Which weather phenomenon constitutes a SPECI criterion?

• A. Thunderstorms (Ts) etc.
• B. Light rain only
• C. Mist at low altitude
• D. Clear sky with no cloud

Answer: (A)

A SPECI report is issued when there is a significant weather change between routine observations that could affect aircraft operations. Thunderstorms fit this because they bring hazards like strong winds and gust fronts, severe turbulence, lightning, heavy rain, hail, and even microbursts, all of which can rapidly impact safety and performance. Light rain alone is typically routine and not enough to trigger a SPECI unless it accompanies a rapid, operationally significant change (for example a sudden drop in visibility or a dramatic shift in weather). Mist at low altitude could also be significant if it meaningfully reduces visibility, but it’s the rapid, hazardous impact of thunderstorms that most clearly demands a SPECI. Clear sky with no cloud is normal weather and would not prompt a special report.