The Challenges of Light Precipitation and Its Radar Display

It is important for radar displays to correctly to show meteorological echo while hiding nonmeteorological echo. Failure on either of these objectives presents users with an unrealistic display of ongoing precipitation, creating difficulty for those making weather-related decisions. Two factors that can influence what is seen on a radar display are quality control and volume coverage pattern (VCP) mode. This presentation highlights the challenges with displaying light precipitation and offers the beginning of solutions.

Quality control algorithms must be able to identify nonmeteorological echo so that it may be removed. A challenge, however, is that light precipitation echo (e.g., light rain, light snow, and drizzle) oftentimes has similar single and dual-pol characteristics as nonmeteorological echo. Automated Surface Observing System (ASOS) clear sky conditions and reported precipitation are used to divide one year of WSR-88D radar data across the continental United States into meteorological and nonmeteorological categories. The single and dual-pol characteristics of both meteorological and nonmeteorological echoes are used to identify discriminatory signatures. It is found that using multiple single and dual-pol fields offers improved distinction between light precipitation and nonmeteorological echo.

VCP mode may also affect the ability to display light precipitation. Long radar pulses increase the radar’s ability to detect light precipitation, but decrease the range resolution. VCP 31 uses a long pulse while other VCP modes use a short pulse. It has been observed that as VCP mode changes from long pulse to short pulse, some light precipitation echoes vanish from the radar display. Using one year of ASOS present weather reports and the Multi-Radar Multi-Sensor (MRMS) radar display, the degree and frequency of short pulse VCP modes failing to detect light precipitation is investigated.