What weather phenomenon is often associated with jet streams?

The correct answer is clear air turbulence, which is frequently associated with jet streams due to the significant changes in wind speed and direction that occur at these altitudes. Jet streams are fast-flowing air currents high in the atmosphere that can create sharp boundaries where air masses of differing temperatures and speeds meet. These boundaries can lead to turbulence, particularly in clear air where visual indicators of rough weather, like clouds, may not be present. Pilots need to be aware of the locations of jet streams, as the turbulence can be sudden and intense, impacting flight safety and comfort.

The other weather phenomena mentioned, such as thunderstorms, hail storms, and fog, are generally linked to different meteorological conditions. Thunderstorms typically develop in environments where there is abundant moisture and instability in the lower atmosphere, rather than at the high altitudes where jet streams reside. Hail storms also require specific conditions such as strong updrafts, which are more characteristic of thunderstorm development. Fog typically forms at ground level when there is cooling and moist air, rather than in the upper atmosphere where jet streams exist. Therefore, clear air turbulence is the most directly related phenomenon to jet streams, making it the correct choice.