"martin rowley"

Jack (and all)
Not sure if this is the source Philip is using, but working through the
Meteograms section of this site, you can tabulate PPN accumulations from
the GFS output ...

http://www.arl.noaa.gov/ready/cmet.html

Yes. It does work (but of course no real rain here for next week!) I tried
it for a rainy area (the rains in Spain....)
and it is certainly possible, but far too tedious for everyday use. I
suppose as a one-off you might want to see how wet it will be for your
birthday......(or wedding, funeral, etc)

Jack