Relationships between Gulf of California Moisture Surges and Precipitation in the Southwestern United States

Abstract

Relationships between Gulf of California moisture surges and precipitation in the southwestern United States are examined. Standard surface observations are used to identify gulf surge events at Yuma, Arizona, for a multiyear (July?August of 1977?2001) period, and Climate Prediction Center (CPC) precipitation analyses and NCEP?NCAR reanalysis data are used to relate the gulf surge events to the precipitation and atmospheric circulation patterns, respectively. Emphasis is placed on the relative differences in the precipitation and atmospheric circulation patterns for several categories of surge events, including those that are relatively strong (weak) and those that are accompanied by relatively wet (dry) conditions in Arizona and New Mexico after onset. It is shown that rapid surface dewpoint temperature increases are not necessarily a good indicator of increased rainfall in the region. The extent to which the precipitation and atmospheric circulation patterns are influenced by a phasing of tropical easterly and midlatitude westerly waves is also considered. Results indicate that a significant fraction of the events in all categories are related to the passage of westward-propagating tropical easterly waves across western Mexico. However, the occurrence of wet versus dry surges in the southwestern United States is not discriminated by the presence of tropical easterly waves, but rather by the relative location of the upper-level anticyclone in midlatitudes at the time of the gulf surge.