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J. Paul Dallavalle and Valery J. Dagostaro Meteorological Development Laboratory

Objective Interpretation of Numerical Weather Prediction Model Output – A Perspective Based on Verification of Temperature and Precipitation Guidance. J. Paul Dallavalle and Valery J. Dagostaro Meteorological Development Laboratory National Weather Service/NOAA

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J. Paul Dallavalle and Valery J. Dagostaro Meteorological Development Laboratory

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  1. Objective Interpretation of Numerical Weather Prediction Model Output – A Perspective Based on Verification of Temperature and Precipitation Guidance J. Paul Dallavalle and Valery J. Dagostaro Meteorological Development Laboratory National Weather Service/NOAA Symposium on the 50th Anniversary of Operational Numerical Weather Prediction June 14-17, 2004 University of Maryland College Park, MD

  2. Outline • History of NWS verification program • Methodology • Results • Conclusions

  3. History of NWS Verification Program • April 1966 – begins • Initially compared NMC subjective guidance and NWS local forecasts for max/min temperature and PoP • April 1970 –perfect prog max/min guidance replaces NMC guidance • January 1972 – MOS PoP guidance replaces NMC guidance • August 1973 – MOS max/min guidance replaces perfect prog guidance

  4. Max/Min Temperature Probability of Precipitation Local forecast is for daytime max/nighttime min Local forecast is for 1200-0000 UTC (day) and 0000-1200 UTC (night) Forecast Elements

  5. 0000 UTC cycle (* Added in October 1975 for temperature; in Summer 2002 for PoP) 1200 UTC cycle Today Tonight Tomorrow Tomorrow Night * Tonight Tomorrow Tomorrow Night Day after Tomorrow * Forecast Projections

  6. Methodology • 80 CONUS sites • Verification statistics for warm (Apr. - Sept.) and cool (Oct. – Mar.) seasons • “Official” verification observation • “Official” guidance • Fixed climate standard (1961- 90 normals for max/min; 1972- 85 relative frequencies for PoP)

  7. Verification Sites

  8. Verification Measures • Max/Min Temperature • Mean Absolute Error • PoP • Improvement in Brier Score relative to climate

  9. Significant Changes to “Official” Guidance • January 1972 -- PE-based MOS PoP • August 1973 -- PE-based MOS max/min • April 1980 -- LFM-based MOS • November 1985 -- daytime max/nighttime min • June 1993 -- NGM-based MOS • Summer 2002 -- GFS-based MOS

  10. Max Temperature – Cool Season (0000 UTC Cycle)

  11. Max Temperature – Warm Season (0000 UTC Cycle)

  12. Min Temperature – Cool Season (1200 UTC Cycle)

  13. Min Temperature – Warm Season (1200 UTC Cycle)

  14. PoP – Cool Season(0000/1200 UTC Cycles Combined)

  15. PoP – Warm Season(0000/1200 UTC Cycles Combined)

  16. Conclusions • Public weather forecasts and guidance have improved during the period • Quality of day 2 local forecasts now is equal to that of the day 1 forecasts ~ 20 years ago • Quality of day 2 guidance now is equal to that of the day 1 guidance ~ 10 years ago • Skill of PoPs is higher in cool season; errors in max/min are greater in cool season, but so is rate of improvement • High correlation between quality of guidance and local forecasts

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