Eliminating Excessive Evaporation by Reducing Explicit Drop Break-Up Due to Collisions with Graupel in RRFS

Large supersaturations with respect to water were found in 3-km Rapid Refresh Forecast System (RRFS) runs of a warm season case using the Thompson microphysics. It was determined that rain evaporation was producing a temperature tendency near 27C/hour due to the presence of many tiny drops. The tiny drops were the result of graupel and rain collisions (from melting graupel). Sensitivity tests were made reducing the number of drops produced from the graupel-rain collisions, and a solution was found to reduce the supersaturations to less than 3%. Verification was run on a total of ten cases (5 warm season, 5 cool season) in order to assess the impact. A slight increase in heavy precipitation biases, and a decrease in a 2m temperature bias were noted. Verification stats as well as 2D maps and vertical cross sections of processes will be shown for one warm season case.