The value of portable radars in improving precipitation estimation over complex terrain: Results from the 2005–2006 HydroMet Testbed Project in the American river basin

During the winter of 2006 NOAA's HydroMet Testbed Project deployed a number of sensors to the American River Basin (ARB) in Northern California to test the utility of improving quantitative precipitation estimates (QPE) in rain and snow events. Many rain and snow gages as well as a distrometer for measuring hydrometeor size distributions were placed in the ARB. The winter season of 2005-2006 provided an abundance of heavy precipitation events (water equivalent precipitation exceeded 78 inches from 28 Nov 2005 through 7 March 2006) with which to test the value of transportable Doppler radars in improving QPE in complex terrain region.

This paper will focus on early results of using a portable C-band and polarimetric X-band radars to improve QPE over the ARB. Comparisons of rainfall derived from the radar reflectivity with and without a vertical profile correction (VPR) to raingage observations confirm the poor performance of national S-band network radars in making accurate QPE in the mountainous terrain of the western US, and the value of short-range radars, sited close to the basin, of improving QPE. The sensitivity of the rainfall accumulations to details of the VPR scheme will also be discussed. The distrometer observations are used the “calibrate” the C-band radar to account for biases in reflectivity and specific radar to rainfall relationships, derived by the distrometer, are used for each event to account for possible microphysical differences in the rain or snow production process.