Continued snowfall and very strong winds will quickly form new surface slabs as well as rapidly add load to persistent weak layers that are buried within the snowpack. The chance to trigger either of these avalanche problems will increase throughout the day as dense snow accumulates and winds veer from the southwest to the northwest. Dangerous avalanche conditions exist and natural avalanche activity will be possible at the higher elevations by the end of the day. Cautious route finding and conservative decision making is the best way to avoid involvement in hard to predict persistent slab avalanches.
New snow is forming wind slabs over faceted snow, surface hoar and crusts above 8000 feet. These slabs will increase in size and sensitivity as the day progresses and could have depths to a foot by later this afternoon.
The relatively wet and heavy snow that is falling will quickly add stresses to buried weaknesses in the snowpack. Although the level of weakness varies by location, these layers can generally be found at all elevations and most aspects. Release of these slabs is hard to predict and failure could occur after a slope is tracked when a weak or thin spot on a slope is impacted. By the end of the day, potential slab depths could reach five feet at the higher elevations and two feet at low elevations where the snowpack structure is poor.
( Discussion is generated from the previous day's afternoon forecast. )A Winter Weather Advisory is in effect through 11pm Wednesday evening. As moisture increases with the incoming system, snowfall will develop overnight. A few inches of snow is expected by sunrise with storm totals by late Wednesday of five to ten inches in the Teton and Southwest areas, and four to six inches in the Togwotee Pass area. Warmer air is associated with this system and some of the precipitation may fall as a mix of rain and snow in the valleys. Upper elevations are to have highs in the mid-twenties. Strong west to southwest winds are to accompany the event with averages of 25-40 mph. The general avalanche danger is likely to be Considerable in the Teton and Southwest Trails areas above 7500 and Moderate below that elevation. In the Togwotee Pass area, it will likely be Moderate at all elevations. If snowfall and/or winds are higher than forecast the danger rating may increase. Regardless of the rating, there will be increasing danger throughout the day tomorrow as new snow and wind form sensitive surface slabs on the existing snow surfaces. The likelihood of triggering deeper instabilities will also increase during the day as potentially an inch of moisture is quickly added to a snowpack with widespread weaknesses. Slab depths involving these old layers could be as much as four or five feet at higher elevations and up to two feet deep at lower elevations. Tomorrow is a day to have a stepping back mindset and avoid steep avalanche terrain. Conservative decision making is the only way to navigate around this unique situation where, to varying degrees, weak snow layers can be found on all aspects and elevations.
