Highly variable winds - Thursday 12 June

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Highly variable winds - Thursday 12 June

Postby Stephen Burt » 2014 Jun 12, 21:30

Winds very light and very variable here today, in the middle of an anticyclone. My AWS (wind vane and anemometer at 11 m AGL) records wind speed and direction continuously, and logs every minute. From the logged records, the wind direction has made five complete 360 degree rotations during daylight hours today. Highest gust only 8 kn, highest hourly mean only 2.5 kn.

I've seen two or three complete revolutions in a day before, but I think five is probably a new record of sorts!

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: Highly variable winds - Thursday 12 June

Postby Graham Easterling » 2014 Jun 13, 16:02

A typical 'centre of a sunny high' sequence of events here, where there is a distinct sea breeze cycle.

The south coast sea breeze kicks in 1st, due to the morning sun. The NW facing north coast sees strongest heating PM, and a later sea breeze. So in Penzance on Thursday there was a moderate onshore sea breeze from noon to 17:00, then it was calm, then around 18:30 the north coast sea breeze reached the south coast, as it frequently does early evening.

This meant that in Penzance the temperature reached 20.2C around noon, fell back to near 18C mid afternoon, then reached the maximum of 20.5C at 18:30.

It's particularly interesting at Marazion, where the low marsh across to the Hayle estuary means the onshore breeze is often replaced by the north coast breeze as early as mid afternoon. Confusing to holidaymakers who suddenly find themselves the wrong side of a windbreak.

Today, the generally N gradient wind meant no sea breeze on the south coast, and the warmest day of the year so in Penzance, much cooler on the north coast, so:-

Max temperatures away from the north coast:-
Culdrose 22C
Penzance 22.7C

Near the north coast
Camborne 17.5C (used by the MetO for 'recent Penzance weather' - when in reality a difference of 5C is not uncommon. Culdrose would generally be a far better match, if a little on the low side)
Right on the north coast, a particular exposed cliff top site, The Island, St Ives 17C

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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