Improvements in Daily Snow-Depth Analysis from Updated Methods and Spatial Statistics

An optimal interpolation method for analyzing global snow depth for Numerical Weather Prediction was developed by Brasnett (1999). A critical part of the method is the use of horizontal and vertical correlation scales to update the analysis each time step. The horizontal e-folding scale is 120 km and the vertical e-folding scale 800m. The method has been shown to give good results for a wide range of snow-depth analysis applications. Since the development of that method, several additional decades of observations have accumulated and it’s possible to updating the correlation model and scales. Here we use data from a densely-sampled region to show that snow-depth analysis can be improved by adjusting the scales and using a different horizontal correlation model.

After showing that spatial correlation models for snow depth can be improved using longer e-folding scales, we tested the impact of the improved correlation models in an analysis of Northern Hemisphere snow depth. Daily 0.25° analysis is performed on snow-depth increments. Snow depth station observations are from the Global Historical Climatology Network. Observed snow-depth increments are computed from NCEP’s Global Forecast System snow depth. Increments are analyzed two ways, one using the Brasnett correlation model, and the other using the updated correlation model. Both analyze a subset of Northern Hemisphere station data, and results are validated against the remaining data. We find that there is minimal difference over the densely-sampled region of the northern US and southern Canada. However, over most of Asia sampling is sparser, and in that region the new correlation model gives consistently higher skill. The improved skill over that region appears to result from the longer horizontal scales in the new correlation model, which make better use of the relatively sparse sampling.

The contents of this presentation are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of NOAA or the U. S. Government.