How long can the forecast period be for a TAF issued with "PROB" included?

The correct choice highlights that a TAF issued with "PROB" can indicate a probability of specific weather conditions occurring with a likelihood of up to 30%. In the context of aviation weather forecasting, "PROB" stands for probability, which is used to convey a chance of certain weather phenomena occurring during the forecast period.

When forecasters include a probability forecast, it allows for more nuanced information about potential weather events that may not be as certain as the general forecast. The "up to 30%" designation is important because it provides pilots and air traffic control with critical data on how likely a particular adverse weather condition is to occur, helping them make better-informed decisions.

Understanding this percentage is essential, as it reflects the inherent uncertainty in weather forecasting, especially regarding phenomena that may not be widespread but could still significantly impact flight safety and operations.