What weather condition is associated with 'TS' in METAR?

The designation 'TS' in a METAR report stands for "thunderstorm." This abbreviation is used to indicate the presence of thunderstorm activity at the time of observation. Thunderstorms can be significant indicators of severe weather since they often accompany heavy rain, lightning, hail, and even tornadoes. Therefore, when you see 'TS' in a METAR, it signifies that pilots and meteorologists should expect turbulent and potentially hazardous conditions due to the storm's activity.

The other options refer to different weather phenomena: 'freezing rain' involves rain that freezes upon contact, creating hazardous conditions; 'fog' indicates reduced visibility due to water vapor; and 'haze' refers to a slight obscuration of the atmosphere caused by water droplets or particles. Each of these conditions has its unique abbreviations in METARs, but 'TS' specifically highlights the presence of thunderstorms.