A) If your destination airport does not have an instrument
approach or
Does not meet the 1 2 3 Rule.
1 hour before to 1 hour after ETA the destination airport must
have at least a 2,000 ft ceiling and 3 miles visibility.
B) If your destination airport has ONLY a GPS approach .
And to file that alternate , - if you're shooting a precision
approach (which requires that you do have the appropriate equipment
in your airplane) .. the forecast weather at the destination has to
be 600 foot ceiling and 2 SM visibility at the ETA (estimated time
of arrival)
- if you're shooting a non precision approach .. the forecast
weather at the destination has to be 800 foot ceiling and 2 SM
visibility at the ETA
- if that airport doesnt even have an instrument approach , the
weather there has to be VFR at the ETA
P.S - a precision approach is an approach that has vertical
guidance , so it makes sense that on precision approaches you have
lower minimums because vertical guidance enables you to get kinda
closer to the ground .