Watch for conditions that change with elevation. Heavy rain at lower elevations means heavy snow up high.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
THURSDAY: 5-15 mm of precipitation with moderate southerly winds and freezing levels around 2000 m.FRIDAY: Unsettled conditions with isolated flurries, moderate becoming light southwesterly winds and freezing levels dropping to 1500 m.SATURDAY: A mix of sun and cloud with flurries possible late in the day, light winds and freezing levels around 1000 m.
Avalanche Summary
Reports from Tuesday include continued natural loose wet avalanche activity up to Size 2 on steep sun exposed slopes. A Size 2 natural storm slab and Size 1 skier triggered wind slab was also reported. On Monday a natural Size 2 wind slab was observed on a northeast aspect at 2100 m failing down 40 cm. Explosives triggered a few Size 2-3 persistent slabs failing on the early February weakness down 50-60 cm. Rain at lower elevations is expected to destabilize the upper snowpack resulting loose wet sluffing and potentially increasing the sensitivity of triggering persistent slab avalanches. In the alpine, touchy new wind slabs have the potential to step down and trigger persistent slab avalanches.
Snowpack Summary
Around 10 cm fresh snow has fallen at higher elevations accompanied by strong southerly winds, while elsewhere the snow surface has become wet, loose and cohesionless from rain and previous sun-exposure. Rapidly settling storm snow from last week is still bonding poorly to the previous snow surface from early February, which is now down 60-80 cm and includes a sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. Recent strong winds from the south and west had redistributed the recent storm snow in exposed terrain forming wind slabs. The mid and lower snowpack are generally well settled and stable in deeper snowpack areas but may be faceted and weaker in shallower areas. The mid-December surface hoar/facet persistent weakness can now be found down roughly 150 cm. This weak layer has become inactive in the south of the region, but may still be lingering in the northern part of the region near Blue River and Valemount. This layer is expected to get tested during the current period of sustained warming.
Problems
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.
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.
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.