Human triggered avalanches remain possible at ALL ELEVATIONS. Slopes where wind affected snow overlies buried weak layers are of primary concern. Steep and rocky terrain near ridglines and summits likely harbors weak snow near the bottom of the snowpack and wind affected snow on top. Moniter the effects of the sun on the snow surface today and limit exposure time on steep sunlit slopes. Pay attention to signs of instability such as audible collapsing of the snowpack and cracking within wind affected snow.
Today warm temperatures and sunshine could cause small wet loose avalanches to form on south facign terrain at the lower elevations on Togwotee Pass. Look for signs of instability such as roller balls and tree bombs.
Layers of weak snow exist within the top meter of the snowpack and deeper. The most recent snow lies on top of multiple crust/facet combinations that formed in March and February. Thes layers have been recently reactive on Angle Mountain and Mt. Leidy. Triggering a 2-3+' thick persistent slab avalanche still remains a possibility. You're most likely to trigger a slide involving this weak snow on or adjacent to very steep slopes (steeper than about 35 degrees) where the wind has built slabs in recent days and weeks.
Deeper weak layers formed earlier in the season composed of crusts, facets, and depth hoar remain a concern. Triggering a wind slab or persistent slab on the March 20th interface could step down to these layers resulting in a large to very large avalanche.
Recent size D2 Avalanche on Angle Mountain
Stubborn wind slabs that are around a 1 foot thick linger throughout the forecast area. Easterly winds earlier in the weak helped to form cohesive slabs of snow in unsual locations. Look for wind rippled snow surfaces and pay attention to signs of instability such as cracking within wind drifted snow.
Spring warm up continues today, with above freezing temperatures expected from the valley floor to the highest peaks. A very weak system moves through today, bringing the possibility of snow showers in the mountains and rain/snow mix in the interior valleys. Wind slabs are prevalent in the alpine and their sensitivity to triggers could increase with solar input.
Recent avalanche activity was observed in the northern portion of GTNP yesterday. Forecaster Catino observed lots of wet loose activity shedding off of steep faces and an impressive avalanche that ran to the valley floor on a south aspect (likely ran during the last storm). Avalanche activity was observed in Avalanche Canyon two days ago, mostly wind slabs that were size 1.5 or less.
Have left the 3/20 and 3/29 persistent slab problems in place for now, but sensitivity is expected to go down after the peak heating today and subsequent refreeze tonight. The 3/29 interface seems to be more of an issue where it is presenting as a crust, northerly aspects do not seem to be as concerning as easterlies and southerlies. The same cannot be said of the 3/20 interface where it is a layer of NSF on NNE aspects.
