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
Several operators preformed explosive control on Sunday. Results were up to size 3.5 on various aspects in the alpine, some involving standing timber. One natural size 3.0 avalanche was reported from an east aspect at 2650 metres that failed on the mid-February layer and scoured down to the ground.
Snowpack Summary
Operators report that periods of broken skies on Sunday did not create widespread moist surface snow. It was reported to be warm enough to help settle the recent new snow and storm slab. The combined slab above the mid-february persistent weak layer is now between 150-200 cm. Some operators continue to get easy-moderate sudden planar character shears on the mid-february surface hoar in shallow areas. Snowpack conditions continue to be tricky to evaluate, and are variable throughout the region. Forecast strong wind and new snow may develop new windslabs in the alpine and at treeline.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.