58mph 0450 GMT Wincanton, Somerset
Alan
www.wincantonweather.org.uk

On Sun, 03 Dec 2006 09:27:10 +0000, alanwhitewick wrote:

58mph 0450 GMT Wincanton, Somerset

Mean or gust?

Personally I feel that the quoting of gust speeds is rather meaningless
and rather tabloid mejia like. An accompanying mean would mitigate that
somewhat. Case in point the lone 57mph gust here at 0259, was that real
or a instrumentation glitch? Other gusts at that time where the low 50's
mph.


--
Cheers
Dave. pam is missing e-mail

On Sun, 03 Dec 2006 11:08:44 +0000 (GMT), "Dave Liquorice"
wrote:

Mean or gust?

Personally I feel that the quoting of gust speeds is rather meaningless
and rather tabloid mejia like. An accompanying mean would mitigate that
somewhat. Case in point the lone 57mph gust here at 0259, was that real
or a instrumentation glitch? Other gusts at that time where the low 50's
mph.

I tend to agree.

Lone gusts are exciting to quote but don't really give a true picture
which is better represented by, say, a fifteen minute mean.

In my [WR]s I quote a previous hourly mean based on fifteen minute
means, a previous hourly mean gust based on fifteen minute maximum gusts
and maximum gust for the period since 00:00z. This, I think, gives a
better subjective appreciation of what is actually happening.

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather
Some walks and treks:- http://windycroft.gt-britain.co.uk/walks

"Dave Liquorice" wrote in message
ll.com...
On Sun, 03 Dec 2006 09:27:10 +0000, alanwhitewick wrote:

58mph 0450 GMT Wincanton, Somerset

Mean or gust?

Personally I feel that the quoting of gust speeds is rather meaningless
and rather tabloid mejia like. An accompanying mean would mitigate that
somewhat. Case in point the lone 57mph gust here at 0259, was that real
or a instrumentation glitch? Other gusts at that time where the low 50's
mph.



Dave, it is the gusts that do the damage. Your gust was probably true as is the
nature of gusts especially in the met. conditions of last night with long lulls
then powerful gusts. For the record, my 3m agl mean at max gust time of 41 knots
was a mere 17 knots. The 17 knots, does of course correct up to 29 knots at 10
metres agl. So a force 7 with powerful gusts running at 2.4 above the mean speed
(which was characteristic of the night I think). That was my site which is
fairly sheltered by a slope to my south and west, the open moor would have been
wild!

Will.
--

Will Hand wrote:



Dave, it is the gusts that do the damage. Your gust was probably true as is the
nature of gusts especially in the met. conditions of last night with long lulls
then powerful gusts. For the record, my 3m agl mean at max gust time of 41 knots
was a mere 17 knots. The 17 knots, does of course correct up to 29 knots at 10
metres agl. So a force 7 with powerful gusts running at 2.4 above the mean speed
(which was characteristic of the night I think). That was my site which is
fairly sheltered by a slope to my south and west, the open moor would have been
wild!

Will.

Hello again, Will,

(Retired headteacher writing here and therefore not a meteorologist) -
humble mode off.
According to my bible - Met O Observers handbook,
MWS at 3 metres needs +20% for 10 metre conversion.
Thus your 17KT would come out at only 20KT at standard height.
Of course, a 10 metre pole is still not sufficient as it has to be an
effective height of 10 metres.
Met O told me that at least 15 metres would be needed here even in this
exposed location.

Full list for those interested,
Effective height Correction
1 - 2 metres add 30%
3 - 4 metres add 20%
5 - 7 metres add 10%
8 - 13 metres no correction
14 - 22 metres subtract 10%
23 - 42 metres subtract 20%
43 - 93 metres subtract 30%

The full formula is explained together wit reciprocals etc but I'm a
bit out of depth with that.
There is a separate table for wind over sea.
Gust speeds at reported wothout correction.

Best wishes,
Ken
Copley, nr Barnard Castle, Teesdale, County Durham
http://copley.mysite.orange.co.uk

"Alan White" wrote in message
...
On Sun, 03 Dec 2006 11:08:44 +0000 (GMT), "Dave Liquorice"
wrote:

Mean or gust?

Personally I feel that the quoting of gust speeds is rather meaningless
and rather tabloid mejia like. An accompanying mean would mitigate that
somewhat. Case in point the lone 57mph gust here at 0259, was that real
or a instrumentation glitch? Other gusts at that time where the low 50's
mph.

I tend to agree.

Lone gusts are exciting to quote but don't really give a true picture
which is better represented by, say, a fifteen minute mean.

In my [WR]s I quote a previous hourly mean based on fifteen minute
means, a previous hourly mean gust based on fifteen minute maximum gusts
and maximum gust for the period since 00:00z. This, I think, gives a
better subjective appreciation of what is actually happening.


Alan, yes the fuller the picture the better. At what height are your wind speeds
recorded? I am going to make sure it is very clear on my own web site, for
example, that they are measured at 3m agl as it is clear from all the reports
today that anemometers are at varying heights making comparison difficult unless
thay are corrected to 10m (which requires expertise).

Will.
--

On Sun, 3 Dec 2006 12:25:16 -0000, "Will Hand"
wrote:

Alan, yes the fuller the picture the better. At what height are your wind speeds
recorded?
...

see http://windycroft.gt-britain.co.uk/P8280559.jpg

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather
Some walks and treks:- http://windycroft.gt-britain.co.uk/walks

"Ken Cook" wrote in message
ps.com...

Will Hand wrote:



Dave, it is the gusts that do the damage. Your gust was probably true as is
the
nature of gusts especially in the met. conditions of last night with long
lulls
then powerful gusts. For the record, my 3m agl mean at max gust time of 41
knots
was a mere 17 knots. The 17 knots, does of course correct up to 29 knots at
10
metres agl. So a force 7 with powerful gusts running at 2.4 above the mean
speed
(which was characteristic of the night I think). That was my site which is
fairly sheltered by a slope to my south and west, the open moor would have
been
wild!

Will.

Hello again, Will,

(Retired headteacher writing here and therefore not a meteorologist) -
humble mode off.
According to my bible - Met O Observers handbook,
MWS at 3 metres needs +20% for 10 metre conversion.
Thus your 17KT would come out at only 20KT at standard height.
Of course, a 10 metre pole is still not sufficient as it has to be an
effective height of 10 metres.
Met O told me that at least 15 metres would be needed here even in this
exposed location.

Full list for those interested,
Effective height Correction
1 - 2 metres add 30%
3 - 4 metres add 20%
5 - 7 metres add 10%
8 - 13 metres no correction
14 - 22 metres subtract 10%
23 - 42 metres subtract 20%
43 - 93 metres subtract 30%

The full formula is explained together wit reciprocals etc but I'm a
bit out of depth with that.
There is a separate table for wind over sea.
Gust speeds at reported wothout correction.


Thanks Ken, that looks familiar :-)

However, those formulae are very generalised and must assume a roughness length
that may or may not be representative of the site. Roughness length also varies
with wind direction/fetch. The general relationship (without roughness length)
is a logarithmic increase with height, now very roughly log(10)/log(3) = 1/0.48
= 2.08 . i.e. 10 metre wind = 2.08 x 3 metre wind, but this factor will be
reduced according to roughness. If we introduce a roughness length of 0.3 then
the factor becomes log (10/0.3)/log(3/0.3) = 1.53. The figures you quoted may be
OK for a well exposed open site with few obstacles but for rough terrain and in
built up areas they will be way out. I guess if you a proper MetO vetted site
then you would be well exposed. As for gust I can understand the reason for
using un-corrected values as in a well exposed site the momentum *may* not be
reduced much, but again in a "rough" site they will dissipate more.

I really must get that 10 metre mast!

Thanks,

Will.
--

Ken Cook wrote:
Will Hand wrote:

Dave, it is the gusts that do the damage. Your gust was probably true as is the
nature of gusts especially in the met. conditions of last night with long lulls
then powerful gusts. For the record, my 3m agl mean at max gust time of 41 knots
was a mere 17 knots. The 17 knots, does of course correct up to 29 knots at 10
metres agl. So a force 7 with powerful gusts running at 2.4 above the mean speed
(which was characteristic of the night I think). That was my site which is
fairly sheltered by a slope to my south and west, the open moor would have been
wild!

Will.

Hello again, Will,

(Retired headteacher writing here and therefore not a meteorologist) -
humble mode off.
According to my bible - Met O Observers handbook,
MWS at 3 metres needs +20% for 10 metre conversion.
Thus your 17KT would come out at only 20KT at standard height.
Of course, a 10 metre pole is still not sufficient as it has to be an
effective height of 10 metres.
Met O told me that at least 15 metres would be needed here even in this
exposed location.

Full list for those interested,
Effective height Correction
1 - 2 metres add 30%
3 - 4 metres add 20%
5 - 7 metres add 10%
8 - 13 metres no correction
14 - 22 metres subtract 10%
23 - 42 metres subtract 20%
43 - 93 metres subtract 30%

The full formula is explained together wit reciprocals etc but I'm a
bit out of depth with that.
There is a separate table for wind over sea.
Gust speeds at reported wothout correction.

Best wishes,
Ken
Copley, nr Barnard Castle, Teesdale, County Durham
http://copley.mysite.orange.co.uk

Hi
In response to some of the comments, my anemometer is set at 5m agl
and quite exposed.
Between 0340 and 0500 GMT this morning, gusts of 50mph, 51mph, 54mph
55mph and 58 mph were recorded. Mean wind speed during this period was
at 33mph.(corrected to the notes above gives 37mph)
As stated it is the gusts that cause damage. During this period a few
trees and fences were brought down. There were two large flashes in the
sky, no doubt caused by power lines, as there was no lightning.
Power went off for about 10 minutes.

Alan
www.wincantonweather.org.uk

In article om,
Dave Liquorice writes:
On Sun, 03 Dec 2006 09:27:10 +0000, alanwhitewick wrote:

58mph 0450 GMT Wincanton, Somerset

Mean or gust?

Personally I feel that the quoting of gust speeds is rather meaningless
and rather tabloid mejia like. An accompanying mean would mitigate that
somewhat. Case in point the lone 57mph gust here at 0259, was that real
or a instrumentation glitch? Other gusts at that time where the low 50's
mph.


But isn't it the gusts that are going to do most of the damage? That
seems to me to justify quoting them, though not to the exclusion of the
mean speed.
--
John Hall
"Madam, you have between your legs an instrument capable
of giving pleasure to thousands and all you can do is scratch it."
Sir Thomas Beecham (1879-1961) to a lady cellist