1. Surface Transportation Weather Research Center University of North Dakota Pavement Precipitation Accumulation Improved Winter Precipitation Algorithm Presenter: Mark Askelson University of North Dakota Department of Atmospheric Sciences/RWIC/STWRC

2. Surface Transportation Weather Research Center University of North Dakota STWRC-Improved Winter Precipitation Algorithm 2 Improved Winter Precipitation Algorithm Algorithm Design Radar Data Decoder Clutter and AP Filter Snow Accum. Algorithm Radar Alg. Output Surface Obs. Decoder Blend Surface and Radar Radar + Surface Output Satellite Data Decoder Train Satellite from Radar + Surface Fill Holes Radar + Surface + Satellite Output Analyse s/Model Blending Algorithm Final Output

3. Surface Transportation Weather Research Center University of North Dakota STWRC-Improved Winter Precipitation Algorithm 3 Improved Winter Precipitation Algorithm Radar Data Bureau of Reclamation snowfall accumulation algorithm Developed in late 1990’s State-of-the-art radar algorithm Surface Data Adjust radar-based values—bias correction Yes/no flags to refine snowfall area

4. Surface Transportation Weather Research Center University of North Dakota STWRC-Improved Winter Precipitation Algorithm 4 Improved Winter Precipitation Algorithm Satellite data Geostationary Orbiting Environmental Satellites (GOES) Cloud Top Pressure Data Estimates of atmospheric pressure at top of clouds Available every hour Idea: cloud top pressure is related to snowfall rate. Deeper systems more likely to produce heavier snowfalls. Main function: fill holes

5. Surface Transportation Weather Research Center University of North Dakota STWRC-Improved Winter Precipitation Algorithm 5 Improved Winter Precipitation Algorithm Concerns Create snowfall where it is not present. → Must evaluate. → Use surface data to prevent? Accuracy → Same cloud tops will likely produce different snowfall rates in different systems. → Will train using combined radar and surface observation data.

6. Surface Transportation Weather Research Center University of North Dakota STWRC-Improved Winter Precipitation Algorithm 6 Improved Winter Precipitation Algorithm First Generation (Complete) Based on level III radar data Second Generation Based on level II radar data Progress Many base level radar routines completed Level II data decoder Components of satellite processing software Radar-based liquid water equivalent snowfall rate (mm hr -1 ) at 6.a.m. on 25 January 2004. From early version of PPAES.