What can a TAF include that indicates conditions with a chance of occurrence?

The correct answer is based on the fact that the TAF (Terminal Aerodrome Forecast) uses the term "PROB" to indicate a probability of certain weather conditions occurring within a specified time frame. When "PROB" is used in the context of a TAF, it is followed by a percentage and describes a likelihood—usually in percentages—of a forecasted condition occurring. For example, a TAF might state “PROB30” indicating a 30% chance of certain weather happening.

The other options do have their own roles in the TAF but do not serve to communicate the probability of occurrence. "From" and "To" are used to define the time range for which specific weather conditions are being forecasted, rather than indicating the likelihood of those conditions. Therefore, "PROB" is unique in its function to convey the chance of occurrence of certain weather conditions, making it the correct answer to the question.