A diagnostic method for high-resolution precipitation prediction using dynamically adapted vertical velocities

Summary

A method for diagnosing precipitation intensity based on a high-resolution vertical motion field is proposed. Vertical motion at a high resolution is obtained by a short dynamic adaptation integration of the fine-mesh model, which follows the interpolation of the model fields from the lower resolution model onto the finer mesh with better description of the relief. As precipitation depends directly on the vertical velocity, knowing the vertical velocity field makes the diagnosis of the precipitation intensity possible and rather successful in cases when regional differences in precipitation are mainly caused by blocking and channeling due to smaller scale relief characteristics. The diagnosis can be done in 3 different ways: statistically, by adiabatic adjustment, or by using the 1D model. Results of applying the method are presented for the MAP IOP-10 case (Mesoscale Alpine Project – Intensive Observational Period 10), when maximum intensities of up to 35 mm/h have been observed in the Julian Alps region of the western Slovenia, at the end of this IOP on October 25th, 1999. The method performed well and the maximum diagnosed intensities based on 2.5 km horizontal mesh dynamically adapted vertical motion field surpassed 30 mm/h. This corresponds to the observed intensities at several rain gauges in the area.