Study of the nature and frequency of ASOS thunderstorm (TS) and vicinity thunderstorm (VCTS) reports in METARs

The purpose of this research is to evaluate the nature and frequency of thunderstorm (TS) and vicinity thunderstorm (VCTS) reports in metar reports from commercial airports in the contiguous United States. To evaluate truthfulness of TS and VCTS reports, 5-minute ASOS observations from all commercial airports in the contiguous United States from calendar years 2016 through 2023 were evaluated as well as the number and frequency of TS and VCTS reports. These were compared to independent observations of lightning from Earth Networks Inc (ENI) and to the National Lightning Detection Network (NLDN) in order to analyze the relation between lightning detection and TS and VCTS instances.

Moreover, some reports are made automatically and go through the algorithm, and some reports are made by humans. So, it is important to know if the algorithm is reporting correctly TS and VCTS, if human reports are correct and to what extent they increase or decrease the variability in TS and VCTS reports. We found that at airports that have more frequent human augmentation of the observations, that there are more TS reports than VCTS reports. This result does not meet expectations because the VCTS area is three times larger than the TS area. Thus, humans seem to overreport TS instead of VCTS. The tendency for human observers to overreport TS at the expense of VCTS could impact airlines by pushing a pilot to divert the flight and create some extra cost for the airline. On the other hand, the lightning-based algorithm seems to report more VCTS than TS in smaller airports, but if the algorithm is underreporting TS and/or VCTS, it could create some safety issues for planes and passengers. To finish, two study cases have been chosen to shine a light on the relation between automated lightning detection and ASOS reports of TS and VCTS.