July 2016 SW Climate Outlook - Monsoon Tracker

The southwestern monsoon officially starts June 15 and ends September 30 – the dates the National Weather Service began using in 2008 to identify the window of typical activity for the region. The historical start date of monsoon activity (increased dew point, onset of precipitation events) varies across the region and is reflected in a generally westward migration over the season (Fig. 1). The monsoon ridge also shifts throughout the season, and the location of this ridge helps determine where storms and precipitation events will occur.

The Southwest saw a strong start to the monsoon in the second half of June, with a number of heavy rainfall events, particularly across southern Arizona. Most of July has been characterized by a monsoon “break” for the Southwest, with very few precipitation events other than in the southeastern corner of Arizona. Since the start of the monsoon, most of Arizona and New Mexico have recorded below-average precipitation (Figs. 2a-b), but this is early in the season and a wide range of precipitation totals and considerable spatial variability is to be expected at this point (Figs. 3a-b). The percent of days with rain highlights the irregular coverage of monsoon precipitation thus far, with much of the heavy precipitation activity clustered in southeastern Arizona and across much of New Mexico (Figs. 4a-b).