Avalanche Forecast
Issued: Nov 27th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Loose Wet.
wlewis,
Avalanche Canada
High danger returns with wet snow, rain and extreme winds. Large natural avalanches are expected Sunday. Minimize your exposure to avalanche terrain and overhead hazard.
Summary
Confidence
Weather Forecast
SATURDAY NIGHT: 5-10cm of snow is expected over late afternoon with freezing levels below 1000m. The storm intensifies through the night. Winds increase to strong and extreme from the southwest as freezing levels soar above 2000m for most areas. 10-30cm of snow is forecast above, and mixed precipitation or rain below.
SUNDAY: Moderate to heavy precipitation throughout the day will deliver 10-30mm with freezing levels may dip below 2000m. Strong west-southwest winds decrease to moderate overnight.
MONDAY: We will see another short-lived break in the storm. Light accumulations are expected. Freezing levels sit above 1500m with strong westerlies.
TUESDAY: Yet another atmospheric river (moisture heavy weather system) hits the coast and begins to affect the interior. Moderate accumulations, strong winds and high freezing levels return.
Avalanche Summary
On Friday November 26, size 2 natural storm slabs were reported in wind loaded lee features in the alpine. Multiple size 1 and 1.5 avalanches were triggered by explosives and skiers near Revelstoke.
The Mountain Information Network received several reports of reactive storm snow. Whumpfing and cracking within the storm snow was seen on low and steep angle terrain, at treeline and above. One report in the Kokanee Range also noted significant variability in wind loading from northerly and southerly winds.
Glacier National Park saw a second day of a natural storm slab avalanche cycle up to size 3, initiating in alpine features. Explosives also produced avalanches up to size 3 in the same area on Thursday, running full paths to valley bottom.
A report on the Mountain Information Network from Rogers Pass reported a size 2.5 natural avalanche running to valley bottom on Friday. Again, reports noted shooting cracks within the storm snow on steep and low angle slopes, and small remotely triggered slabs.
Snowpack Summary
20-40cm of wind effected storm snow or rain from Saturday night will fall on 40-90cm of settling snow that has been redistributed by south and southwest winds at treeline and alpine elevations. In some areas a rain crust may exist between the old and new storm snow.
The mid November crust is up to 5cm thick and found down 50-120cm with faceting below the crust. The lower snowpack contains several early season crusts which appear well bonded.
Snowpack depths exceed 300cm at treeline and alpine elevations, while below 1600m depth decreases rapidly.
Terrain and Travel
- Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
- A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
- Be alert to conditions that change with elevation and wind exposure.
- Avoid exposure to overhead avalanche terrain during periods of heavy loading from new snow, wind or rain.
Problems
Storm Slabs
A fresh storm slab will build over Saturday night and into Sunday. Expect widespread storm slab conditions with strong southwest winds creating deeper and more reactive deposits in wind effected features.
Travelling in avalanche terrain is not recommended as large natural and skier triggered avalanches are expected with wide propagation.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
As freezing levels rise above 2000m recent storm snow will be hit with mixed precipitation or rain. Wet snow or rain will rapidly reduce weaken the upper snowpack. Likelihood will increase throughout the day as rain saturates the snowpack.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Nov 28th, 2021 4:00PM
