Chart Validity

[j_davey]

Hi all,

Quick Question Regarding Time Validity of Significant Prognostic & Wind Charts,

When a Chart is Valid say 18:00 , does this mean up until 18:00, between 12:00 and 18:00

or

Valid AT 18:00 ?

for example a 1hr flight departing 14:00, should they have 12:00 , 18:00 or both?

thanks,
-Jd

[Schibulsky]

Generally these charts show you the predicted wx at that time of validity, not for a range of time.
But as these charts are issued 6hrs apart we consider the "validity" +/-3hrs.
For your example the flight should carry 1200 and 1800.

[Lauderdale]

So just building on the previous posters comments:

Progs potray forecasts of selected weather conditions at specified valid times. Each valid time is the time at which the forecast conditions are expected to occur. A 12 hour-hr prog is a forecast of conditions which has a valid time 12 hours after the obeserved data base time, thus a 12 hr forecast. For example, a 12 hour forecast based on 00z observations is valid at 12z.

I guess you are asking this question based on the fact so what do I look at at 1132z? or 1035z?

The correct way is to treat exactly like FD forecasts: yes, interperlate....if on a 00z sig wx front 'A' is at X and on the 06z prog at Y then work on the basis that at 03z it is.....answers on a post card!

:ok:

[j_davey]

That answers my question nicely,

cheers lads.
-jd