High-Wind Alerts for the Purdue University Campus Based on Observations from the X-Band Teaching and Research Radar (XTRRA)

Following the 13 August 2011 Indiana State Fair stage collapse tragedy, which was caused by a wind gust from an approaching thunderstorm, Purdue University in northwest Indiana enforced a wind speed restriction of 30 mph (13 m s^-1) for tents at outdoor events. During these events, volunteers stand outside with handheld anemometers, measuring and reporting when the wind speeds exceed the limit. In this study, we report testing of a new system to automate high wind alerts based on observations by a Doppler radar near Purdue campus (the XTRRA). The XTRRA scans the atmosphere at low elevations over campus approximately every five minutes. Using XTRRA data collected over its first eight months of operation, we developed an algorithm that generates high wind alerts whenever observed winds at altitudes below 240 m (the height of the football stadium) exceed the threshold of 13 m s^-1. We describe how a combination of median filtering, clutter filtering, and statistical outlier removal mitigated false alarms caused by noise and ground clutter. The automated high wind alerts are validated against wind gust observations from a nearby ASOS (KLAF). It is found that the alerts work well in high wind events associated with precipitation, but less well in high wind events that are not associated with precipitation (e.g., frontal passages). This is likely because the XTRRA, which has a wavelength of 3 cm, is less sensitive to clear-air echoes than an operational WSR-88D. Following further testing, we envision that these automated high wind alerts will be distributed to interested parties such as campus event coordinators and safety officials.