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Disentangling the roles of internal atmospheric variability and ENSO on California precipitation to explain recent seasonal forecast errors
  • +9
  • Kristen Guirguis,
  • Benjamin J Hatchett,
  • Michael J DeFlorio,
  • Alexander Gershunov,
  • Rachel E. S. Clemesha,
  • W. Tyler Brandt,
  • Kayden Haleakala,
  • Christopher M Castellano,
  • Rosa Luna Nino,
  • Alexander Tardy,
  • Michael Anderson,
  • F. Martin Ralph
Kristen Guirguis
Scripps Institution of Oceanography, Univ. California, San Diego

Corresponding Author:[email protected]

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Benjamin J Hatchett
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Michael J DeFlorio
Scripps Institution of Oceanography
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Alexander Gershunov
Scripps Institution of Oceanography, Univ. California, San Diego
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Rachel E. S. Clemesha
Scripps Institution of Oceanography, University of California, San Diego
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W. Tyler Brandt
Scripps Institution of Oceanography
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Kayden Haleakala
University of California Los Angeles
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Christopher M Castellano
Scripps Institution of Oceanography
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Rosa Luna Nino
Scripps Institution of Oceanography
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Alexander Tardy
NOAA/National Weather Service, San Diego, CA
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Michael Anderson
California Department of Water Resources
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F. Martin Ralph
SIO
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Abstract

Water years (WY) 2017 and 2023 were anomalously wet for California, each helping to terminate multiyear droughts. In both cases, this was unexpected given La Niña conditions, with most seasonal forecasts favoring drier-than-normal winters. We analyze over seven decades of precipitation and snow records along with mid-tropospheric circulation to identify recurring weather patterns driving California precipitation and Sierra Nevada snowpack. Tropical forcing by ENSO causes subtle but important differences in these wet weather patterns, which largely drives the canonical ENSO-precipitation relationship. However, the seasonal frequency of these weather patterns is not strongly modulated by ENSO and remains a primary source of uncertainty for seasonal forecasting. Seasonal frequency of ENSO-independent weather patterns was a major cause of anomalous precipitation in WY2017, record-setting snow in WY2023, and differences in precipitation outcome during recent El Niño winters 1983,1998 and 2016. Improved understanding of recurrent atmospheric weather patterns could help to improve seasonal forecasts.
21 May 2024Submitted to ESS Open Archive
21 May 2024Published in ESS Open Archive