A Synoptic and Mesoscale Investigation of the Extreme Precipitation Event over the Front Range of Colorado on 10-13 September 2013
A nearly stationary upper-level low across the western U.S. provided upper-level lift as well as mid-to-upper-level moisture from the Pacific while a stalled front over Northeastern Colorado provided surface convergence for mid-to-low-level moisture from the Gulf of Mexico. Persistent east-to-southeast winds over the Palmer Divide provided sufficient flow for the Denver Cyclone to set up. This contributed to the surface convergence found along the stationary front, as well as along the topographic gradient provided by the Front Range of the Rocky Mountains. The combination of the stationary front, Denver Cyclone and southwest winds aloft produced an environment with sufficient shear to maintain vortices normally associated with severe weather. These vortices allowed the strongest convective elements to tilt with height leading to efficient, long-lasting moderate rainfall which was the hallmark of this event.