National Snowfall Analysis Version 2

The NWS’s Office of Water Prediction (OWP) produces high-value snowfall information for water supply and flood risk planning. The development of an improved snowfall analysis will benefit the NWS Winter Weather Program by providing critical real-time feedback for verification purposes and longer-term verification of human and NWP snowfall forecasts. The analysis will also facilitate decision support activities for core partners, assist with public outreach and media requests, and enhance the quality and consistency of NWS winter products and services as well. Version 2 of the National Snowfall Analysis (NSFAv2) addresses this need for a national, accurate, consistent, and seamless snowfall analysis to enable forecast verification. NSFAv2 will generate 24-hour estimates of snowfall on a CONUS grid at a resolution ranging between 2.5 and 5 km.  These estimates will be available for analysis periods ending at 00Z and 12Z each day. Snowfall analyses will be issued within one hour of the end of each analysis period, then will be regenerated and re-issued at least once per hour during 72 hours following the end of the analysis period. This schedule allows for early issuances of the analysis while also making use of valuable, late-arriving input data, particularly station observations and QPE data. The following categories of near-real-time input data are elements of the SNODAS operational data stream upon which the NSFAv2 is dependent: High Resolution Rapid Refresh quantitative precipitation forecasts (QPF), NCEP Stage IV quantitative precipitation estimates (QPE), downscaled and “corrected” Rapid Refresh (RAP) analysis temperatures, and historical precipitation and snowfall data from the Global Historical Climatology Network Daily (GHCND) dataset.  The NSFAv2 will generate a background, or “first-guess” snowfall grid for the analysis period based on bias-adjusted short-term NWP forecasts and climatological snow-liquid ratio (SLR) data; and will adjust this result by interpolating the differences between the background and station observations of snowfall.