The Initialization of the Divergent Component of the Horizontal Wind in Mesoscale Numerical Weather Prediction Models and Its Effect on Initial Precipitation Rates.

Numerical weather prediction models have not produced accurate precipitation forecasts, especially short-term forecasts of significant precipitation events. One reason for this has been that numerical models are normally initialized with nondivergent winds. This means the model must develop a vertical motion field and an associated precipitation field. Therefore, the initial precipitation rate is underforecast and the precipitation forecast itself is adversely affected. One method of solving this problem is the initialization of the divergent wind component hereafter termed divergent initialization. The general divergent initialization procedure proceeds as follows omega values are diagnosed using the omega equation velocity potentials are derived from the vertical velocities with the continuity equation the divergent wind components are obtained from the velocity potentials geopotentials are calculated on sigma surfaces using a balance equation with contributions from both the nondivergent and divergent wind components finally, balanced temperatures are derived using the hydrostatic equation.