Orographic precipitation: Rapid advancements through recent field studies, continuous measurements, and modeling

Orographic precipitation depends on a number of complex dynamical and microphysical processes, which have been explored recently using field studies, such as MAP over the Alps, CALJET over coastal southern California, IPEX over the Wasatch Mountains of Utah, and IMPROVE2 over the Oregon Cascades. This talk will discuss how these field observations combined with mesoscale modeling have led to several new advances in our understanding orographic precipitation processes. Particular emphasis will be placed on how mountain gravity waves can impact the precipitation distribution, efficiency, and microphysics for large barriers as well as even for small coastal hills. Although mesoscale models run at ~1-km grid spacing have been shown to realistically simulate the precipitation distribution associated various moist dynamical processes over complex terrain (e.g., flow blocking, mountain waves over ridges, etc), large uncertainties and errors still exist in the model microphysics when simulating orographic clouds. Fundamental questions involving moisture loss and transport for air parcels crossing complex terrain areas also exist.

In addition to field studies, continuous in situ measurements are necessary to better understand the climatology of different precipitation modes over terrain as well as steady versus intermittent precipitation processes. It will be shown how even conventional datasets, such as the WSR-88D, as well as other long-term microphysical measurements at the surface, are helping to bridge the gap between recent field studies and the full spectrum of orographic precipitation responses.