Avalanche Forecast
Issued: Jan 12th, 2019 4:28PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
ghelgeson,
Avalanche Canada
A big rise in freezing levels may mean that a deep persistent slab wakes up. A lot of uncertainty exists as to what this layer will do as temperatures climb. High levels of uncertainty are best managed by choosing conservative terrain.
Summary
Confidence
Low - Freezing levels are uncertain
Weather Forecast
A classic temperature inversion sets up Saturday night which will likely stick with us until Tuesday. No significant precipitation is expected until possibly Friday.SATURDAY NIGHT: Temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1900 and 3000 m, light to moderate west/southwest wind, no significant precipitation expected.SUNDAY: A few clouds, temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1900 and 3000 m, light southwest wind at most elevations with moderate west/northwest wind at ridgetop, no significant precipitation expected.MONDAY: Clear skies, temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1500 and 3000 m, light variable wind, no significant precipitation expected.TUESDAY: A few clouds, freezing level at valley bottom, light variable wind, no significant precipitation expected.
Avalanche Summary
On Friday natural avalanches size 1.5 to 2 were reported from northeast through northwest facing terrain at and above treeline. Control work produced storm slab avalanches to size 2.5 on similar aspects. Control work also caused cornices to fail on southeast facing terrain which subsequently produced storm slab avalanches to size 1.5.Numerous storm and wind slab avalanches were observed in the region on Thursday. Most of them were small (size 1 to 1.5), between 1600 m and 2300 m, and on all aspects. They were triggered naturally, by skiers, and explosives.For the weekend, the likelihood of triggering storm slabs may increase due to the substantial amount of warming expected around upper below treeline, treeline, and alpine elevations. The likelihood of triggering deeper weak layers may also increase too. Watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest. See here for an example.
Snowpack Summary
Warm upper-level air temperatures may be impacting the snow surface. You may find dry snow, moist snow, or possibly a frozen melt-freeze crust, depending on how warm the air temperatures are. The warm air may produce touchy storm slabs at all elevations. At the highest of elevations, wind slabs may still linger in lee and cross-loaded terrain features.The middle and lower portions of the snowpack are generally well-settled and strong. However, there still remain a few deeper weaknesses in the snowpack around treeline and alpine elevations. Professionals are still tracking a layer around 150 to 200 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack may also still be composed of weak faceted grains. The likelihood of triggering these layers may increase with the warm air incoming this weekend. These layers would most likely be triggered by humans in areas where the snowpack is shallow.
Problems
Storm Slabs
Up to 30 cm of recent snow has formed a storm slab which may become more reactive with rising temperatures and sun affecting the snow, especially in wind loaded areas.
Extra caution needed around cornices with current conditions.Be cautious as you transition into wind affected terrain.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A deeply buried weak layer may wake up with rising freezing levels and sun affecting the snowpack . Large triggers like cornices may cause avalanches on this layer, and cornice failures become more likely during warm, sunny conditions.
Pay attention to overhead hazards like cornices which easily trigger the deep persistent slab.Minimize exposure to steep slopes on warm or sunny days.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 13th, 2019 2:00PM
