Which term in a TAF indicates that conditions are expected to change rapidly?

The term that indicates conditions are expected to change rapidly in a TAF is "TEMPO." This term specifically refers to temporary fluctuations in weather conditions that are anticipated to occur for a short duration, typically lasting from 1 hour to 2 hours. These changes can involve significant shifts in visibility, precipitation, wind, or other weather elements that could impact aviation operations.

For instance, a TAF might include a TEMPO group to signify that within a certain time frame, there is a likelihood of deteriorating weather or a temporary improvement that could affect flight safety.

In contrast, "BECMG" suggests a gradual change in weather conditions over a longer period, which does not align with the idea of rapid changes. The "PROB" term indicates a probability of certain conditions occurring but does not specifically imply a rapid change. "WND" refers to wind and does not indicate a change in weather conditions. Therefore, "TEMPO" is the most suitable term to denote that conditions are expected to change rapidly.