Originally Posted by bflyer
so when it states that the SIG WX is valid at for example, at 06 UTC, it means that the validity commences at 06 UTC
Originally Posted by HotDog
06UTC to 12UTC. Sawasdee.
No, not always.
SIGWX charts produced by WAFC London and WAFC Washington are
forecasts, not observations or reports. So that they may be used for flight planning.
Forecasts have a
validity periods spanning specified periods of time. Think about it -- if it didn't have a validity period, it would not be a forecast, you could not plan a flight with it, it would be useless.
SIGWX charts are an example of
point forecasts. A point forecast is a forecast expressed with a validity of a single date time group. But it is valid for a period of time, determined by the service provider or contracting state.
ICAO Annexe 3 (met services)
CHAPTER 9. SERVICE FOR OPERATORS AND FLIGHT CREW MEMBERS
9.6 Flight documentation —
significant weather charts
9.6.1 Where information on significant en-route weather phenomena is supplied in chart form to flight crew members before departure, the charts shall be significant weather charts valid for a specified fixed time.
4. Different providers/states sometimes use
different validity periods even though the validity time given appear the same.
Australian Bureau of Meteorology issue SIGWX at 00 06 12 and 18 hrs, valid 6hrs, being 3hrs either side of the published validity time. Therefore an Aussie BoM SIGWX chart that has 180600 as its validity is a forecast for the period 0300Z-0900Z on the 18th.
UK low level SIGWX... valid for 9hrs, being 4hrs before to 5hr after the validity time.. pls excuse lack of formatting...
Issued at/
Valid for Flights Between/
Validity Time/Outlook to/Prognosis
0330
0800 and 1700 1200 0000 1800
0930
1400 and 2300 1800 0600 0000
1530
2000 and 0500 0000 1200 0600
2130
0200 and 1100 0600 1800 1200
A pilot planning a flight on a SIGWX chart needs to look up the local AIP or WAFC decode and definitions and understand what period of time the SIGWX covers.