Final answer:
The minimum weather criteria required to designate an airport as an alternate involve the concepts of 'ceiling' and 'visibility', which refer to cloud cover height and visibility distance. These criteria vary depending on the aircraft type and airport approach procedures.
Step-by-step explanation:
In aviation, the minimum weather conditions required to designate an airport as an alternate are known as minimum weather criteria. These criteria include the concepts of 'ceiling' and 'visibility', which refer to the height of the lowest cloud cover and the distance a pilot can see, respectively.
The specific minimums for ceiling and visibility vary depending on the type of aircraft and the airport's approach and landing procedures. For example, an alternate airport for a commercial jet may require a minimum ceiling of 1000 feet and a visibility of 3 miles.
It is important to note that these criteria ensure safe operations and provide pilots with a backup option in case the primary airport is not accessible due to adverse weather conditions.