Confidence
Fair - Intensity of incoming weather is uncertain on Friday
Weather Forecast
Overnight Thursday: Snow amounts 5-10cms. Ridgetop winds 30-40km/hr from the SE. Friday: Snow amounts 2-5cm. Ridgetop winds 20km/hr from the South. Freezing levels near 1800m. Saturday/Sunday: A ridge will persist through the weekend. Bringing mainly cloudy skies, and accumulations 2-5cms. Freezing levels near 1100m accompanied by moderate SW winds.
Avalanche Summary
On Wednesday natural cornice fall occurred. This large trigger pulled out a size 3 slab avalanche from the slope below. The avalanche occurred on a North aspect @ 1800m. The crown depth was up to 1.5 m, running 800m. No new avalanche activity was reported on Thursday.
Snowpack Summary
Recently, dribs and drabs of snow has fallen on a variety of surface forms. The bond of this new snow will need to be monitored as incremental loading may occur over the next week. The new snow sits on a variety of old surface snow conditions. They consist mainly of crusts that have developed due to melt/freeze conditions, and direct solar impact on steep Southerly aspects. Northerly aspects still host dry, wintery snow. On exposed lee slopes in the alpine there are pencil-4 finger stiff wind slabs. Surface faceting is occurring on sheltered, shady aspects. While shallow, rocky slopes are faceting and weaker; posing a threat to deeper releases. Surface hoar growth is 5-10mm at treeline, and below treeline. These may be our next layers of concern once buried. The Feb 01 (120201) rain crust is down 10-40 cm up to about 2000 meters. The mid-January crust is down between 50-100 cm, and the mid December crust is buried down up to 200 cm. The average snowpack depth at 1650m is near 240cm.
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.