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Summer Precipitation Regimes over North America and Prediction

Summer Precipitation Regimes over North America and Prediction. Kingtse C. Mo & Jae Schemm Climate Prediction Center NCEP/NWS. Purposes. 1. Identify Summer Precipitation Regimes over Mexico and the United States 2 Determine P regimes are related to Tropical convection

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Summer Precipitation Regimes over North America and Prediction

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  1. Summer Precipitation Regimes over North America and Prediction Kingtse C. Mo & Jae Schemm Climate Prediction Center NCEP/NWS

  2. Purposes • 1. Identify Summer Precipitation Regimes over Mexico and the United States • 2 Determine P regimes are related to Tropical convection • 3. Influence of soil moisture on P regimes • 4 Week2 to Seasonal Forecasts

  3. Data sets *Precipitation over Mexico and the United States (1968-2002) * Circulation anomalies: CDAS/reanalysis R1 1968-2002 * OLRA : 1979-2002 ( Total & IS 10-90 day filtered) * Qfluxes (vertically integrated moisture flux) from CDAS 1968-1996, RSM 1991-2000 * Soil moisture and E from an off line NAOH model 1968-1998 (Huug van Den Dool et al. 2003)

  4. Methods Pentad precipitation data from June-September 1979-2002 Square root transformation to make rainfall close to a normal distribution Perform EOF analysis Rotated EOF 5 day running mean of P and take square root take out the mean and project onto REOF to get RPCs.

  5. Northern Great plains Southern Mexico NW Mexico & SW Southern Plains

  6. Weak Tropical linkage ,Zonal pattern

  7. RPC 1 Southern Mexico Both ENSO & MJO can influence REOF 3

  8. REOF 2 Meridional mode REOF 5

  9. MJO When suppressed convection shifts to the central Pacific, Central America is likely to be wet (REPF 3), more rainfall over northwestern Mexico & less rainfall over southern Great Plains (REOF 2)

  10. OLRA Submonthly mode REOF 5

  11. Four REOF patterns related to the NAMs REOF 1- Continental Zonal pattern, weak tropical influence REOF 3- Southern Mexico Both ENSO and MJO influence REOF 2 & REOF 5- Phase reserval Northwestern Mexico & southern Plains – Intraseasonal oscillations influence

  12. Northern & Southern Great Plains • They belong to two REOFs (REOF 1 & 5) • They both are controlled by the Great Plains LLJ • REOF 1 rainfall is influenced by soil moisture at the entrance region of the GPLLJ,but not REOF 5

  13. Northern Plains GPLLJ Northern Plains GPLLJ

  14. Southern Plains

  15. Beryle &Paegle 2003

  16. RPC 1 Continental P pattern • Zonal pattern (Cavazos et al2002) • Strong GPLLJ & weak GCLLJ • Associated with strong upper level wind over the west region. (Beryle & Paegle2003) • Weak tropical convection • Wet soil moisture anomalies near the entrance of the GPLLJ 10 days before positive events

  17. REOF 3 – Southern Mexico • Strong influence from tropical convection in the tropical Pacific. Both the MJO and ENSO can influence rainfall over Central America and REOF 3

  18. REOF 2 & REOF 5 Northwestern Mexico, the Southwest & southern Plains • Phase reversal between the GPLLJ and the GCLLJ • Meridional pattern • No precursor of soil moisture influence • Influenced by tropical intraseasonal oscillations

  19. Monthly ForecastsCase studies • July 1999 – A very wet Southwest • August 2000- A dry Southwest • Four members in the ensemble • T62L28 forecasts– 50 km RSM downscaling

  20. 1999July 2000Aug

  21. Seasonal Forecasts (July-September) • GFS model 92 day forecasts • 8- member ensemble ICs 6 h apart • T62L28, T62L64 and T126L28 • Observed SSTs • 1999 summer

  22. Seasonal Forecasts • High resolution model is needed to capture rainfall over the Southwest • Future Plans a) Systematically test the impact of model resolution (T126L64, T170L28) b) Radiation & diurnal cycle c) Test of convection d) T62L28 downscaling with RSM & T170L28

  23. 30 day forecasts (calibration run)Jae Schemm • JJAS from 1998-2002 • T126L28 for 7 days  T62L28 to 30 days • Errors for T126L28 and T62L28 are very different

  24. REOF 1 black REOF 2 Green REOF 3 Red REOF 5 blue

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