at zero since 1993.

--
Stephen Burt
Stratfield Mortimer, Berkshire