Diurnal variation of precipitation over the Carolina Sandhills region

The Carolina Sandhills are known to have an area of maximum precipitation on its western boundary during the summer mainly due to differences in soil types. Statistical analysis was performed on summer precipitation data from automated weather stations in the Carolinas, along the Sandhills for the years 2001 to 2006. Statistically significant difference was observed between the day and night precipitation amounts. A case study also revealed the diurnal pattern of convective precipitation. North American Mesoscale (NAM) model forecasts for the summers of 2004 to 2006 were evaluated using observations. The model underpredicted precipitation significantly during nights. A numerical simulation using Weather Research and Forecast (WRF) model was performed for August 9-11, 2001 and the forecasts were compared with observed precipitation data. The model precipitation forecasts were better for daytime as compared to the night. This feature is attributed to model physics not capturing cloud-radiation interaction processes dominant during nights. Although this study is for a specific region in the US, results are applicable for other regions for similar conditions.