Archived WESTERN WYOMING AVALANCHE ADVISORY Issued on Mon January 18, 2016 6:31 PM Note: This is archived for a fatality that occured on January 19. There are more specific area advisories but it is not clear, without local knowledge, which of their areas the incident was in. Therefore the general advisory issued the night before is archived here. SITUATION Western Wyoming was under overcast skies on Monday as a Pacific storm system brought light to moderate snowfall to the area. As this storm system moved through, flow aloft backed to the southwest. Mountain temperatures warmed into the low 20s as the valleys climbed into the low to mid 30s. Southwesterly to westerly ridgetop winds ranged from 15 to 30 miles per hour. Snowfall over the past several days became denser with each bout of moisture, and snow densities rose to around ten percent over the last 24 hours. This has created an upside-down snowpack. Snowfall totals since Wednesday night are close to five feet in the Tetons, which added over four inches of snow water equivalent to a snowpack with facets residing near its base. The Togwotee Pass snowpack, which is shallower and more faceted, received close to two feet of snow containing one and a half to two inches of water during this time period. Around two and a half feet of snow accumulated in the Greys River area, which added two inches of water weight. This snowfall increased settled snow depths in the Tetons to six to seven feet. The snowpack is between three and a half and four feet deep in the Togwotee pass area, and the Greys River forecast zone has five to five and a half feet of snow on the ground. Late this morning, an eight inch deep slide was triggered on an east-southeast facing aspect in the backcountry to south of the Jackson Hole Mountain Resort at an elevation of 8,500 feet. Two people were caught and carried, but not buried or injured. Several shallow natural events were also observed at the base of 25 Short in Grand Teton National Park. FORECAST FOR Tuesday, January 19, 2016 Snowfall will diminish by midnight, and a brief lull will ensue through most of Tuesday before the next storm system moves in late Tuesday afternoon. Periods of sunshine will be possible during the day. Overnight lows in the mountains will be in the low teens before rising into the low 20s in the afternoon. Westerly to northwesterly ridgetop winds will range from 10 to 20 miles per hour before backing to southwest with the approach of Tuesday night’s storm. The general avalanche hazard is expected to be Considerable on Tuesday and could increase on sunlit aspects as the day warms if any extended periods of sunshine occur. Wind slabs, with depths of one to three feet, could be triggered by backcountry travelers in steep, wind-loaded avalanche terrain. Deep persistent slab avalanches in the Tetons and Greys River area, and persistent slab avalanches in Togwotee Pass forecast zone, will remain possible. If triggered, these slabs will result in high consequences and could be up to six feet deep in the Tetons. In the Togwotee Pass and Greys River areas, slab depths could reach four and five feet, respectively. Large triggers, such as groups of people, may be needed to initiate one of these slides, particularly in the Tetons where the persistent weak layers are the deepest and most difficult to impact. The release of a surface slab could also step down to these basal facets. With the amount of loading that has occurred over the last week, a natural release of one of these deep hard slabs is not out of the realm of possibilities. A conservative approach to both terrain selection and decision making will be essential for safe travel on Tuesday. TREND FOR Wednesday, January 20, 2016 AND Thursday, January 21, 2016 Snowfall will continue Tuesday night and on Wednesday before ridging builds on Thursday. More snow will be possible into the weekend. Similar avalanche conditions will continue.