Since the dry period ended on December 11th, over three feet of snow containing nearly three inches of moisture has fallen in the Southwest trails areas. Yesterday's storm started warm, ended cold and was accompanied by very strong winds that veered from the southwest to the northwest. Wind slabs could fail on density changes within the recent snow however the focus for safe backcountry travel needs to involve evaluation of the persistent slab problem which lies at the interface between the dry period and the recent snow. Skiers and riders have the potential to trigger slides involving these layers at all elevations but particularly above 7500 feet where they are larger and more likely.
Faceted snow and melt-freeze crusts formed during an extended dry period that ended on December 11th. Slabs above that layer could be triggered today. These slabs could be soft or hard with depths to three feet at the higher elevations and to eighteen inches at the low elevations. Be particularly wary of unsupported slopes and cliff areas.
( Discussion is generated from the previous day's afternoon forecast. )As the trough axis passes to the east, snow will taper off overnight first in the Tetons and then in the other forecast areas. A few more inches of snow could fall during this time. By morning, expect mostly clear skies and northwest winds to have decreased to averages of ten to fifteen miles per hour. The northwest flow is to keep temperatures on the cold side, with mountain highs near ten degrees and valleys reaching the low twenties. The general avalanche hazard will be remain elevated as the snowpack adjusts to its many recent changes. In the Tetons and Southwest Trails areas it will be Considerable above 7500 feet, while the lower elevations of those zones and the Togwotee Pass area is rated as Moderate. Skiers and riders will have the potential to trigger shallow wind slabs from todays storm however the primary consideration and focus needs to remain on the persistent slab problem. The need to focus on and evaluate the weak snow buried December 11 is because even though triggering these events on this layer may be less likely, the weakness exists in the same terrain as the wind slab problem, is harder to predict, and carries far more serious consequences.
