A journal article entitled The Landfall and Inland Penetration of a Flood-Producing Atmospheric River in Arizona. Part 1: Observed Synoptic-Scale, Orographic, and Hydrometeorological Characteristics, by P. J. Neiman, et al., was published in the April 2013 issue of the Journal of Hydrometeorology.
Atmospheric rivers (ARs) represent a dominant mechanism for generating intense wintertime precipitation along the west coast of midlatitude continents, including the U.S. West Coast. While studies over the past 10 years have explored the impact of ARs in, and west of, California's Sierra Nevada and the Pacific Northwest's Cascade Mountains, their influence on the weather across the intermountain west remains an open question.
This study uses atmospheric data in the form of satellite imagery, wind and GPS measurements, and operational hydrometeorological observing networks to explore the causes and inland impacts of a landfalling, flood-producing AR across Arizona in late January 2010. Several types of analyses identify processes that led to widespread rain and snowfall across the state. The analyses show that a strong AR formed in the lower midlatitudes over the northeastern Pacific Ocean due to internal storm dynamics and evaporation from the warm sea surface, but the AR was not influenced by tropical moisture to the south. Observations in the AR document strong air motion rising over the mountains, which led to extreme rain and snowfall. The diagram at right shows that the AR was almost perpendicular to the Mogollon Rim, a steep slope crossing much of central Arizona, and it was positioned between the high mountain ranges of northern Mexico. High melting levels during the heaviest rainfall contributed to region-wide flooding, while the high-altitude snowpack increased substantially. The characteristics of the AR that impacted Arizona in late January 2010, and the resulting heavy precipitation, are comparable to those of landfalling ARs and their impacts along the west coasts of midlatitude continents.
Contact: Paul Neiman
Neiman, P. J., F. M. Ralph, B. J. Moore, M. Hughes, K. M. Mahoney, J. M. Cordeira, and M. D. Dettinger, 2013: The Landfall and Inland Penetration of a Flood-Producing Atmospheric River in Arizona. Part I: Observed Synoptic-Scale, Orographic, and Hydrometeorological Characteristics. J. Hydrometeor., 14, 460–484, doi:10.1175/JHM-D-12-0101.1.