Which of the following is a limitation of MOS forecasts?

The correct choice emphasizes a significant limitation of MOS (Model Output Statistics) forecasts, which relates to their applicability for alternate airport filing. MOS forecasts are primarily designed to provide short-term and specific weather predictions, which may not fully encompass the variations or uncertainties that can arise with adverse weather conditions at alternate airports. This makes MOS forecasts less reliable when a pilot needs to designate an alternate airport, as the forecasts may not adequately reflect longer-term weather trends or significant changes that can occur over time.

For the other options, they do not convey accurate limitations of MOS forecasts. The complexity of the forecasts can vary depending on the user's familiarity with interpreting them, and while some pilots find them complex, they are generally accessible for those trained in meteorology. Additionally, while MOS forecasts do cover shorter time frames, this aspect alone does not directly correlate with their suitability for alternate airport filing. Lastly, stating that they do not provide any valuable data is misleading, as MOS forecasts do deliver important insights regarding short-term weather patterns that can be invaluable for pre-flight planning and safety assessments.