Wind slabs continue to surprise riders up at higher elevations. Use terrain features to your advantage while avoiding wind loaded pockets, and unsupported roll-overs.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Tuesday
Weather Forecast
There is significant disagreement between forecast models - local snowfall amounts may be higher than predicted. Wind and precipitation start to kick in on Monday, before ramping up on Tuesday.MONDAY: Cloudy with flurries bringing up to 5-10 cm of new snow, increasing overnight. Moderate southwest winds 20-40 Km/hr. Freezing level 1400 metres with alpine high temperatures of -5.TUESDAY: Snow (10-25cm). Moderate to strong west winds, Freezing level to 1700 metres with alpine high temperatures around -4. WEDNESDAY: Sunny with cloudy breaks and isolated convective flurries. Moderate northwest winds 20-45 Km/hr. Freezing level to 1400 metres with alpine high temperatures around -5.
Avalanche Summary
On Saturday we received reports of several wind slabs and storm slabs to size 2.5, mostly on northerly aspects above 2200m. Also on Saturday, a wet loose size 1.5 avalanche injured a skier in Glacier National Park on a west aspect near 2000m.On Saturday, a size 1.5 natural cornice fall was reported on a north west ridge line near 2400m, pulling out a small soft slab below.On Friday we received widespread reports of several size 1-2 wind slab and storm slab releases. These were skier triggered, ski cut, and explosives triggered. They occurred on primarily north/east aspects at treeline and above.
Snowpack Summary
Convective snowfall coupled with strong to extreme southerly winds brought a wind-affected 15-25 cm of new snow since Thursday night. The new snow has buried a couple of recent layers of storm snow that are separated by temperature and sun crusts at lower elevations and on south aspects. Surface hoar layers have been reported between these storm snow layers on shaded aspects at higher elevations and can likely now be found at approximately 30 and 50 cm below the surface. Some potential exists for shallower slab avalanches to 'step down' to these deeper layers.New snow amounts taper with elevation and below 1900 m, reduced accumulations have buried a supportive crust on all aspects. Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with a surface avalanche stepping down, large cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.
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.