Wind slabs have gained enough cohesion to be a real concern for human triggering. Manage exposure to steep solar aspects when sun shines and temperatures rise.
Weather Forecast
A slight temperature inversion is at play this morning with cooler air in the valley bottoms. A ridge of high pressure continues to block all precipitation. Expect mostly sun with cloudy periods, light NW winds, and freezing levels rising to 1200m. The high pressure system weakens Tuesday, allowing a weak low pressure system to move over the area.
Snowpack Summary
Below 1900m a light dusting of new snow sits on a bulletproof crust. Up to 2200m 15-20cm of light snow sits on the Feb 18 crust/ surface hoar layer. The Feb 14 crust is down 20-25 and is up to 10cm thick. Soft wind slabs on all aspects have formed in exposed areas at treeline and above. Persistent weak layers down 1-1.5m are stubborn to trigger.
Avalanche Summary
No new avalanches were observed yesterday in the highway corridor. A field team on Mt Fidelity observed cracking in pockets of soft wind slab at treeline. Reports of small skier controlled avalanches on wind loaded pockets near ridgeline.
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.