What disqualifies an airport from being used as an alternate?

An airport is disqualified from being used as an alternate if the forecasted weather includes conditions that do not meet the minimum requirements for alternate airports. Specifically, if the weather forecast indicates that the visibility or cloud cover is below the required minima for an alternate airport, it cannot be classified as suitable for use.

In this case, the presence of rain showers in the forecast could lead to reduced visibility and potentially low ceilings, which might not meet the established criteria for alternate airport status. Therefore, the forecast of adverse weather is a key factor in determining the usability of an airport as an alternate.

The other options do not inherently disqualify an airport. Having multiple compatible approaches might actually enhance the airport's usability as an alternate, while requiring monitored NAVAIDs indicates the need for specific navigational aids but does not rule it out. Scheduled commercial flights may suggest operational capacity but do not directly affect the alternate status based on weather criteria.