The West Coast Picket Fence Experiment during STORM-FEST

Abstract

Mesoscale weather systems that develop in the central United States are often forced by environmental features that have formed far upstream over the conventional data-sparse Pacific Ocean. Although remotely sensed observations, such as satellite retrievals, are becoming more numerous and accurate, they still may not have the resolution necessary to enhance global model-based analyses and forecasts over this region. These global model products are the primary source of lateral boundary conditions that have been found to have large impacts on the downstream forecast skill of regional mesoscale models over the United States. in addition, the temporal and spatial resolution of the current rawinsonde network along the West Coast may not be sufficient to detect and measure mososcale flow features as they move inland. During the STORM-FEST experiment in February-March 1992, a ?Picket Fence? of seven special rawinsonde stations were interspersed among the seven regular rawinsonde sites from Port Hardy, British Columbia, to Sap Diego, California. All sites obtained observations every 3 h rather than the normal 12 h. The objective of the Picket Fence was to examine the feasibility of using extra observations in time and space to improve upstream boundary conditions for forecasts of mesoscale weather events in the central United States. As a first step in examining the potential boundary condition impact of the Picket Fence, fluxes of mass, beat, momentum, potential energy, kinetic energy, and moisture across the West Coast resolved with various spatial and temporal combinations of Picket Fence data are compared with the 12-h regular upper-air sites as the standard. When a wave system crossed the middle of the Picket Fence, significantly different fluxes were calculated with the full spatial and 3-h Picket Fence observations. For other systems that crossed near the margins of the Picket Fence, only small changes were detected by the additional observations.