The wind is expected to be strong from the southwest. If there is more snow than the forecast 10cm available to be transported into windslabs, then the Alpine danger level may be closer to HIGH.
Confidence
Fair - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
A Pacific frontal system should move on to the coast this afternoon or evening. The front is forecast to be fast moving and should affect the interior ranges overnight Monday. Forecast snowfall amounts are 5-10 cm overnight combined with strong southerly winds. The wind is expected to shift a bit to the southwest and continue to be strong during the day on Tuesday as another 5-10 cm is expected to accumulate. Unsettled weather is forecast for the interior mountains on Wednesday as the fast moving system should have moved on to the East. On Thursday a weak low pressure system is expected to move up from south of the U.S. border spreading light to moderate precipitation mostly to the southern regions of the interior.
Avalanche Summary
Natural avalanches up to size 3.5 on northerly aspects failing down about 100-150 cm on the mid-february persistent weak layer. Avalanches releasing on this layer are becoming less frequent. Large triggers like cornice fall may initiate a release on the PWL.
Snowpack Summary
Sunny breaks on Sunday caused moist snow up to about 2400 metres on solar aspects and up to about 1500 metres on all aspects. The recent storm snow is reported to have settled and bonded in most areas. Recent cornice growth has made cornices unstable. The new snow has added to the well consolidated storm slab that overlies weak surfaces that formed early February. This interface, which lies between 1 and 2 metres below the surface, includes a widespread surface hoar instability that, depending on aspect and elevation, may exist in combination with facets or crusts. These persistent weak layers have been reactive all week and remain a concern at all elevations. The weight of new snow, near-surface avalanches, sleds, and skiers may easily trigger these deeper weaknesses creating unexpectedly 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.