Final answer:
The alternate weather minima requirement for non-precision approach facilities providing straight-in minima to separate suitable runways is 800-2 or 300-1 above the lowest usable HAT/HAA and visibility, whichever is greater. They ensure that an alternate airport is suitable for landing despite adverse weather conditions.
Step-by-step explanation:
For facilities with non-precision approaches available and when they provide straight-in minima to separate suitable runways, the alternate airport weather minima requirements is: 800-2 or 300-1 above the lowest usable Height Above Touchdown (HAT) or Height Above Airport (HAA) and visibility, whichever is greater. This means that an alternate airport must have forecasted weather conditions at least 800 feet above the lowest HAT/HAA, with a minimum visibility of 2 miles, or 300 feet above the lowest HAT/HAA and a visibility of 1 mile, depending on which set of conditions provide a higher minimum.
It is essential to consider these minima when planning for alternate airports in case the intended destination airport becomes unusable due to weather conditions such as clouds, wind, and rain. Pilots and dispatchers use these criteria to ensure that there is a suitable backup plan that allows for a safe landing in case the primary airport is not an option.