Question: Does an automated surface observation system (ASOS) have a built-in lightning detection system? Without an observer, how does it know to add a thunderstorm (TS), thunderstorms in the vicinity (VCTS), or tell you about lightning in the distance?
Answer: Some ASOS sites do have a single-site lightning sensor in the array. If there isn’t a lightning sensor at the site, it is still possible for the ASOS to report lightning. For FAA-sponsored ASOS sites without a lightning sensor, lightning data is made available to the ASOS through the automated lightning detection and ranging system (ALDARS), which is a ground-based lightning detection system. ALDARS is not coresident with the sensor and sends the data to the ASOS. Here’s how it all works at a simplified level.
Without a human observer logged in to the ASOS terminal, it will format a METAR or SPECI (special observation) for lightning in one of three ways: TS, VCTS, or lightning in the distance.
