Assessing the Influence of Topography on Convective Storm Environments Using High-Resolution Operational Model Output

The effects of topography on convective storm environments are difficult to observe, owing to the spatial resolution of the observations required.  NCEP’s High-Resolution Rapid Refresh (HRRR) is able to resolve at least some of the influences of topography, however, owing to its relatively fine horizontal grid spacing (3 km)  Short-range forecasts (2-h) from the HRRR are used to develop climatologies of commonly used convective storm forecasting parameters, such as CAPE, SRH, and STP.   The climatologies are used to diagnose where convective parameters are systematically perturbed relative to topographic features.  The parameter fields are averaged on days supportive of convective storms.  Averaging many different “convective days” greatly diminishes synoptic- and mesoscale variability, thereby exposing topographic signals (variability resulting from the background hemispheric-scale temperature/pressure gradient also is evident in the mean fields).   We examine the influence of topography in four different regions of the United States: the Northeast, Southeast, southern Great Plains, and northern Great Plains.

The mean fields of convective forecasting parameters exhibit considerable heterogeneity in the eastern United States, much of which can be attributed to mountains, valleys, and coastlines.  The anomalies are sensitive to ambient low-level wind direction (i.e. where winds locally blow upslope or downslope), especially for parameters dependent on low-level vertical shear.  In general, less heterogeneity is present on the Great Plains; however, notable exceptions exist, such as within and near the Black Hills (South Dakota), and along the Caprock Escarpment (Texas).