80mph gust for Penzance?

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80mph gust for Penzance?

Postby Graham Easterling » 2012 Nov 21, 11:02

Well, that's what the MetO is predicting, ( http://www.metoffice.gov.uk/public/weat ... ab=fiveDay it keeps changing though) which is strangely greater than that predicted for Lizard (and Penzance is relatively sheltered from the SW). The 5 day forecast frequently shows windspeeds in a F6-8 southwesterly the same in Falmouth & Penzance as the Lizard, which is clearly absurd.

I have never recorded anything near that on a SSW wind, it would = my all time record, and would smash the 73mph record for my current site, yet still no wind weather warning. I can only assume I'm not the only one who thinks it's unlikely. Even so it could be very interesting, bang on high tide. It might be worth keeping an eye on John Chappell's station near Gwennap Head, where 70mph gusts are far from unusual http://www.landsendweather.info/ (just click on readings.) in a SW he typically records gusts 25-35mph stronger than me.

The last (and only) time this century that gusts exceeded 70mph at my station was March 2008, when this occured on windward coasts http://www.youtube.com/watch?v=voKZuNlB4QU & http://www.sennen-cove.com/ts06.htm .
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

Re: 80mph gust for Penzance?

Postby Stephen Burt » 2012 Nov 22, 18:46

I was informed recently by an impeccable source within UKMO that weather warnings are now not issued merely for a nominal 'weather threshold' (such as, say, 70 mph gusts, or 50 mm rain in 12 hours), but only when the weather is expected to have an impact - trees down, floods etc.

So it may be that, for a given wind threshold, you don't see weather warnings for SW England whereas you might for SE England ... That might explain the lack of warnings?

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: 80mph gust for Penzance?

Postby Graham Easterling » 2012 Nov 22, 19:31

I wasn't criticising the lack of warnings, rather more the wind gust forecasts, which were higher for Penzance than anywhere else in the SW, including St Mawgan, Scilly or Lizard. This despite the fact that Penzance is sheltered from the SW. These forecasts are computer generated, and I suspect the 'real people' involved didn't believe 80mph in Penzance was at all likely and therefore didn't issue a warning.

At 08:30 today the maximum gusts for Penzance were forecast to be 69mph @ 09:00 & 81mph @ noon. In fact my highest gust was just 44mph @ approx 11:30. This low figure was predictable (although obviously not to the computer model) because of the wind direction. Penzance town gets strongest gusts on SE or NW winds (onshore or funnelling down NW - SE orientated valleys.) The same landforms protecting it from a SW. Strongest gusts right on the Pz prom, where the wind did top F8, may well have hit 60mph today. For exposed cliff top locations, where the forecasts were lower than Penzance, they were accurate, e.g Scilly - forecast 67mph, max gust 70mph.

I struggle to understand models that can produce forecasts predicting higher winds for a town sheltered (relatively speaking) from the SW, than nearby exposed cliff tops.
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

Re: 80mph gust for Penzance?

Postby Stephen Burt » 2012 Nov 22, 21:02

Graham, the model spacing is 1.5-4 km, so the orography in the model resolution simply isn't capable of resolving the fine detail of sheltered town vs clifftops etc. I expect that gridpoints which are 'mostly sea' as opposed to 'mostly land' in Cornwall will show higher wind speeds, but probably nothing more local scale than that. With that resolution the gridpoint used for the 'Penzance' wind speeds may even be a couple of km offshore, or over a hilltop just inland.

I did see some interesting model output forecasts for the wind field around Weymouth for the summer Olympics sailing events in a recent RMetS Saturday meeting, where the grid length was 300 m (on a very limited model domain of 25 x 25 km, boundary conditions fed from the main UK model). This produced very plausible-looking wind structures around orography, coastal features etc, but it'll be a while yet before we have computers powerful enough to cope with a 300 m grid length for a UK area model!

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: 80mph gust for Penzance?

Postby Graham Easterling » 2012 Nov 23, 10:59

Thanks for your feedback Stephen.

A pleasant lull in proceedings today!
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall


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