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Graham P Davis · May 29th 08, 05:53 PM posted to uk.sci.weather

wrote:

On 28 May, 14:38, Tudor Hughes wrote:

It sounds as if it was thunderstorm-related but extremely rapid
falls can be caused by gravity waves. * One of these affected west
London (Sunbury) on about 19 Jan 1977. * We had a mercury barometer in
the laboratory and you could actually just about see the mercury
surface falling. *I cannot remember the exact figures (it has been
written about, probably in "Weather") but 8 mb in 5 minutes seems to
ring a bell. *There were gusts to 30 kn but nothing more in an
otherwise breezy cloudy SW'ly. *The expected End Of The World did not
happen.

Tudor Hughes, Warlingham, Surrey

Well-remembered, Tudor. (It was actually the 25th of January, but
what's six days in 31 years ... !) Heathrow had a fall of 7 mbar in 5
min and I can recall first-hand accounts of the duty observers
thinking either all their barometers had broken at the same time, or
the world/their career/their life was ending, or quite possibly all
four. Must have been hairy on final approach I'm sure. Reference in
Weather for those who want to look it up:

Harvey, I. G. and Warren, D. E. (1978) Observations of rapid pressure
variations: 25 January 1977. Weather, 33, pp. 11-17.

I was at Wattisham at the time and was drawing up a chart when I glanced at
the anemograph next to me. I asked the assistant, who was sending the
hourly ob to Air Traffic, to read the the pressure again. He asked why but
I just asked him to humour me. He read it, looked at the 2309 copy and the
register, then read it again. The pressure drop was 7mb. He called the info
to ATC and whilst he was sending the hard copy to them I suggested he read
it again - it had bounced up again by 5mb. During this, the wind rose by
about 10kt and we went into fog. A bit of a shock when you're in a warm
sector and expecting a nice boring day!

--
Graham P Davis, Bracknell, Berks., UK. E-mail: newsman, not newsboy.
"What use is happiness? It can't buy you money." [Chic Murray, 1919-85]