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An Examination of the Diurnal Cycle in the NCEP GFS (and Eta) Model Precipitation Forecasts (during NAME)

An Examination of the Diurnal Cycle in the NCEP GFS (and Eta) Model Precipitation Forecasts (during NAME). John Janowiak, Valery Dagostaro*, Vern Kousky, Bob Joyce Climate Prediction Center/NCEP/NWS, Camp Springs, MD Meteorological Development Laboratory/NWS, Silver Spring, MD.

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An Examination of the Diurnal Cycle in the NCEP GFS (and Eta) Model Precipitation Forecasts (during NAME)

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  1. An Examination of the Diurnal Cycle in the NCEP GFS (and Eta) Model Precipitation Forecasts (during NAME) John Janowiak, Valery Dagostaro*, Vern Kousky, Bob Joyce Climate Prediction Center/NCEP/NWS, Camp Springs, MD Meteorological Development Laboratory/NWS, Silver Spring, MD 30th Climate Diagnostics and Prediction Workshop, Penn State University, October 26, 2005

  2. MODEL FORECASTS Study Period: July 12 – August 15, 2004 (during NAME field campaign) Every 3 hours after 1st 12 hours from 00Z runs (12h, 15h, …, 36h) 1o 1o x lat/lon grid

  3. VALIDATION DATA • A new member of the “MORPH” family: “RMORPH” (Research-quality) • Land: CPC daily gauge analysis (Higgins & Shi) disaggregated by CMORPH • satellite estimates • Ocean: CMORPH only • Interpolated to match space-time resolution of model forecasts

  4. VALIDATION DATA • A new member of the “MORPH” family: “RMORPH” (Research-quality) • Land: CPC daily gauge analysis (Higgins & Shi) dissaggregated by CMORPH • satellite estimates • Ocean: CMORPH only • Interpolated to match space-time resolution of model forecasts

  5. RMORPH & Gauge Comparison

  6. Precipitation Difference from Validation Data mm/day mm/day

  7. Difference in Frequency (%) by Intensity Eta - RMORPH GFS - RMORPH Percentage Difference

  8. Distribution of Heavy Rainfall Events

  9. (Land only)

  10. Mean 3-hour Precipitation

  11. HARMONIC ANALYSIS Applied to period mean diurnal cycle

  12. HARMONIC ANALYSIS Applied to period mean diurnal cycle

  13. % of Daily Mean Precipitation @ 35oN

  14. Precipitation @ 35oN

  15. CONCLUSIONS • Peak daily rainfall 3-6 hrs too early in Eta (SE US) • and GFS (eastern U.S.) • Better phase agreement over NAME “Tier-1” • Models propagate rainfall well (central US -> east ) • Light rain rate OVERforecast in the models & • heavy events UNDERforecast

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