scuse my ignorance - what does PVA stand for/mean?

Jim.

"keith.r.harris" wrote in message
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Thanks Paul, I should look at those WV images more often. I must admit I
realy need to get my head around the links with jets PVA's and upper
troughs
as there's obviously a lot to be gleaned from this understanding.

Keith (Southend)
http://www.southendweather.net

"PJB" wrote in message
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