Vail & Summit County
AvalancheAnonymous · Feb 4, 2014 · Vail & Summit County
Weather
Started out sunny with broken skies becoming S-1 later in the day. Temps were cold all day. Lower elevations had calm to light winds while higher up especially at ridge lines light to moderate NW winds caused moderate blosno and nippy wind chills.
Snowpack
Surprisingly, the storm snow still blankets most of the mountains, only in the alpine are there clear signs of recent winds redistributing the snow onto leeward slopes. This storm snow camouflages the old snow surface and with it clues about old wind and persistent slabs. The recently drifted snow has formed shallow wind slabs (up to 1-2ft) and many such terrain features on E'ly slopes 35dgr+ have avalanched; no stepping down into the [deep] persistent layers observed. On N-E, the snowpack structure is 1-2ft storm slab (F to 4F though settling a bit), 0.5-4ft of old snow (1F to P), 1-3ft of depth hoar (4F to F) - the snow surface in wind exposed spots had a wind crust up to several inches thick (4F to 1F). Instability tests around treeline on N-S showed easy to moderate Q1 fractures and eager propagation (RB4, ECT13) on a faceted 1-2" layer of buried nsf and sfc facets (4F-F) between the storm slab and the old snow. On S'ly slopes, 1-2 mf crusts in the mid pack have started to facet and produced several rumbling collapses and shooting cracks up to 50meters; the fracture occurred just under the crust in a 1-4" layer of facets (4F-F). Instability tests demonstrated that the snowpack consisting at least 1 crust is easy to fracture with high propagation potential. Several instability tests targeting the deep persistent layers near the ground revealed very easy fractures and very high propagation potential (several ECT's released upon isolation, DT's all less than 10 hits with Q1). Stability below treeline, especially on S, is fair to good, but stability around and above treeline is poor on all aspects where the snow depth exceeds 3-4ft. Fair to say the snowpack is near its tipping point of strength vs stress and the recent avalanche activity (small wind slabs, large persistent slabs) would support that. The upcoming snowy week with its grand finale over next weekend may very well push the snowpack into another avalanche cycle.
Avalanche
Several wind slabs on E'ly all elevations, several persistent slabs N-E-S around and above treeline. Most slopes 35dgr+ around and above treeline did slide during the last avalanche cycle a couple of weeks ago. Some start zones have refilled completely (at times further down during the sustained wind event a while back) though many have still not - this is not always easily detectable (especially where the wind loading occurred further down than usual) but stability seems much higher on such slopes.