Which visual indicator can sometimes be seen during flight associated with the jet stream?

The presence of long streaks of cirrus cloud is often associated with the jet stream, which is a fast-flowing ribbon of air high in the atmosphere. These cirrus clouds form as a result of the large-scale atmospheric disturbances caused by the jet stream's influence. The jet stream can alter weather patterns and lead to the development of high-altitude clouds, primarily cirrus types, which appear as thin, wispy streaks.

The formation of these clouds occurs as moist air is lifted by the jet stream, causing ice crystals to condense and form clouds at high altitudes. Additionally, the orientation and appearance of cirrus clouds can provide important information regarding the wind direction and speed aloft, which are critical for understanding weather systems.

In contrast, fluffy cumulus clouds are typically associated with convective activity and are not directly related to the jet stream. Dense fog is a ground-level phenomenon resulting from high humidity and cooling but does not have a relationship with high-altitude jet stream activity. Thunderstorm cells are associated with significant atmospheric instability and moisture but are not direct indicators of the jet stream itself. They occur independently of the jet stream's positioning.