The avalanche swept Patterson a total of 1,380 feet down the mountain, over "a couple of cliffs" and through areas with sparse trees, according to the report.
Patterson's family reported him missing Thursday night at about 7:30 p.m. According to the report, he checked in via phone before 1:30 p.m. but never contacted anyone again or returned home. Authorities spent the evening searching for him and spotted his body just before sunset.
The report describes the avalanche that killed Patterson as "small ... but a really bad ride."
Patterson a forecaster for the Utah Department of Transportation Snow and Avalanche Program was ascending a ridge on the east side of Kessler Peak on a track between two avalanche paths that are locally known as God's Lawnmower and Kessler Slabs. Patterson used climbing skins as he followed a "fairly standard up-track" used by both the public and UDOT forecasters.
But as Patterson neared the top of the northeast-facing ridge, his path led him onto a steep, east-facing slope. The snow in that area was wind-loaded, the report states, and as Patterson stepped out onto the slope he triggered the avalanche.
After falling, Patterson came to rest on the surface of the avalanche debris. He suffered trauma to his head and hip, the report states. Searchers discovered he had deployed an avalanche airbag, which is designed to keep a skier from being buried under the snow.
The report adds that two recent storms had dropped new snow onto a "pre-existing sun crust." Conditions were exacerbated by rapid warming Thursday. However, despite the danger, much of the snow had stabilized and "the distance of only a foot or two separated safe snow from dangerous snow," the report explains.
Investigators were unable to determine if Patterson had stepped out onto unstable slope by accident while making a switchback or if he planned to examine the snow there.
The report is accompanied by photos the Utah Avalanche Center members took while investigating the accident. The photos show Patterson's footprints up the mountain and the fracture lines from the slide.
The report echoes the comments of Patterson's boss, UDOT's highway avalanche safety program supervisor Liam Fitzgerald, who described Patterson as a skilled avalanche forecaster with an extensive background.
"After seeing the accident site and the avalanche conditions," the report states, "we all agreed that it was the kind of accident that could have happened to any of us."