QPE in the Hydrometeorology Testbed: Methodologies and challenges in complex terrain

NOAA's Hydrometeorology Testbed (HMT) conducts research on precipitation and weather conditions that can lead to flooding and fosters transition of scientific advances and new tools into forecasting operations (hmt.noaa.gov). HMT-West is the first regional demonstration of the HMT project, with emphasis on cold season precipitation in the American River Basin near Sacramento, CA. The suite of instruments deployed in HMT-West include, radars, profilers, disdrometers, and gauges. It is well known that integrating radar and gauges (i.e., multi-sensor information) for quantitative precipitation estimation (QPE) is a challenging problem, even in relatively two-dimensional terrain. This is due to a combination of applied science (i.e., sampling considerations) and basic science (i.e., physical models to represent the drop size distribution) issues. In mountainous regions, the integration of gauge and radar data is especially challenging due to pronounced applied science issues (e.g., radar beam blockage). This paper attempts to quantify the relative importance of the basic and applied science issues in complex terrain, specifically in the context of the HMT-West data set. For example, the relative errors introduced in radar based QPE due to beam blockage, brightband contamination and clutter contamination are evaluated in comparison with the improvement enabled by polarimetric radar estimates and attenuation correction. The basic science and applied science issues are characterized for the HMT west.