What wind velocity variations would lead to moderately bumpy conditions in flight?

Variations of more than 10 mph in short intervals lead to moderately bumpy conditions during flight because these fluctuations create turbulence that can impact the aircraft's performance and passenger comfort. When wind speed changes rapidly—such as increasing or decreasing by more than 10 mph within a short time frame—it generates irregular airflow around the aircraft. This turbulence can be particularly felt during takeoff and landing phases, where altitude changes and flap configurations might further influence how the aircraft interacts with the shifting wind patterns.

In contrast, calm air with less than 5 mph or consistent winds below 10 mph would generally provide smooth flight conditions because the lack of significant variability in wind velocity allows for stable airflow over the wings. Additionally, stable air could mean less potential for turbulence, whereas merely having more than 10 mph in stable air might not indicate the same bumpy conditions caused by rapid fluctuations. Hence, the correct choice emphasizes the significance of variability in wind speed rather than just the speed itself.