Numerical forecasting of winter coastal storms during CASP: Evaluation of the regional finite‐element model

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Abstract
As part of the Canadian Atlantic Storms Program (CASP), a meso‐α scale version of the regional finite‐element model was set up for the short‐term forecasting of East Coast storms during the CASP field phase. The main features of the mesoscale model compared with the operational continental version include a 100‐km resolution over a reduced domain, a modified physics package, improved surface and geophysical field analyses, and the refinement of initial moisture analyses using satellite imagery. Field evaluations of the mesoscale and continental models by CASP meteorologists indicated that both models generally underpredicted storm speed and deepening and that the CASP model yielded more accurate storm locations. Mesoscale forecasts of precipitation types and boundary‐layer winds were quite realistic when compared with actual station reports. Objective verification scores for 11 storm cases confirm the better meteorological performance of the mesoscale model. The most striking improvements are found at 300 mb for the geopotential height and near the surface for the temperature. The structure of the forecast errors suggests that high horizontal resolution and a better convection scheme are important for the simulation of the upper‐level trough, while a more realistic sea surface temperature analysis improves the storm evolution at lower levels. Enhancement of initial moisture analysis using satellite imagery generally increases precipitation amounts in the early hours of the forecast but has little impact later on.