The more extreme nature of North American Monsoon precipitation in the Southwestern United States as revealed by a historical climatology of simulated severe weather events

Thang M. Luong, Christopher Castro, Hsin I. Chang, Timothy Lahmers, David K. Adams, Carlos A. Ochoa-Moya

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19 Scopus citations


Long-term changes in North American monsoon (NAM) precipitation intensity in the southwestern United States are evaluated through the use of convective-permitting model simulations of objectively identified severe weather events during "historical past" (1950-70) and "present day" (1991-2010) periods. Severe weather events are the days on which the highest atmospheric instability and moisture occur within a long-term regional climate simulation. Simulations of severe weather event days are performed with convective-permitting (2.5 km) grid spacing, and these simulations are compared with available observed precipitation data to evaluate the model performance and to verify any statistically significant model-simulated trends in precipitation. Statistical evaluation of precipitation extremes is performed using a peaks-over-threshold approach with a generalized Pareto distribution. A statistically significant long-term increase in atmospheric moisture and instability is associated with an increase in extreme monsoon precipitation in observations and simulations of severe weather events, corresponding to similar behavior in station-based precipitation observations in the Southwest. Precipitation is becoming more intense within the context of the diurnal cycle of convection. The largest modeled increases in extreme-event precipitation occur in central and southwestern Arizona, where mesoscale convective systems account for a majority of monsoon precipitation and where relatively large modeled increases in precipitable water occur. Therefore, it is concluded that a more favorable thermodynamic environment in the southwestern United States is facilitating stronger organized monsoon convection during at least the last 20 years.

Original languageEnglish (US)
Pages (from-to)2509-2529
Number of pages21
JournalJournal of Applied Meteorology and Climatology
Issue number9
Publication statusPublished - 2017



  • Atmosphere
  • Mesoscale models
  • North America
  • Precipitation
  • Regional effects

ASJC Scopus subject areas

  • Atmospheric Science

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