Event Title

Influence of Large-Scale Regime Transitions on Atmospheric River Events over Western North America

Presenter Information

W. Samuel Webber, M.S. Meteorology

Faculty Sponsor(s)

Jason Cordeira

Abstract

The Pacific-North American pattern (PNA) is a teleconnection pattern that characterizes mid-tropospheric flow configurations over North America that can have profound implications regional weather and climate response. Multiple studies have investigated how different phases of the PNA can influence atmospheric river (AR) events over western North America, however, the relationship between PNA regime transitions and AR events has not yet been explored. In this study, archived daily PNA values from the CPC are cross-referenced with NCEP sub-daily IVT along the western North American coast to construct time series analyses of PNA transitions and the resulting AR day likelihoods during the winter months. Analysis of the time-lagged transitions illustrate enhanced likelihoods of AR days along the Pacific Northwest (California and Oregon) coast during positive-to-negative (negative-to-positive) pre- and mid-transition phases as well as negative-to-positive (positive-to-negative) post-transition phases. Enhanced precipitation and streamflow response are confined to the northern U.S. West Coast for the majority of P2N transition duration while the effects are more pronounced and shifted southward for the majority of N2P transition duration. Future research efforts will investigate the forecast reliability of regime transitions and the conjunction of PNA transitions with other teleconnection pattern transitions, such as the Eastern Pacific Oscillation.

Location

Hartman Union Building Courtroom

Start Date

5-2-2019 2:00 PM

End Date

5-2-2019 3:00 PM

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May 2nd, 2:00 PM May 2nd, 3:00 PM

Influence of Large-Scale Regime Transitions on Atmospheric River Events over Western North America

Hartman Union Building Courtroom

The Pacific-North American pattern (PNA) is a teleconnection pattern that characterizes mid-tropospheric flow configurations over North America that can have profound implications regional weather and climate response. Multiple studies have investigated how different phases of the PNA can influence atmospheric river (AR) events over western North America, however, the relationship between PNA regime transitions and AR events has not yet been explored. In this study, archived daily PNA values from the CPC are cross-referenced with NCEP sub-daily IVT along the western North American coast to construct time series analyses of PNA transitions and the resulting AR day likelihoods during the winter months. Analysis of the time-lagged transitions illustrate enhanced likelihoods of AR days along the Pacific Northwest (California and Oregon) coast during positive-to-negative (negative-to-positive) pre- and mid-transition phases as well as negative-to-positive (positive-to-negative) post-transition phases. Enhanced precipitation and streamflow response are confined to the northern U.S. West Coast for the majority of P2N transition duration while the effects are more pronounced and shifted southward for the majority of N2P transition duration. Future research efforts will investigate the forecast reliability of regime transitions and the conjunction of PNA transitions with other teleconnection pattern transitions, such as the Eastern Pacific Oscillation.