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.

That reminds me: I haven't seen a really good 'jiggly' barograph trace
from a series of thunderstorms for a long time now. Must be overdue.

No sign of the Northern England rapid drop this morning down this way
(fairly steady 8 mbar fall 22-04z, then fairly steady 1001-1002 mbar
until a rise set in 13z), so there must have been a significant
additional gradient somewhere for a while ...

--
Stephen Burt
Stratfield Mortimer, Berkshire