When is the FROM (FM) group used in a TAF?

The FROM (FM) group in a TAF, or Terminal Aerodrome Forecast, is specifically utilized when there is an expected rapid change in prevailing weather conditions. This indicates that significant changes are anticipated within a short time frame, often associated with the arrival of a front or a similar weather system. The FM group helps pilots by providing timely and critical information about these abrupt shifts, enabling them to adjust their flight plans and operations accordingly.

In contrast, the other options do not correctly describe the purpose of the FROM group. For instance, stable weather conditions do not necessitate a rapid change indication, and minor modifications in wind speed would not be significant enough to warrant a dedicated FM group. Finally, while the FM group can indicate a change expected to last more than three hours, its primary focus is on the immediacy and rapidity of the change rather than its duration. Thus, the correct use of the FM group is vital for understanding and reacting to fast-changing weather patterns.