INSTRUMENTS FLIGHT PLANNING
The briefing void time for the DD 175-1 is normally one-half hour after the planned departure
time, not to exceed 2 ½ hours after the time of weather briefing. This may be extended if, in the
opinion of the meteorologist, the extension does not affect the quality of the forecast. The
forecast is considered to be valid for the period one hour before until one hour after the planned
arrival time at the destination or alternate.
In the event you are departing from an airfield with no weather briefing facility, telephone
briefings are available from both military and civilian facilities. Telephone numbers for military
briefing facilities are listed in the FLIP Flight Information Handbook and may be called collect.
The four categories of information available for preflight planning in the weather briefing office
Information received via teletype.
Information received via facsimile and/or automatic computer link.
Information prepared by local weather personnel.
Information which may be read from weather instruments.
Aviation Severe Weather Watch Bulletin (WW)
The National Weather Service issues unscheduled Weather Watch (WW) ("Willy-Willy")
whenever there is a high probability of severe weather development. These WWs are used to
forecast hazardous flying conditions for a designated area for a specified time period. The Air
Force issues scheduled Military Weather Warning Advisories. These graphical advisories are an
estimate of the weather producing potential of the existing air masses. These advisories are
given to all aviators filing from U. S. Air Force bases and are used for flight planning when
National Weather Service (WW) information is unavailable. Valid WW and MWA bulletins are
graphically displayed in all Navy and Marine Corp weather briefing offices. Air Force
advisories do not constitute a National Weather Service Aviation Severe Weather Watch
Bulletin. Except for operational necessity, emergencies, and flights involving all-weather
research projects or weather reconnaissance, pilots shall not fly into or through areas for which
the National Weather Service has issued an Aviation Severe Weather Watch Bulletin unless one
of the following exceptions apply:
Storm development has not progressed as forecast for the planned route. In such situations:
VFR filing is permitted if existing and forecast weather for the planned route permits
IFR flight may be permitted if aircraft radar is installed and operative, thus permitting
detection and avoidance of isolated thunderstorms.
IFR flight is permissible in positive controlled areas if VMC can be maintained, thus
enabling aircraft to detect and avoid isolated thunderstorms.
7-4 IN-FLIGHT WEATHER ANALYSIS