Summer Precipitation Regimes over North America and Prediction

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Summer Precipitation Regimes over North America
and Prediction

• Kingtse C. Mo Jae Schemm
• Climate Prediction Center
• NCEP/NWS

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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

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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)

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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.

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Northern Great plains
Southern Mexico
NW Mexico SW
Southern Plains
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Weak Tropical linkage ,Zonal pattern
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RPC 1 Southern Mexico
Both ENSO MJO can influence REOF 3
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Meridional mode
REOF 2
REOF 5
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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)
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OLRA
Submonthly mode
REOF 5
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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

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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

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Northern Plains GPLLJ
Northern Plains GPLLJ
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Southern Plains
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Beryle Paegle 2003
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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

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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

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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

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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

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1999July
2000Aug
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Seasonal Forecasts (July-September)

• GFS model 92 day forecasts
• 8- member ensemble ICs 6 h apart
• T62L28, T62L64 and T126L28
• Observed SSTs
• 1999 summer

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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

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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

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