"The green light is off." Unusually warm conditions with periods of strong sun and periods of rain have weakened the upper snowpack. Avoid sun-exposed slopes on Friday afternoon.Check out our blog on the current warm conditions: http://goo.gl/nS6uhF
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A ridge of high pressure should bring a mix of sun and cloud for Friday. Freezing levels are expected to reach around 2500m and alpine winds are forecast to be strong from SW by the end of the day. On Saturday, a weak storm system reaches the region. Models are currently showing 5-15mm between Saturday morning and Sunday morning. Freezing levels on Saturday are expected to stay around 2000m during the day but are forecast to fall to below 1000m by Sunday morning meaning rain may switch to snow at many elevations. During the storm, alpine winds are forecast to be strong from the SW. On Sunday, the storm should exit and a mix of sun and cloud can be expected with light winds.
Avalanche Summary
On Thursday, a natural cornice failure triggered a wind slab on the slope below. On Tuesday, loose wet avalanches and cornice failures from steep sun exposed slopes were reported. There have been some concerning avalanches in the neighboring Columbia regions including natural slabs releasing to ground and reactive wind slabs over facets being remotely triggered. On Friday, sunny and warm conditions are expected to destabilize the snowpack. Large avalanches have isolated potential to release on deep weak layers. Sluffing is expected from steep sun-exposed slopes and the triggering of wind slabs is possible in the alpine.
Snowpack Summary
A moist snow surface is being reported to around 2500m on solar aspects and 1800m on north aspects. Wind slabs are being reported in the alpine and may be overlying the early-March crust/facet layer. The late-Jan crust/surface hoar layer can be found about a metre below the surface in deeper snowpack areas. The mid-January surface hoar can be found below that. These layers have gained significant strength and have been dormant for several weeks but have the potential to wake-up with the current warm temperatures.
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.
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.
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.