Dangerous avalanche conditions exist. Approximately twenty inches of snow has fallen in the Southwest Trails area over the last two days. Strong winds have accompanied this snowfall, forming wind slabs in terrain above 7500 feet. In many areas, these slabs lie on smooth firm surfaces formed by very strong winds earlier in the week. These wind slabs could be easily human triggered, will increase in sensitivity today and could release naturally. Of equal or greater concern is the persistent slab problem in the area. Persistent weak snow layers are prevalent and have been strained by this new snow load. Avalanches involving them could initiate by the weight of a single person or as the result of triggering a smaller wind slab. If triggered these hard slab avalanches could be very large and unsurvivable. Cautious route finding and conservative decisions are a must today.
Weak faceted snow layers are preserved within the snowpack. Avalanches involving these layers could be human triggered today at all elevations and could have depths to five feet at the higher elevations.
Wind slabs could fail on Thursday's firm snow surfaces or on density breaks within the new snow with depths up to three feet in steep wind-loaded starting zones These slabs will increase in size and sensitivity as they are further loaded today.
( Discussion is generated from the previous day's afternoon forecast. )A winter storm warning remains in affect for the area through 11pm tomorrow. Although snowfall rates overnight are to be lighter, on Saturday moisture is to increase again with moderate to heavy snowfall expected through the day. Another 6 to 12 inches is possible by tomorrow night. Temperatures are to be similar to today’s with west to southwest winds having averages between ten and twenty mph. The general avalanche danger will be Considerable above 7500 feet and Moderate below that elevation. In all forecast areas at higher elevations, new, soft, wind slabs with depths to three feet could be triggered in steep leeward terrain. These slabs will become more sensitive as the day progresses. The other avalanche problem is a persistent slab problem. Although this problem also exists in all the forecast areas it varies greatly by area. In the Tetons, avalanches involving these old layers are becoming unlikely at higher elevations and remain more of a concern at lower elevations or in areas where the snowpack is shallow. At Togwotee Pass, the snowpack is much shallower, and weak layers are widespread and prominent. With enough new snow, human triggered avalanche activity involving these weaknesses will become likely. The Southwest Trails area is in between. In some areas, deep snow depths have made the triggering of very large avalanches less likely but in other areas, human triggered hard slab avalanches remain possible and careful snowpack assessment is both recommended and essential.
