"Waghorn" wrote in
:

Hi Rich,
my view on this is that this was a squall line event forced by a low
level cold front propagating as a gravity current.Frictional effects,as
the cold air headed south,wld've sharpened the frontal boundary.I'm not
sure about the role of the upper air,though mode of propagation of the
GC is sensitive to enviromental shear,and p'haps some tropopause
folding occured as well.It's possible the Chilbolton image I pointed
out shows this GC head.

Hi Dave

I imagine the colder denser air behind the cold front could well have acted
as a density current, especially when augmented by sublimation of the snow
falling from the cloud above - I think the mechanism for this sort of front
was still in question when I left it, one author tried to rubbish the
density current idea, others still held on to it.

Plenty of upper level support for this one, look how the dry slot
dramatically appears in the imagery between 1130 and 1730. It may be that
the dry air overran the surface front as well as dug in behind, causing some
convective instability that led to the storms? Plenty of food for thought.

http://meteosat.e-technik.uni-ulm.de...V/E2/20040128-
1130-WV-E2.gif
http://meteosat.e-technik.uni-ulm.de...V/E2/20040128-
1730-WV-E2.gif

Cheers
Rich