What can indicate severe weather conditions in a METAR report?

In a METAR report, the presence of "TS" (thunderstorm) or "WS" (wind shear) codes signifies conditions that can indicate severe weather. Thunderstorms are often associated with intense precipitation, strong winds, and electrical activity, which can lead to hazardous conditions both on the ground and in the air. Wind shear refers to abrupt changes in wind speed and direction, which can be particularly dangerous for aircraft during takeoff and landing, contributing to turbulence and potential loss of control.

The other options do not typically indicate severe weather on their own. For example, "FS" codes referring to fog and smog can certainly affect visibility but are not as directly indicative of severe weather as thunderstorms. "TZ" codes for the tropical zone also do not specifically relate to severe weather conditions, as they instead provide information about the region's climatic classification. General weather patterns over several days may suggest trends or eventual severe weather but are not specific indicators in a single METAR report. Thus, the presence of "TS" and "WS" codes is the most direct indication of severe weather conditions.