To be honest Paul, I'm rather puzzled as to why the high is collapsing
so quickly. Only thing I can think of is forcing from the broadscale
upper flow at and above the jet stream level. What should we look for ?
Well I normally look for a strong south to north jet to the west of the
high and a cold plunge to the east and preferably a slow moving vortex/
depression to the south of the high centre. I guess it was the first
condition that we didn't properly get this time. Point a strong jet
straight at a high and it often collapses, but not always, sometimes
the jet splits and that helps to reinforce it so it is a fine balance
and the mechanisms of blocking and block breakdowns are still not fully
understood. What goes on at the tropopause is thought to be important
nowadays.

Best I can do.

Cheers,

Will (Haytor, Devon)
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