CW3E Event Summary: 16-19 May 2020

May 21, 2020

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A moderate and seasonally anomalous atmospheric river brought precipitation to a large portion of the Western US

  • Several coastal and inland locations across the Western US experienced AR 1 conditions on the Atmospheric River Scale
  • As much as 6 inches of precipitation fell over high elevation locations in the Sierra Nevada, Cascade, and Rocky Mountains
  • Coastal Sonoma County has only experienced IVT magnitudes greater than 650 kg m–1 s–1 during the later half of May twice since 2000
  • While this AR brought much needed precipitation to drought stricken Northern California, the Northern Sierra 8-Station index has only received 64% of its normal precipitation during water year 2020

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 15 May – 1800 UTC 20 May 2020

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of GFS Analysis

Valid 0000 UTC 15 May – 1200 UTC 20 May 2020








Summary provided by C. Hecht, B. Kawzenuk, C. Castellano, Z. Zhang, J. Kalansky, and F. M. Ralph; 2 PM PT 21 May 2020