Human triggered avalanches remain possible today, especially in steep, rocky, wind exposed areas at the middle and upper elevations. Buried crust-facet combinations lurk on NE through E through S slopes, though their strength should continue improve after today's warm up and refreeze. Moniter the effects of the sun on the snow surface today and minimize exposure time on steep sunlit slopes.
Fresh wind slabs that are up to a foot thick are located above treeline in the lee of southerly winds. Stubborn wind slabs that are 1-2 feet deep linger in the alpine. Pay attention to signs of instability such as cracking within wind drifted snow.
Avalanches could occur on both the 3/29 and 3/20 interface, but will trend towards unlikely as crust development occurs. The 3/29 interface is 1-2 feet below the surface of the snow and the 3/20 interface is 2-3 feet below the surface of the snow (slightly deeper if in wind loaded terrain). Both layers are buried within the top meter of the snowpack and are reacting in the medium to hard range in stabily tests, with a mix of propagating vs. non-propagating results.
Snowmobile triggered wind slab avalanche that failed on the 3/29 interface, as viewed from Pyramid. 20230405-SS-AMu-R2-D2-I East facing B-Z Bowl @ 9,200'.
Wet loose avalanches will continue to be a concern at the middle and lower elevations today as the spring warm up continues. Look for signs of instability such as roller balls on sunlit slopes.
Low elevations began showing signs of Wet Loose activity Tuesday afternoon.
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.
