Regions
Northwest Inland.
Lurking persistent weaknesses and mild spring-like weather make me reluctant to drop avalanche danger any lower. Continue to approach large alpine slopes with caution, especially with cornices perched above.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
SATURDAY: Increasing cloud. The freezing level is around 1100-1300 m. Winds should be moderate from the SW-SE. SUNDAY: Cloudy with a chance of flurries. The freezing level is near 1200 m and winds are light to moderate from the southeast. MONDAY: Cloudy with light snow. The freezing level is around 1200 m and winds are light from the east.
Avalanche Summary
On Thursday there were reports of loose wet sluffs up to size 1.5 on solar aspects in the afternoon. A larger loose wet cycle with wind slab activity (to size 2.5) was observed in the previous 24 hours. In the far north of the region, natural cornice falls continue to trigger size 2-3.5 persistent slab avalanches, primarily on north-facing alpine slopes.
Snowpack Summary
In sheltered areas at higher elevations, 20-30cm of low density facetting snow can be found. Recent southerly winds have redistributed the surface snow in exposed terrain formed wind slabs and cornices in leeward terrain. South facing slopes could be capped a sun crust or moist snow depending on the time of day. A layer of surface hoar from early March can be found down 60-80cm but only seems to be a problem for the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February which can be found down about 1m or more. These layers have been dormant for a couple weeks but could wake up with heavy storm loading, substantial warming, or a heavy trigger like a cornice fall. In the far north of the region, there is an isolated weakness at the base of the snowpack that has been responsible for some very large and destructive avalanches.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.