"David Buttery" wrote in message


snip

Thanks. Actually, I was going to put a straight 40%, but this page:

http://www.crh.noaa.gov/lot/aviation/tafcode.html

says: "The PROB40 group is used when the occurrence of thunderstorms or
precipitation is in the 30% to less than 50% range" - and so I changed
my own translation to 30-50%.

Interesting. All I can say is that they do things a little differently
across the pond...

Also on that page is this statement "PROB40 will not be shown during the
first six hours of a forecast." I'd like to see the verification figures
!

They also tend to use FM a lot rather than BECMG (min 2 hour period, max
4) eg :-

(New York) KJFK 170914Z 170913 03021G32KT 6SM -RA BR OVC012 TEMPO 0913
3SM RA BR
OVC008 FM1400 02013G20KT 5SM -RA BR OVC012 FM2100 36011KT 5SM -RA BR
OVC020 FM0400 34009KT 5SM -RA BR OVC015

I've yet to reach that level of accuracy ;-)

Jon.




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