The Chiricahua Gap and the Role of Easterly Moisture Transport in Southeastern Arizona Monsoon Precipitation

Between the Sierra Madre and Rocky Mountains exists a terrain “gap” that is potentially important to southwestern U.S. weather and climate.  The “Chiricahua Gap”, named after the Chiricahua Mountains located in southeast Arizona just west of the gap, is defined here.  It is near the Arizona/New Mexico border north of Mexico, and is approximately 250 km wide by 1 km deep.  It is the lowest section of the Continental Divide from 16–45N, and represents 80% of the total cross sectional area below 2.5 km MSL open to horizontal atmospheric water vapor transport across roughly 3000 km of the Continental Divide.  The aim of this presentation is to introduce the Chiricahua Gap, and discuss its potential influence on monsoon precipitation over southeast Arizona through climatology, composite, and case study analyses. We will utilize unique upper-air observations and the Climate Forecast System Reanalysis.

Results show that a monsoon burst, defined here as the upper-quartile of area-averaged daily rainfall over southeast Arizona, on 13–14 August 2009 occurred as easterly winds transported water vapor westward through the gap into southeastern Arizona contributing to 39% of that month’s precipitation in the area.  From a seasonal perspective, 75% of the monsoon bursts in southeast Arizona in 2009 and 2010 occurred in conditions with westward water vapor transport through the Chiricahua Gap. The synoptic-scale flow patterns that drive water vapor transport through the gap will be discussed.