Incoming weather combined with a complex snowpack means this is no time to be pushing into steep terrain. Conservative slope selection is critical to safe mountain travel.
Confidence
Poor - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
Overview: A pacific frontal system will push inland on Saturday bringing moisture to the interior until early Monday morning. Expect a ridge of high pressure to develop for Monday and Tuesday. Due to significant weather model disagreement for Saturday night and Sunday, I have limited confidence in forecast snowfall amounts and freezing levels.Overnight Saturday: Light to moderate snowfall / Moderate westerly winds with strong gusts / Freezing levels between 1500m-2000mSunday: Moderate to locally heavy (western slopes) snowfall / Moderate westerly winds with extreme gusts) / Freezing level at about 1600mMonday: Light flurries with a mix of sun and cloud / Moderate westerly winds with strong gusts / Freezing level at 1500mTuesday: Mainly sunny skies / Light northwest winds / Freezing level at about 1200m
Avalanche Summary
Expect fresh wind slab and loose dry snow avalanche activity to increase throughout the forecast period as snow flurries load exposed alpine and treeline feature. At treeline elevations and below, significant warming has made large persistent slab avalanches are highly sensitive to human triggers. In parts of the forecast area, very large destructive avalanches running to valley bottoms from major start zones remain a concern. Neighboring forecast regions have recently reported large avalanches initiating in the new storm snow, then stepping down to deeper layers, some running full path to the ground. Cornice failures triggering large deep persistent avalanches have also been reported.
Snowpack Summary
Convective flurry activity has already accumulated 10-15cm of fresh snow in some drainages, which has likely blown into touchy wind slabs on leeward slopes. These recent accumulations overlie crusts on previously sun-exposed slopes and surface hoar in shaded terrain. More snow and wind forecast for Saturday night will add to this developing storm slab. Below the new snow 50-70 cm of settled snow has been bonding poorly to buried surface hoar and crusts. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been highly variable in terms of reactivity and is very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.