Forecast Of Low Clouds Over A Snow Surface In The Arctic Using The Wrf Model

The Swedish Armed Forces configuration of the Weather Research and Forecasting (WRF) Model has problems in forecasting low clouds in stably stratified conditions when the ground is covered by snow. Reforecasts for January and February 2018, together with observations from Sodankyla in northern Finland, are analyzed to find the cause. The investigation is done iteratively between the single-column model (SCM), applied at Sodankyla, and the full 3D version. Our experiments show that the forecast error arises due to inadequate initialization of stratocumulus (Sc) clouds in WRF using the ECMWF global model, Integrated Forecasting System (IFS). By including bulk liquid water and bulk ice water content, from IFS in the initial profile, the downwelling longwave radiation increases and prevents the near-surface temperature from dropping abnormally. This, in turn, prevents artificial clouds from forming at the first model level. When no clouds are present in the IFS initial profile, the Sc clouds can be initialized using information from the observed vertical profiles. Generally, initialization of Sc clouds in WRF improves the forecast substantially.