11th June 2015 - Sudden Cold Front?

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11th June 2015 - Sudden Cold Front?

Postby Nick Gardner » 2015 Jun 12, 13:45

A lovely warm evening yesterday so we had dinner outside. The sky was overcast but dry, temperature was 20°C, barely a breath of wind and a DP of 14°C made for a perfect evening.

Then at 21:20 you could suddenly hear the wind in the trees further down the valley, it was approaching at quite a pace. The wind went from near calm as it had been all evening to a mean wind speed of 22 mph almost instantly. The temperature dropped from 20°C down to 16°C and there was a notiecable drop in humidity too.

No rain fell and whilst the sky was over-cast there was no change in the uniform grey of the clouds. The air felt very different and it went from being a warm evening to one with a 'chill' in the air which brought about a rapid abandonement of dinner outside. Despite the temperature only dropping to 16°C, it felt much colder.

The wind slowly subsided and there was a recovery in the humidity. The air pressure was steady at 1011.0 hpa and the wind was from an easterly direction. When the wind suddenly picked up the air pressure rose quickly to reach 1012.5 hPa in 30 minutes before slowly dropping back to 1011.0 at 23:35. The wind direction changed to a southerly at 21:25 and then back to an easterly at 22:00 accompanied by a quick drop in speed.

I've experienced such abrupt wind and temperature change during the latter part of a thunderstorm but there was no thunder, no lightning or rain.

The graph below shows the data from my Davis AWS.
ottervalley11thjune2015.png (59.68 KiB) Viewed 1379 times
Near Newton Poppleford, Sidmouth - Devon
50:41N 3:17 W; 20 metres AMSL; Station Grade B-BAAA37
Nick Gardner
Posts: 429
Joined: 2012 Jan 27, 17:25
Location: Rural riverside valley location near the village of Newton Poppleford and 2 km from the sea.

Re: 11th June 2015 - Sudden Cold Front?

Postby greg_gruner » 2015 Jun 12, 20:22

Very interesting, Nick. I don't really have an answer, but I would imagine that the developing low in the Bay of Biscay caused some high level instability, with pressure fluctuations and hence sudden wind changes. With the low overcast you couldn't really see any cloud activity at a higher altitude, but I'm pretty sure that was where the sudden changes came from. Doesn't sound like a sea breeze as you had no sunshine and the dew point dropped as well.
Greg Gruner
Farnborough, Hampshire
Posts: 224
Joined: 2012 Feb 04, 17:28

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