A good time to be conservative as a storm threatens to tip the balance on the persistent weak layer. After the storm, watch for a temperature inversion Wednesday that may keep hazard elevated especially if combined with strong winds.
Weather Forecast
15cm, rising temperatures, and gusty alpine winds are expected with the passage of a warm front tonight. Tuesday morning as the cold front passes, expect winds to peak, temperatures to drop, and the precip to trail off. Watch out Wednesday for a strong inversion with freezing levels reaching 3000m and some potential for Strong West winds.
Snowpack Summary
160 to 200cm now at treeline. 30cm of snow accumulated since Friday now forms a very soft storm slab above faceted and wind affected surfaces. Cold temperatures slowed settlement in the 50 to 90 cm slab above the Dec 13 Crust/Facet and Dec 16 Surface Hoar layers. This has also promoted facet development above the crust and weakened this layer.
Avalanche Summary
Monday I triggered a south facing 40 degree slope at treeline by taking off my skis to dig a profile at the top of the start zone. Thankfully, only a 10cm crack formed at the crown in front of my feet, however cracks could be seen up to 50m away down the slope. Subsequent tests produced easy sudden planar shears on facets above the Dec 13 Crust.
Confidence
Freezing levels are uncertain on Wednesday
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.