This week’s weather began with a fast moving cold front that passed over the region on Friday night. During the week conditions were very mild with overnight valley low temperatures on Monday and Tuesday nights in the 40’s. It ended with the passage of a weak cold front on Wednesday followed by mostly clear skies on Thursday. A backcountry skied died in an avalanche in Darby Canyon on the west side of the southern Teton Range on Saturday March 10th.

On Friday clouds increased ahead of an approaching cold front. This system brought several inches of snow and cooler temperatures. On Saturday skies cleared as the day progressed and the fast moving front moved east. Mountain temperatures fell into the teens Saturday night. Sunday was mostly cloudy with highs rising into the mid to low 30’s in the mountains. Temperatures on Sunday night dropped into the 20’s.

On Monday skies were partly cloudy with daytime highs rising into the 40’s in the mountains and into the 50’s in the valleys. On Monday and Tuesday nights overnight lows fell only into the low 30’s or upper 20’s at 10,500 feet and stayed in the mid 40’s in the valleys. This period of above freezing temperatures melted much of the existing shallow snowpack on the valley floors.

Figure 19.1 Graph of air temperatures at the base study plot at the Jackson Hole Mountain resort for the period of March 9th through March 16th

The passage of a weak cold front brought slightly cooler temperatures and clouds to the region on Wednesday. Skies cleared on Wednesday night and temperatures fell into the teens in the mountains. On Thursday temperatures rose into the upper 20’s to low 30’s in the mountains and into the 40’s in the valleys.

At the end of the week steep south facing slopes below 7,000 feet were mostly bare of snow as were some level open areas below 6,500. North facing and shaded aspects at these elevations still retained up to three feet of snow. Total snow depths at elevations of 9,000 to 9,500 feet were 70 inches at the Jackson Hole Mountain Resort, 95 inches at Grand Targhee Resort, 71 inches at the Blind Bull Summit in the Wyoming Range and 56 inches near the top of Togwotee Pass. As of March 16th the mid mountain study plot at the Jackson Hole Mountain resort had only received 9 inches of new snow since March 1st.

On Saturday two backcountry travelers in Darby Canyon on the west side of the Teton Range triggered a hard slab avalanche in the starting zone of a well defined avalanche path (Figure 19.2).

Figure 19.2 Photograph of the slide path in Darby Canyon where a backcountry skier died in an avalanche on March 10th

Two brothers were ascending when the slab they were upon failed and caught them both. One was on a splitboard and above the other. He was carried approximately 200 vertical feet and was not injured. The other brother, who was on telemark skis and below his sibling on the same slope, was carried a long distance and buried under several feet of avalanche debris near the toe of the slide.

The area of the avalanche starting zone where failure of this slab occurred was reported by Don Sharaf, who investigated this incident, to face northwest and have a steepness of 36 to 39 degrees. The slab was hard and underlain by faceted snow. In the area where the avalanche was triggered this slab was shallow (8 to 12 inches deep). The thickest section of the crown of this slab was just over three feet deep. Rock bands and boulders extrude from the shallow snowpack in this area of the starting zone (Figure 19.3).

Figure 19.3 Starting zone of the avalanche that killed a backcountry skier on March 10th

The victim was carried approximately 1700 vertical feet. He had an avalanche beacon and was located and uncovered by his brother who then performed CPR until rescuers arrived. The cause of death was reported to have been trauma and suffocation.

There were several inches on new snow on the morning of the 10th. On Saturday morning skies were cloudy with light snow. The skies cleared as the day progressed. At the Raymer Plot at the Jackson Hole Mountain Resort the air temperature reached 29 degrees at 2 PM. This avalanche is believed to have occurred at about 5 PM.