Which weather phenomenon consistently occurs when flying across a front?

When flying across a front, a change in wind direction is a consistently observed phenomenon. This occurs due to the distinct temperature and pressure differences that characterize fronts. As an aircraft crosses a front, it moves from one air mass into another, which is often associated with varying wind patterns.

The frontal boundary typically represents a significant transition in meteorological conditions, where the characteristics of the air masses on either side differ markedly. For instance, a cold front may bring winds from the northwest into an area where warm, southerly winds had previously been dominant. This wind shift can lead to turbulence and changes in flight conditions, making it a reliable indicator of crossing a front.

While changes in temperature, atmospheric pressure, and visibility might also occur when crossing a front, they are not as consistently linked to the act of crossing the front as a change in wind direction. Temperature changes will certainly happen but can vary in intensity, and pressure adjustments are often gradual over a larger area rather than an instantaneous shift. Visibility, likewise, can be affected by various factors and is less predictable than the wind direction changes that accompany a frontal passage. Therefore, the most reliable and consistent weather phenomenon when flying across a front is indeed a change in wind direction.