The network of NWS Doppler radars (WSR-88D) was designed in part to provide quantitative estimates of precipitation (Crum and Alberty 1993; Klazura and Imy 1993). Numerous studies focusing on precipitation in the eastern half of the U.S. have been undertaken to test and evaluate the algorithms used to make these estimates (e.g., Fulton et al. 1998; Anagnostou and Krajewski 1998; Baeck and Smith 1998; Fo et al. 1998). Only recently have similar efforts been attempted in the complex terrain of the Intermountain West, where the use of these algorithms has not been optimized (Vasiloff 1997; Cairns et al. 1998).

Precipitation formation and distribution processes in the complex terrain of the Intermountain West are not well understood, one of the primary motivating factors for conducting IPEX. This uncertainty impacts the relationship between radar reflectivity (Z) and precipitation rate (R), a critical component of the WSR-88D precipitation algorithm. The Z-R relationship is dependent upon the ice habit and how the concentration of precipitation particles is distributed in size. IPEX datasets will be used to examine these parameters and how they vary in time and space.

Most WSR-88D's in the Intermountain West, such as the one located nearest Salt Lake City (KMTX), are located at relatively high elevations to limit beam occultation and thus enable broad regional coverage. However, an undesirable side-effect of this siting strategy is that, in relatively shallow orographic precipitation, most of the cloud is below the lowest elevation scan of the WSR-88D (i.e., 0.5 degrees). This problem, exacerbated at increasing radar ranges by the curvature of the earth, often causes underestimates of precipitation rate at the surface. These underestimates result from an inadequate knowledge of precipitation processes occurring between the levels sampled by the WSR-88D and the surface. Microphysical datasets collected during IPEX will be used in combination with a detailed microphysical model (Mitchell 1988,1996; Lawson et al. 1998) to better understand the precipitation processes occurring in this layer. A deep vertical layer between the WSR-88D scanning domain and the surface also complicates evaluations of algorithm performance due to horizontal advection of precipitation particles. Kinematic datasets collected during IPEX will be used to make more robust precipitation algorithm evaluations.