Improving Weather Research and Forecasting Model Initial Conditions via Surface Pressure Analysis

A preprocessor (Obsgrid) that creates input data for the Advanced Research version of the Weather Research and Forecasting model (WRF-ARW) is modified to perform a surface pressure objective analysis to allow surface analyses of other fields to be more fully utilized in the WRF-ARW initial conditions. Nested 27-, 9-, 3-, and 1-km horizontal grid spacing domains centered over San Francisco, California, on 9 February 2012 reveal an area in the initial condition surface fields of the 1-km domain in which horizontal gradients are very small, with sharp gradients at its edges. The lack of an objective analysis of surface pressure unnecessarily limits the application of other surface analyses into the WRF initial conditions and contributes to the creation of these structures. Therefore, a surface pressure objective analysis was added to Obsgrid for 9 February and also 4 additional case days. The surface pressure objective analysis allows surface analyses of other fields to be more fully utilized in the WRF initial conditions and leads to improvements in model air temperature and especially dewpoint. However, these improvements are not seen in observation nudging experiments since the observation nudging corrects for the errors introduced by the original lack of surface pressure objective analyses. The original document contains color images.