Avalanche Forecast
Issued: Dec 4th, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
cmortenson,
Avalanche Canada
Enjoy the sun & seek out sheltered northerly terrain for the best conditions. Watch for heat and sun creating wet snow on steep solar slopes and minimize overheard hazard in the heat of the day. Assess for wind slabs before entering steep slopes or wind-affected terrain.
Summary
Confidence
Weather Forecast
A temperature inversion continues for another day or two with a mix of sun and warm temps (up high) and cooler temps with valley fog and broken skies (down low). Alpine temperatures are forecast to reach +3 to +8 from 1800m to 3000m before the temperature inversion begins to break down Sunday.
FRIDAY NIGHT: An alpine temperature inversion persists overnight, but with clear skies in the alpine temperatures should dip below zero. Valleys will be much cooler with fog and temperatures near-5C. Winds will ease to light to moderate North/North-Westerly. Along the divide and to the east winds are forecast to be moderate to strong Westerly. No precipitation expected.
SATURDAY: Above freezing temperatures in the alpine (+3 to +8C) with mild valley temperatures to +1C. Winds will be light and variable in the morning and increase during the day to moderate Southwesterly. Along the divide winds will be moderate to strong Westerly. East of the divide warm temperatures are forecast at all elevations. No precipitation expected.
SUNDAY: A mix of sun and clouds as the temperature inversion weakens. Increasing moderate Southwesterly winds. Along the divide winds are forecast to be strong to extreme Westerly. No notable precipitation expected but isolated flurries possible later in the day.
MONDAY Mostly cloudy with sun breaks and more typical alpine temperatures of -3C. Winds are forecast to be moderate to strong SouthWesterly and strong to extreme Westerly across the divide. Scattered snow flurries with trace accumulations.
(New snow starts to look promising for mid week!)
Avalanche Summary
Cool overnight temperatures and winds are helping the snowpack to remain cool in spite of multiple days where alpine temps rose above zero temperatures. Highest alpine temperatures were experienced on Wednesday (+5 to 10C), and were lower on Thursday (+1-+3C) and Friday (+1 to +5C). Alpine temperatures are forecast to rise to +2 to +8C on Saturday before slowly returning to seasonal patterns by Monday.
Avalanche activity as been mostly isolated to predictable small to medium (up to size 1.5) loose wet avalanches on steep solar slopes or from extreme rocky terrain. Reports from adjacent regions were limited to pinwheeling, small to medium loose wet slides (to size 1.5) from steep solar terrain, and isolated small slab avalanches with explosives.
Concern remains for the above freezing temperatures in the alpine on steep solar aspects and windslabs on northerly terrain. Temperatures are not forecast to dip as low Friday night as they did Thursday night, diminishing the overnight recovery ahead of the peak alpine temperatures of +5 to +8 on Saturday.
Observations are limited right now, but there have been no reports of recent large avalanches. We appreciate the recent reports submitted to the Mountain Information Network. Keep them coming!
Snowpack Summary
Alpine and exposed ridge crests have been heavily affected by recent winds. Softish snow can still be found in sheltered northerly facing terrain where surface faceting has softened old wind slabs and no sun crusts are present.
Westerly and Southwesterly winds have scoured upwind slopes and ridges to ground or old crusts & redistributed snow into windslabs on cross-loaded galleys and lee-slope features. These old windslabs may sit above a layer of surface hoar in sheltered terrain and above a widespread hard rain crust (Nov 5 rain crust). This Nov 5 rain crust is found up to 2500m and may become a weak layer where overlaid by windslab. It is buried down 30-100cm depending on wind redistribution and snow depths.
Moist snow during the heat of the day and variable refrozen crusts can be found on solar aspects.
Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches, while the snowpack is much thinner in the valleys and wind scoured locations. The lower snowpack consists of crusts. Weak snow may be developing around these crusts in some areas, which will be a snowpack feature to monitor as the season progresses.
Terrain and Travel
- A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
- Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
- Be careful as you transition into wind affected terrain.
Problems
Loose Wet
The alpine temperature inversion remains a notable concern for loose snow avalanches on steep solar and extreme alpine terrain. This heat will deteriorate the snow more if winds are light and variable. East of the divide temperatures will be warm to valley botom.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Heavy wind redistribution has created varying layers of hard and soft windslabs in the alpine, on lee and cross-loaded features in the alpine, and open "alpine like" features at treeline. These slabs may be poorly bonded to underlying crust and surface hoar layers. Of particular concern is the Nov 05 crust and facet layer which is buried 30-100cm deep in wind loaded areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 5th, 2020 5:00PM
