"Joe Hunt" wrote in message
...

Snip
Bristol may have been a foci of moisture due to surface
convergence and hence all the "ingredients" occurred here first.

Localised convergence (among other factors excellently detailed by Joe) was
evident at 1300Z and quite probably the key to the activity that developed
near Bristol and extended NE as an apparent MCS.

The 1300Z streamline analysis/conveyance can be seen here :-
http://www.metbrief.com/13z.gif

Jon.