Friday is expected to be warm. Avoid exposing yourself to large, sun-baked terrain. Check out the conditions video at http://bit.ly/1EAQd9O
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Friday
Weather Forecast
It’s expected to be dry and very warm (freezing level 3000 m) on Friday. Around 5-10 mm precipitation is expected on Saturday, followed by a further 10 mm or more on Sunday. The freezing level during the precip is around 2200 m, falling to around 1500 m on Sunday, although there is a fair bit of uncertainty about what type of precip we will receive (rain or snow). Winds are moderate to strong from the SW.
Avalanche Summary
On Tuesday, our field team members in the north Elk Valley experienced several whumpfs on south facing treed terrain at 2200 m. They also experienced a whumpf of a hard slab near ridge top at 2450 m and saw a deep slab release on a sunny aspect that probably occurred some time in the last week. Recent loose wet avalanches up to size 1.5 appeared to have been triggered by solar warming. On Sunday, a skier-triggered slab released on a weak layer near the ground in Kananaskis Country. As temperatures remain very warm for the next few days, it might be time for a mentality shift. Treat the snowpack with more caution than in recent weeks. Large avalanches are becoming more likely again.
Snowpack Summary
Any available snow may be shifted by SW winds into wind slabs at high elevations. Lower down the mountain, the snowpack has become warm and weak. The most prominent snowpack feature is a thick supportive crust 10-30cm below the surface. It extends up to around 2200m elevation. This crust has begun to break down in response to warm temperatures, and may not be providing the capping support it once was. Persistent weak layers still react in snowpack tests and could wake up with continued warming.
Problems
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.
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.
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.