The North American Monsoon System: Recent Evolution and Current Status

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The North American Monsoon System Recent
Evolution and Current Status
Update prepared by Climate Prediction Center /
NCEP 31 August 2009
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Outline

• Recent Evolution and Current Conditions
• Summary
• Climatology

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Rainfall Patterns Last 7 Days
During the past 7 days, near-average rainfall was
observed over Southwest U.S. and northwest Mexico.
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Rainfall Patterns Last 30 Days
During the past 30 days, belowaverage
precipitation was observed over most of the NAM
domain.
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Recent Evolution Rainfall
Top over Arizona, US, rainfall was slightly
below normal during the past week. Bottom
Below-normal precipitation over central and
southern Mexico during the past week.
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Atmospheric Circulation OLR Last 7 days

• During the past five days, OLR anomalies were
  positive over most of the NAM domain, consistent
  with the drier-than-average condition in the
  region.

Upper-level anticyclone was not evident over the
NAM domain during the last 7 days, consistent
with below-average precipitation in the NAM
domain during the period.
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NCEP/GFS Model Forecasts Bias-Corrected Precip.
Anom. for Weak 1 Week 2
Week-1
Week-2
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Summary

• Near-average rainfall was observed over Southwest
  U.S. and Northwest Mexico during the past 7 days.
• Although the NCEP Global Forecast System predicts
  near-average precipitation over the southwestern
  U.S in the next two weeks, Hurricane Jimena is
  expected to bring substantial rainfalls to the
  region in the next few days.

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ClimatologyMONSOON ONSET


July 9
July 13
July 14
July 7
July 8
July 13
July 3
July 6
July 11
June 27
June 25
June 29
June 23
June 22
June 21
June 17
June 16
June 14
June 14
June 10
June 11

June 8
June 7
Higgins, R. W., Y. Chen and A. V. Douglas, 1999
Interannual Variability of the North American
Warm Season Precipitation Regime. J. Climate,
17, 653-680
June 6
June 6
June 5
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Precipitation Climatology