Improving Forecasts of Shallow Cumulus for Solar Energy Applications Using Single-Column Modeling and the LASSO Cases

Shallow cumulus cloud fields directly affect the incoming radiation available to solar energy systems. Recent improvements to physics schemes available in the Weather Research and Forecasting model (WRF) aim to improve representation of shallow cumulus, in particular over land. The DOE LES ARM Symbiotic Simulation and Observation Workflow (LASSO) project provides several cases that we use here to test the new physics improvements. The LASSO cases use multiple large-scale forcings to drive Large Eddy Simulations (LES), and the LES output is easily compared to output from WRF single-column simulations driven with the same initial conditions and forcings. The new Mellor-Yamada Nakanishi and Niino (MYNN) Eddy Diffusivity Mass Flux (EDMF) boundary layer and shallow cloud scheme produces clouds with timing, liquid water path, and cloud fraction that agree well with LES over a wide range of those variables. Earlier work is expanded to include cases from 2016; to examine the relative importance of initial conditions, surface fluxes, and advective forcings to the simulations; and to test the coupling between the simulated clouds and the radiation scheme. These tests have informed the current versions of the operational RAP and HRRR models, and new findings will be incoporated into those models.