Heavy Rain in Garfield County, Colorado

Public reported flooding across State Highway 139 south of Douglas Pass due to several rounds of heavy rain training over the steep and saturated terrain. No reports of road closures or damages to the roadway.

The period between the 11th and 13th of September had a relatively unique meteorological setup for western Colorado and eastern Utah. A potent closed low was located over Southern California, and a ridge of high pressure was located to our southeast, directing a rich plume of monsoonal moisture northward through the Four Corners. Mixing ratios in this plume of moisture were more than high enough to not only help form strong to severe thunderstorms, but also to produce flash flooding and debris flows. Additionally, there was ample instability, with morning clearing helping 600-1000 J/kg of CAPE develop each afternoon. The region also fell under the right exit region of a potent upper level jet streak, which added additional lift and 40-50 kts of shear. Additionally, terrain effects added additional lift and shear. All together, this was a potent setup with the potential to produce severe thunderstorms. And indeed, the storms that developed produced not only large hail and strong, damaging winds, but also two tornadoes in Southeast Utah, and flash flooding across the area. Particularly, fresh burn scars, including the Lee and Elk RBX scars, saw substantial flash flooding and debris flows as storms trained over the area and produced very heavy rain. Finally, after 3 days of widespread severe weather, the cold front pushed through the region, and a cooler, drier, and above all, calmer airmass moved in, bringing an end to the event.