Dangerous avalanche conditions exist at the mid and high elevations. Skiers and riders have the potential to trigger surface slabs formed by recent snow and wind as well as deeper slabs involving persistent weak layers of snow and old crusts. As the next system arrives this afternoon the size and sensitivity of both of these hazards will increase. Yesterday several human triggered soft slab events were reported in the Tetons and a snowmobiler was partially buried after being caught and deploying his airbag in the Salt River range. Cautious routefinding and conservative decision-making is essential today.
Hard slab avalanches involving buried weak faceted snow laying over hard crusts formed in late November could be triggered with depths of two to four feet on a variety of aspects. Being caught in one of these dangerous slides could be fatal.
At the mid and upper elevations strong south to northwest winds have been and continue to form wind slabs on a variety of aspects. These slabs are forming on a variety of old snow surfaces including sun crusts and areas of recently formed surface hoar. These slabs could be human triggered on steep avalanche prone slopes with depths to 18 inches and have potential to step down to the deeper persistent weak layers.
The National Weather Service has issued a Winter Weather Advisory for the area through Friday at 5pm. By that time, an additional four to ten inches of snow is expected in the mountains, with two to six expected in the valleys. Southwest winds are to be very strong overnight with averages near forty miles per hour and gusts in the sixties. During the day, winds are to lessen to twenty to thirty mile per hour averages.The general avalanche hazard is expected to be Considerable above 7500 feet if moderate snowfall occurs but could increase to High if overnight and morning snowfall is at the upper end of or exceeds the predicted snowfall amounts. Below 7500 feet the hazard could rise to Moderate if significant snowfall occurs there where weak snow lies on north aspects between 7000 and 7500 feet. Regardless of the final ratings, avalanche conditions will be DANGEROUS at a minimum. Skiers and riders will have the potential to trigger both wind slabs that have been being formed since Tuesday as well as deeper slabs involving the persistent weaknesses that have posed a threat for weeks on all aspects.
