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

Between North America’s Sierra Madre and Rocky Mountains exists a little-recognized terrain “gap.” This study defines the gap, introduces the term “Chiricahua Gap,” and documents the role of easterly transport of water vapor through the gap in modulating summer monsoon precipitation in southeastern Arizona. The gap 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 along a 3000-km length of the Continental Divide from 16°-45°N, and represents 80% of the total cross sectional area below 2.5 km MSL open to horizontal water vapor transport. This study uses reanalyses and unique upper-air observations in a case study and a climatology over two summers to show that 77% (94%) of the top-quartile (decile) monsoon precipitation days in southeast Arizona during 2009-2010 occurred in conditions with easterly water vapor transport through the Chiricahua Gap.