WRF Modeling of the 2014 Record Rainfall and Monsoon Flooding in Arizona

The Phoenix flash flood of September 7-8^th, 2014 is investigated in this Weather Research and Forecasting (WRF) modeling study. Our goal is to simulate the general features of the boundary layer in Arizona prior to and during the flash flood events and to study the related hazardous weather patterns. This study explores the impact of GC SSTs on factors affecting deep convective precipitation: the regional atmospheric circulation, water vapor mixing ratio, convective available potential energy (CAPE) and convective inhibition (CIN). The impact of Hurricane Norbert is also addressed.

Our WRF modeling study supports the hypothesis that Sea Surface Temperatures (SSTs) higher than usual for early September significantly enhanced the intensity of Norbert and influenced the rainfall rates and the intensity of the flash flood. In particular, the onset of the heavy rainfall occurs after the SSTs exceeded 29^oC. Here we explore this idea in a modeling context using the WRF to simulate the 2014 Arizona flood. To test this hypothesis, we investigate boundary layer and the atmospheric circulation in Arizona before and during the heavy rain events. Both the boundary layer water content and CAPE over Maricopa County, and the atmospheric circulation over Arizona changed dramatically over the course of the numerical simulations. WRF ARW (Advanced Research WRF model) successfully simulated the boundary layer properties and CAPE during the flood. Model validations with satellite and radar products demonstrate the skill of the WRF model in predicting CAPE, CIN, precipitable water, wind and total precipitation field conditions during September 2014 flash flood significant events. The WRF model did a good job at reflecting the actual events that occurred on September 8th, 2014. As model resolution is refined, the model remains stable, and most variables are in agreement with observations. The simulated Norbert moisture movement agrees with the onset of the heavy rainfall, triggers strong winds, damaging rain, and thunderstorms for several days across Arizona. These are serious life and aviation hazards.