Confidence
Fair - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
Friday shows a lull between systems. The Interior will be mainly dry, especially further south. By Saturday another pacific frontal system will spread light-moderate amounts of precipitation accompanied by strong westerly ridgetop winds. Friday: Cloudy with snow amounts 3-5 cm. Alpine temperatures near -9. Ridgetop winds strong from the West. Saturday: Cloudy with snow amounts 5-10 cm. Alpine temperatures -8. Ridgetop winds strong from the West.Sunday: Cloudy with snow amounts near 10 cm. Alpine temperatures -7. Ridgetop winds moderate from the SW.
Avalanche Summary
No recent avalanche activity has been reported. On Tuesday, a wind slab avalanche size 1.5 was easily triggered under the weight of a rider from a NE aspects. Cross-loaded features and the immediate leeward side of ridge crests are likely touchy. Loose dry surface sluffing from steeper terrain is expected, use caution near terrain traps like cliffs, and depressions.
Snowpack Summary
Shifting winds have formed stiff wind slabs on the lee side of ridge lines.Snowpack depths at treeline vary across the region, averaging 70-110 cm. Incremental snowfall amounts are burying surface hoar and a faceted upper snowpack. In the Southern part of the region there is 40-70cm of low density snow sits over the late-November surface hoar/ crust/ facet interface. This layer may become reactive with additional load, and warming temperatures, forming more of a slab.In the Northern part of the region the lower/mid snowpack is weak, composed of an early season crust (more prevalent on north aspects) weak faceted crystals and depth hoar above and below the crust. This persistent slab may be stubborn to trigger, but if triggered have 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.