Exploring How Urban Heat Islands Can Affect Winter Precipitation Type in Support of UAS/UAM

The rising interest in UAM and UAS operations in cities is motivating new efforts to provide regulations and meaningful decision support guidance for when/where these aircraft can fly. Most efforts to date on this subject focus on wind patterns in urban areas. But another key limiter to UAS operations is winter precipitation type, which is very poorly understood for the surface layer over urban areas. A few studies have shown bulk statistical evidence of this phenomena using ASOS weather type data. But little work has been done to characterize this with case studies. This talk will outline the observational problems associated with this phenomena and introduce a case study that illustrates how mixed-phase precipitation in concert with an urban heat island (UHI) can impact UAS/UAM operations.

For this study, 6 years of ASOS data was collected and analyzed for 14 cities in the USA. In bulk statistics, an urban heat island (UHI) signal was found in the ASOS precipitation-type data, but this signal was highly dependent on the choice of thresholds (temperature and wind) employed and the definition for declaring an ASOS station as “urban” or “non-urban”. An event-based approach was also employed by analyzing simultaneous precipitation-type reports from ASOS stations in and around an urban area. This analysis was done to identify case studies for a more in-depth understanding of this phenomena. An analysis of a freezing rain case study in Dallas/Fort Worth, TX will be shown and illustrates the importance of having a 3D characterization of hydrometeor phase for these events to inform UAS/UAM operations.