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WRF Verification:

WRF Verification:. Chris Davis NCAR (MMM/RAP). New Methods of Evaluating Rainfall Prediction. Collaborators: Dave Ahijevych, Mike Baldwin, Barb Brown, Randy Bullock, Jennifer Mahoney, Kevin Manning, Rebecca Morss, Stan Trier, John Tuttle and Wei Wang. WRF Verification Effort. Case studies

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WRF Verification:

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  1. WRF Verification: Chris Davis NCAR (MMM/RAP) New Methods of Evaluating Rainfall Prediction Collaborators: Dave Ahijevych, Mike Baldwin, Barb Brown, Randy Bullock, Jennifer Mahoney, Kevin Manning, Rebecca Morss, Stan Trier, John Tuttle and Wei Wang

  2. WRF Verification Effort • Case studies • Real-time forecasts • Extended-period case studies • Idealized tests of physical parameterizations • Application of new verification methods

  3. Objectives of New Verification Methods • Reduce dimension of verification problem • Make statistics sensitive to error magnitude • Address and target fundamental processes in models • Provide useful feedback to developers and users • Make automated, yet insightful

  4. Daily Cycle of Rainfall (Echo Frequency) 00 Z “Standard”: 102-110 W “Out of phase”:96-102 W Semidiurnal: 92-96 W Mainly Diurnal: 78-92 W 12 Z 00 Z 110 W 102 W 94 W 86 W 78 W

  5. Diurnal Rainfall Signatures in NWP models Models: • NCEP Eta: hydrostatic, 22-km, 50 levels, eta (step-mountain) coordinate, two-phase ice, Betts-Miller-Janjic cumulus scheme, MYJ boundary layer, OSU land surface model. Two 48-h forecasts per day. • Weather Research and Forecast Model (WRF): nonhydrostatic, 22-km, 28 levels, height-coordinate, two-phase ice, Betts-Miller-Janjic cumulus scheme, MRF boundary layer, slab surface model. Two 48-h forecasts per day. Method: • Compile 3-hourly precipitation forecasts and analyses for July and August 2001. • Analyze all data to common 10-km grid. • Average precipitation from 30 N – 45 N. • Assume “echo” is averaged 3-h rainfall > 0.1 mm.

  6. Stage IV GMT Diurnal Hovmoller Diagrams: 22-km Eta and WRF 00Z Eta 12-36 h 00Z WRF 12-36 h GMT 12Z Eta 12-36 h 12Z WRF 12-36 h GMT ? Longitude Longitude

  7. Diurnal Hovmoller Diagrams: 10-km WRF

  8. An Example of Rainfall Prediction Errors Left: 24-42 h forecasts from WRF model Right: Observations from NCEP analysis Gray: 40% echo freq. from 4-year climatology 110 W 78 W

  9. Time-Latitude Diagrams Stage IV WRF August, 2001 Latitude Latitude 30 N 45 N 30 N 45 N

  10. O F O F F O O F What does CSI=0 (or ETS=0) mean to you? In all cases: POD=0, FAR=1, CSI=0

  11. A Proposed Approach(based somewhat on Ebert and McBride) • Define precipitation/convective objects and shapes • Diagnose errors in location, shape, orientation, size, timing, etc. • Characterize basic attributes of precipitation/convection within objects: intensity, density, etc. • In parallel: Investigate user issues

  12. Defining objects Original WRF forecasts from 10-km grid Convolved Thresholded

  13. Fitting shapes:Reduce objects to small number of parameters

  14. Summary and Issues Rainfall Statistics • Large NWP-model errors (WRF, Eta) in the diurnal and propagating aspects of warm-season rainfall • Better representation of latitude of rainfall than longitude • Do we need cloud-resolving grids to capture properly?

  15. Summary and Issues (continued) Rain-area Verification • Method yields errors on location (x,y,t), size and orientation of rain areas and allows partitioning of areas with similar attributes • PDFs of rainfall intensity are evaluated: appropriate for application to inherently stochastic processes • How will this improve models more readily than “traditional” methods (ETS, bias)? • Intensity PDF contains more information than bias: strongly tied to cumulus and/or cloud physics schemes • Systematic shape errors could indicate problems in identifying modes of organized convection • Systematic timing/location errors could point to errors in treating diurnal and orographic effects

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