Front Range
Avalanchemarkus beck (pro-avy 2) · Feb 15, 2017 · Front Range
Weather
Since Tue, the weather is showing strong diurnal characteristics which also manifests itself on sunny vs shady slopes. This will be going on through Thu at least. This morning, a cold clear night gave way to sunny skies. Mid afternoon isolated cirrus clouds showed up. Min. temps around 20F (morning and evening) with a high around 30F at 11,500ft. Radiation felt moderate+ on sunny aspects, lighter on shaded aspects. Temps in the alpine remained cool on all aspects. Calm to light winds at lower elevations, becoming moderate towards and at ridgetops out of the WNW; isolated and light blosno. Westerly fetch zones in the alpine are mostly devoid of snow.
Snowpack
While the snowpack is highly variable in the ALPINE (windward slopes are eroded to the ground or are full of zastrugis, leeward slopes hold good snow with generally hard slab topped by spotty shallow creamy powder, observed basal depth hoar), the spx is much less variable over space around and below treeline. AROUND TREELINE the snowpack is much less wind affected but shows great differences between sunny and shady slopes: 1) The heat on the SUNNY ASPECTS has strengthened the snowpack. Snow profiles consistently show an overall strong spx with a pointedly low TG; facets throughout the spx show clear signs of rounding. There is a very stout midpack at 1F to P hardness. Steeper slopes had multiple P and K hard mf-crusts associated with significant faceting, though these seem unreactive in hand and ski tests. Despite a cool very light surface breeze, we observed widespread moist snow near and at the snow surface by noon (especially with increasing slope steepness) and even percolation columns and occasional small water pooling. By mid/late afternoon, breakable mf-crusts developed on the surface on SE-SW. Development of surface hoar and near-surface faceting was evident in the morning but warm temps and radiation caused these facets to melt by the afternoon. 2) SHADED SLOPES show a more pronounced layered spx structure. Observed widespread but small surface hoar and near-surface faceting in wind sheltered areas that remained intact throughout the day. In wind protected open glades we found buried surface hoar in several snowpits 20-40cm down, resting on a 1F to P mid pack of rounded facets. This layer produced non-conclusive results in our tests: CTM-Q1 but ECTX or planar resistant, yellow flag count 4-5, no instability signs observed but isolated reports of avalanches throughout this and neighboring zones over the past week demonstrate that this problem, albeit very spotty, must not be taken lightly . We theorize that the overlaying slab in our test sites was too soft (ranging from F to 1F/4F) and too shallow for propagation to occur. We observed basal depth hoar with an avg. layer thickness of 50cm, showing signs of rounding but at and very near the ground, 2-3mm depth hoar facets were still intact. Nevertheless, with an avg. HS of 150cm around treeline, rounding depth hoar in an ongoing low TG and no activity, it seems very unlikely that avalanches would release on basal depth hoar. BELOW TREELINE, the snowpack appears well settled on all aspects, with fair to poor riding quality except on shady slopes.
Avalanche
We determined the main avy problem in the ALPINE to be persistent slab, exaggerated by old and recent windslab. Skier triggered shallow slabs are possible in recent wind drifts. The deeper instabilities are unlikely to be triggered but would be larger and should not be ruled out in very steep leeward terrain features - most likely trigger points would be below cornices, around cliff bands, areas where couloirs open up into broader slopes and areas where the hard slab is shallow. We rated stability here as good/very good, danger at Moderate. AROUND TREELINE, we determined the avy problem to be of diurnal nature: 1) SUNNY ASPECTS - We did not observe any avalanche activity nor instability signs other than isolated and minor roller balling and small pin wheeling on very steep slopes originating from rocks and trees, also expecting small loose wet avalanches by noon in very steep terrain especially from rocks/cliffs. Large cornices would also be suspect. We rated stability here as good, danger at Low. 2) SHADY ASPECTS - Structural evidence of a weakness caused by very spotty buried surface hoar about 0.5-1.5ft down, but non-conclusive tests nevertheless are cause of some concern. Without digging, it is impossible to determine if this weakness exists. Best strategy is to treat very carefully or even avoid terrain >35 that is conducive to producing surface hoar (wind sheltered open glades on N-E, especially with evidence of recent or old wind loading). We rate the stability here as good, danger at Moderate. BELOW TREELINE, we rated the stability as very good, danger at Low. Wet loose avalanches on very steep terrain in conjunction to terrain traps on sunny slopes, or small persistent slabs on very steep terrain on buried surface hoar may pose a threat.