A touchy storm slab is developing with continued light snowfall and moderate southerly winds. Danger will rise rapidly by Friday when we get hammered by a warm, pacific storm.
Weather Forecast
Today expect flurries, with accumulations up to 5cm. Moderate SW winds will continue to load lee slopes. Snowfall intensity will increase on Thursday, with up to 15cm of snow, gusty S'ly winds, and freezing levels rising to 1700m. Heavy snowfall is expected on Friday with up to 35cm of snow, and strong SW winds. Freezing levels rise to 1800m.
Snowpack Summary
30-50cm sits on the Jan 30 surface hoar/crust layer. Expect to find the Jan 30 crust up to 2200m. Snowpack tests indicate that the storm slab may bond poorly to the crust, which acts as a smooth bed surface. Jan 15 surface hoar layer is down 70-110cm and the December 17 is down 140-190 cm. Windloading will increase slab properties in lee areas.
Avalanche Summary
Yesterday, skiers accidentally triggered a size 2.5 avalanche from a SE aspect at 2120m. The avalanche propagated ~200m wide and ran up to 600m. Along the highway one size 3 and numerous size 2-2.5 natural avalanches were observed, occurring from all aspects generally above 1800m. Recent activity is occurring on the Jan 30 crust.
Problems
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.
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.