A significant winter storm is heading our way today and will increase the Avalanche Hazard over the next few days. Expect Artillery Avalanche Control and Highway closures on Thursday.
Weather Forecast
A significant storm system will arrive today and persist until Friday evening with a forecasted snowfall amount of 80cm with moderate to strong winds. Today we will see ~10cm of snow, an alpine high of -7 and 30kph Southerly winds. Snowfall amounts are forecasted to be; 20cm tonight, 30cm tomorrow, 20cm Friday... Wahoo!
Snowpack Summary
40cm of storm snow has been redistributed by moderate southerly winds. The Dec 9 and Nov 21 interfaces are down ~120-160cm and still producing hard/sudden test results, and can be triggered in shallow/rocky areas. The mid to lower snowpack is generally well settled and rounding. Decomposing early seasons crusts are still present at/near the ground.
Avalanche Summary
A skier triggered size 3 avalanche from Bruins Ridge nearly swept 2 skiers over cliffs into 8812 Bowl on Sunday. A field team found the avalanche slid on the Nov 21 sun crust, triggered from a shallow area. The crown ranged from 30-150cm in thickness, 40m wide, and 300m in length. No new avalanches observations or reports yesterday.
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.