Which of the following does NOT meet SPECI criteria?

The correct answer is that surface visibility remains constant, as this does not meet SPECI criteria. The SPECI (Special Weather Report) criteria establishes conditions that warrant an update to routine METAR observations. These criteria aim to provide pilots and meteorologists with timely information on significant changes in weather conditions.

In the context of this question, when surface visibility remains constant, it indicates that there has been no significant change in the visibility conditions; therefore, it does not warrant a special report. On the other hand, the other options relate to significant changes in weather conditions. Notably, significant changes in wind direction, the onset of precipitation, and substantial variations in cloud cover are all critical factors for pilots that can affect flight safety. When these events occur, they imply a notable variation in the weather, prompting the need for updated meteorological information.

Thus, a scenario where visibility stays the same does not indicate any significant weather development necessary for a SPECI report.