NOAA’s National Snowfall Analysis: Technical Description and Evaluation

In 2014 the National Weather Service (NWS) identified the need for a single, authoritative, CONUS-wide gridded analysis of snowfall for forecast verification, decision support, and general public use. In 2017 the NWS Office of Water Prediction released an online, downloadable prototype analysis that fulfills this need. The process of deploying this analysis onto a permanent operational platform has begun.

The National Snowfall Analysis version 2.1 (SFAv2) synthesizes several NWS data sources to produce a unified CONUS-wide gridded snowfall analysis. These sources include the Stage IV mosaic of quantitative precipitation estimates (QPE) generated operationally at NWS River Forecast Centers, precipitation type estimates from short-term numerical weather prediction (NWP) model forecasts, and climatological snowfall-to-liquid ratio (SLR) estimates generated from the Global Historical Climate Network (GHCN) dataset. The analysis reconciles these products with real-time snowfall observations from NWS Cooperative observers, NWS spotters, CoCoRaHS observers, and other observing networks.

The National Snowfall Analysis combines an unbiased background, or first guess, with a two-pass ordinary kriging (OK) process that is parameterized based upon the real-time spatial correlation among differences between observed and background snowfall. Version 2.1 was placed into production for the 2018-2019 winter season. It is accompanied by a ten-year (October 2009-September 2018) retrospective analysis, and the combined 11-year dataset constitutes the first period of record with which future analyses can be compared.

This presentation will describe the SFAv2 process in greater detail, will discuss the performance of the analysis using a variety of statistical techniques, and will recommend improvements that may be pursued in future development cycles.