Tricky avalanche conditions require extensive experience to travel safely at and above treeline this weekend.
Confidence
Fair - Due to limited field observations
Weather Forecast
Friday: A cold front sweeps across the region Thursday night lingering into the first half of Friday bringing light precipitation & big winds out of the NW clocking in at 60 - 90 km/h. No significant precipitation is expected out of the system. Temps are forecasted to stay steady around -6 @ 1500m on Friday.Saturday: High pressure builds back into the region Saturday keeping the region dry through the weekend under scattered clouds. Freezing levels will stay near valley bottom but an inversion is forecasted for the area bringing above freezing temperatures between 1800m & 2300m Sunday & Monday.
Avalanche Summary
Numerous size 2 -2.5 avalanches have been reported failing both naturally & with the aid of explosives on high elevation north through east facing slopes.
Snowpack Summary
Snow depths are variable throughout the region. In the alpine there is 170- 250cm. At treeline depths vary from 130-150cm. Sunday's warm, moist storm combined with strong southwesterly winds created stiff wind slabs on north through east facing slopes. Winds shifted to the North Wednesday creating a reverse load. Now there are a wide variety of windslabs at and above treeline on all aspects.Conditions are primed for human triggered avalanches at and above treeline due to weak sugary snow at the ground combined with tricky wind slabs. The upper snowpack is tightening up forming a stronger mid-pack, but if an avalanche is triggered in the upper layers or initiated from a shallower spot in the snowpack it could step down to weak basal facets at the ground creating large and unmanageable avalanches with very high consequences.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.