Atmospheric Rivers and Their Role in Extreme Precipitation in the Midwest U.S.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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Two case studies are presented of atmospheric rivers ARs that produced heavy precipitation in the Midwest U.S. during March 2008 and October 2009. A third case study demonstrating an AR with normal precipitation in the Midwest also is included for comparison. The analyses used the Climate Forecast System Reanalysis CFSR data sets for identification of ARs and analysis. The study documents several key ingredients that contribute to differentiating between events of extreme precipitation and normal precipitation. The primary findings of this study are as follows 1 the induced flow due to the low-levelsurface temperature anomaly plays an important role in transporting moisture from the Caribbean northward to the Midwest 2 the induced wind field from a strong upper-level potential vorticity PV anomaly increases moisture flux from the Gulf and decreases static stability, which favors convective precipitation, and 3 heavy precipitation events are preceded approximately 9 hours by an increasing, positive moisture flux occurring across the northern Gulf Coast.
- Physical and Dynamic Oceanography