Using WRF to Determine the Effects of Natural Sensitivities on Orographic Precipitation

Orographic precipitation is an important source of water for parts of the world. However, many factors affecting orographic precipitation are not well understood. This study uses modeling to investigate natural sensitivities of orographic precipitation in producing snow and in its spatial distribution. Based on observations from Seeded and Natural Orographic Wintertime clouds: The Idaho Experiment (SNOWIE), several variations of a 2-D idealized hill case were run using the Weather, Research, and Forecasting model V4.1 (WRF) in order to investigate snow precipitation. The idealized case used a simple terrain and an idealized temperature profile based on SNOWIE observations as realistic set-up for orographic precipitation. A series of wind and temperature profile variations were run to study the sensitivity of the spatial and temporal distribution of orographic snow. We found that the model was very sensitive to small changes in wind and temperature, with the largest amounts of snow being generated using the initial temperature profile. Increases in wind speed increased the amount of windward generated snow. Temperature increases and decreases of up to 3 K reduced both the windward and the leeward snowfall. Temperature has a large effect on cloud liquid water and ice content needed for producing snowfall in the model.