Which precipitation event does not require a SPECI report?

The correct answer is associated with the transition of light snow to heavy snow. In the context of aviation weather reporting, a SPECI report is typically generated to document significant changes in weather conditions that could impact flight safety, such as the onset of precipitation events or significant changes in intensity.

When light snow changes to heavy snow, while it is a notable shift in conditions, it does not necessarily prompt the requirement for a SPECI report. The distinction here is that the condition is still categorized as snow, and the reporting requirements for precipitation types are more focused on the initiation of new forms of precipitation (like freezing rain or ice pellets) or significant changes in the characteristics of already occurring precipitation (like the start of hail).

In contrast, the other options involve significant changes that warrant a SPECI report, as they introduce new types of precipitation or indicate a critical consistency in weather conditions. For aviation purposes, understanding these nuances in reporting helps pilots and air traffic controllers maintain safety during flight operations.