Using topography and synoptic categories to improve climate mapping

The National Climatic Data Center is developing a method to calculate high-resolution gridded climatologies (approximately 5 km) using daily station measurements, Numerical Weather Prediction retrospective analyses, and high resolution topography grids. The method is known as the ‘Two Component Synoptic Region' (TCSR) model, because it uses the sum of a topographic component and a non-topographic component to estimate daily meteorological values on a high-resolution grid. The topographic component groups daily station data into “synoptic regions” and uses a statistical model that relates the quantity to be mapped to elevation and to the angle the low level wind makes with the gradient of elevation. Synoptic regions are moving, contiguous collections of grid cells that exhibit a common synoptic property, i.e., synoptic regions are based on synoptic weather types. The non-topographic residual component is estimated from an inverse distance spatial distribution model that accounts for clustering. Climatologies are computed by averaging the resulting long series of daily grids over time to obtain Julian day average grids and monthly average grids.