An additional alternate will be designated anytime when?

An additional alternate should be designated whenever there are poor weather conditions or when the flight encounters turbulence. This is rooted in safety regulations and best practices in flight operations. Poor weather conditions can significantly impact landing options, as they may reduce visibility or create unsafe landing scenarios at the intended airport. Similarly, turbulence may affect the aircraft's handling and require the crew to adapt their flight planning, which could necessitate having backup landing options readily available. By designating an additional alternate in these circumstances, flight crews ensure that they maintain a high standard of safety by preparing for unexpected changes in flight conditions that could necessitate a diversion. This proactive approach is crucial in aviation to mitigate risks and ensure the safety of passengers and crew.