During PACJET 2001, an intense extratropical cyclone developed rapidly off the Southern California coast and produced substantial rainfall as it interacted with coastal topography. Operational models tended to misplace the position and underforecast the intensity of the storm, which was due in part to a lack of observations over the cyclogenesis region off the coast of Southern California. PACJET made dropsonde and other insitu observations in the area, which were available for data assimilation tests using the Navy's COAMPS model. NPS has developed both two- and three- dimensional multiquadric based data assimilation for COAMPS and other models and we can run the multivariate optimum interpolation (MVOI) with COAMPS, as well.

Previous work has suggested that orographic rainfall predictions by a mesoscale model are sensitive to details in the specification of initial conditions. In this talk, the sensitivity of the cyclogenesis and subsequent orographic rainfall to the choice of data assimilation method will be examined. The range of forecast errors and character of the forecast differences will be examined to highlight crucial aspects in the initial state that must be faithfully represented by the assimilation system to accurately predict the cyclogenesis and orographic rainfall.