A midlevel Pacific low pressure system undercut the area of high pressure over the Great Basin as it dropped into the Northern Rockies. Monsoon moisture increased across the region with precipitable water values ranging from 125 to 175% of normal across the Four Corners. Clearing conditions the morning of the 20th led to increased instability over southeast Utah which led to some stronger thunderstorms during the late evening hours. The anomalously high moisture values across the area resulted in heavy rain with thunderstorms. Additionally, winds aloft supported the training of thunderstorms. This heavy rainfall led to widespread flash flooding and debris flows across portions of Grand and San Juan counties.

Flash Flood in GRAND, UTAH
From 20-AUG-22 20:00:00 to 20-AUG-22 20:00:00 (MST-7)
Location: MOAB
Flood cause: Heavy Rain
Property damage: 9.50M
Crop damage: 0.00K
Reported by: NWS Storm Survey

Training thunderstorms produced upwards of 1 to 2 inches of rain within one to two hours in an around Moab. The Mill Creek Parkway - a recreational path that runs through the center of Moab, was reported to be ���completely decimated��� as a result of the flooding. Several areas had their water turned off after flood waters led to a broken water main.  Numerous homes and businesses had upwards of 12 inches of water and debris inside resulting in significant property damage.

Flash Flood in SAN JUAN, UTAH
From 20-AUG-22 19:00:00 to 20-AUG-22 19:00:00 (MST-7)
Location: GRAND CO ARPT
Flood cause: Heavy Rain
Property damage: 0.25K
Crop damage: 0.00K
Reported by: Park/Forest Service

White Rim Road in Canyonlands National Park was washed out at Upheaval Wash as a result of heavy rain from thunderstorms. A vehicle was hanging over the edge of the washed out road.

Flash Flood in GRAND, UTAH
From 20-AUG-22 21:00:00 to 20-AUG-22 21:00:00 (MST-7)
Location: MOAB
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Debris from Mill Creek flowed into the Colorado River as a result of heavy rain from thunderstorms.

Debris Flow in SAN JUAN, UTAH
From 20-AUG-22 19:00:00 to 20-AUG-22 19:00:00 (MST-7)
Location: GRAND CO ARPT
Flood cause: Heavy Rain
Property damage: 0.25K
Crop damage: 0.00K
Reported by: Park/Forest Service

A debris flow occurred as a result of heavy rain from thunderstorms on Shafer Basin Road in Canyonlands National Park.

Flash Flood in GRAND, UTAH
From 20-AUG-22 19:30:00 to 20-AUG-22 19:30:00 (MST-7)
Location: MOAB
Flood cause: Heavy Rain
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Broadcast Media

Several feet of water flowed through a neighborhood in Spanish Valley as a result of heavy rain from thunderstorms.

Flash Flood in GRAND, UTAH
From 20-AUG-22 19:30:00 to 20-AUG-22 19:30:00 (MST-7)
Location: MOAB
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Areas along Mill Creek experienced flash flooding as the creek overflowed due to heavy rain from thunderstorms. Water flowed over a park bridge, a dam had damage as an 18 inch diversion pipe cracked and filled with sand, and debris backed up on culverts which resulted in significant overland flooding.