In uk.sci.weather on Sun, 8 Aug 2004 at 12:54:00, Alan Gardiner wrote :

Dewpoint dropped to 4°C

Surely not? There's been no CF that I've seen?

this afternon from 17°C this morning in St Albans.

In another post John O'Rourke reported a depoint of 2°C at Heathrow at
14:50; this is about 20 miles from here so I have no reason to think
myreading was incorrect.

But what could cause such low dewpoints in the midst of such a warm &
humid spell?
--
Paul Hyett, Cheltenham