Snow and strong winds have formed wind slabs in alpine lee areas and exposed treeline features. These slabs may be poorly bonded to the underlying crust. Watch for sluffing in steep terrain and loose, wet releases on sunny and low elevation slopes.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
TONIGHT: Mostly cloudy, flurries. Accumulation 2-4 cm. Ridge wind light to moderate, south. Alpine temperature near -6. Freezing level 500 m.SUNDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light, east. Alpine temperature near -5. Freezing level 1700 m.MONDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light to moderate, east. Alpine temperature near -3. Freezing level 1900 m.TUESDAY: Mostly cloudy, light flurries. Accumulation 2-8 cm. Ridge wind light, northwest. Alpine temperature near -6. Freezing level 1500 m.
Avalanche Summary
Friday there was a report of a natural cornice collapse that produced a size 3 deep, persistent slab avalanche that failed on an early-season layer (300 cm deep) on a northeast aspect at 2600 m. Several loose, wet releases up to size 2.5, running to ground in low elevation paths were also reported on Friday.Wednesday there was a report of natural cornice failure that resulted in a size 2.5 wind slab release on a northeast aspect at 2700 m, while a skier was able to trigger a size 2 wind slab (40 cm deep and 100 m wide) on a recently buried crust on a similar aspect at 2400 m. There was also a report of a remotely triggered (from a distance) size 1 wind slab in an east-facing gully at 2300 m.On Tuesday a natural size 2.5 cornice failure on a north facing alpine feature did not produce any additional avalanche activity when it impacted the steep slope below. A natural size 2.5 wind slab was also observed on a cross-loaded east facing feature at 2400 m.On Monday steep solar aspects produced natural loose wet avalanches to size 2 between 2000 and 2600 m. A size 3 natural cornice failure was also reported from a north facing slope at 2600 m.
Snowpack Summary
A dusting of new snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects), while 20-40 cm of storm snow can be found at higher elevations. There are now a few different crusts in the upper 50 cm of the snowpack, with only the upper, most-recently buried crust posing a concern with the recent storm snow.There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 60 to 140 cm below the surface. This buried crust/surface hoar interface was widely but has not produced any avalanche activity in the past week. It is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or a cornice collapse).Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.