13.3 Forecasting downslope wind storms and spillover precipitation at the Reno, NV National Weather Service forecast office

Thursday, 2 September 2010: 2:00 PM
Alpine Ballroom A (Resort at Squaw Creek)
Rhett Milne, NOAA/NWSFO, Reno, NV; and C. Smallcomb and J. Wallmann

The NOAA National Weather Service forecast office in Reno, NV issues official forecasts and warnings for a diverse geographical area covering the Sierra Nevada Mountains and western Nevada. A significant portion of the population within that district is located in the cities of Reno and Carson City, NV, which are prone to downslope wind storms that have resulted in damage and major travel impacts. The other primary forecast challenge during winter storms is how much of the precipitation will make it past the Sierra crest into leeside valleys, known locally as spillover. When accompanied by high snow levels and snow melt, heavier spillover precipitation events have lead to historic flooding events along the Truckee and Carson Rivers, such as in 1997 and 2005.

This presentation will exhibit techniques forecasters at NWS Reno use to predict downslope wind storms and spillover precipitation in the lee of the Sierra. These take advantage of both deterministic and ensemble model forecasts, along with and observational data. Several recent case studies will be used to demonstrate. Forecasters make use of: 1) conceptual models of jet streak and mid-level front positions, mountain top wind speeds, and stability and moisture profiles to examine NCEP model forecasts via plane view maps and spatial height cross-sections, 2) a locally developed program based on climatology of downslope wind events, 3) ensemble plume diagrams of key ingredients from the NCEP SREF ensemble model and normalized anomalies from the NCEP GEFS model, 4) high resolution modeling, including a local on-demand WRF, and 5) real-time observations from the HMT-West project. Many of these techniques have been the result of research by NWS Reno forecasters and collaborative projects with the Desert Research Institute.

We seek not only to showcase our techniques, but also to receive feedback from experts attending the conference on areas where improvement can be made in downslope wind and spillover forecasts. Ultimately we want to cultivate enhanced partnerships with the research community to help improve these forecasts.

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