Avalanche Forecast
Issued: Feb 28th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
cmortenson,
Avalanche Canada
New snow and wind will incrementally load the buried surface hoar and increase slab properties, making the persistent weak layer more easily triggered. Wind slabs are also of concern in exposed and wind-affected terrain. Asses for slabs and make conservative terrain choices.
Summary
Confidence
Weather Forecast
FRIDAY Night: Cloudy with snowfall, accumulation of 5 to 10 cm. Winds moderate southwest gusting strong. Alpine temperature around -12 C with freezing level dropping to valley bottom as cold front passes.
SATURDAY: Cloudy with sunny periods and isolated flurries. Trace precipitation up to 5cm. Winds light to moderate West / Northwest. Alpine high temperature -10 C with freezing level 900 m.
SUNDAY:Mostly cloudy with isolated flurries, trace accumulation. Winds light to moderate west. Alpine high temperature -11 C and lows near -15 C with freezing levels at valley bottom.
MONDAY: Cloudy with snow flurries, accumulation 5 -10 cm. Alpine high temperatures -10 and lows of -14 C. Freezing Level 800m.
Avalanche Summary
A few small to large (size 1 to 2) wind slabs and a few storm slabs were triggered naturally and by humans on Wednesday and Thursday. On Thursday numerous small and a couple large avalanches on the surface hoar layer were reactive to skier traffic on steep and unsupported or convex features. On Wednesday they generally occurred on northerly aspects between 2000 and 2300 m and were 20 to 50 cm thick.
Wind slabs were most reactive in the Northeast portion of the region and were from recent wind loading while persistent slabs released in the south of the region on the surface hoar layer described in the snowpack summary.
Snowpack Summary
Friday night's 5-10cm of new snow will fall with moderate to strong winds and a cooling trend. This will bring total snowfall overlying the widespread layer of surface hoar that was reported to be between 5 and 15 mm in size to 20-45cm.
Recent warm temperatures have built slab like properties in this snow, particularly at mid and low elevations, making the persistent layer more reactive as evidenced in the avalanche discussion. There is variability in the reactivity and distribution of this layer, particularly in the northern half of the region. In the southern half, this layer exists on all aspects and elevations except for steep, sun-exposed aspects where it was melted by sun and formed a melt-freeze crust. So far, the overlying snow has been reactive to human activity where the wind has redistributed it, forming a slab. This has been most common around treeline and alpine elevations in the south of the region.
The mid and lower snowpack is generally well-settled and strong.
Terrain and Travel
- Stick to simple terrain or small features with limited consequence.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Problems
Persistent Slabs
Additional new snow continues to load a widespread layer of surface hoar, with about 30 to 50 cm overlying it now. This layer has been most problematic in the south of the region. So far, the layer has been most reactive at treeline and alpine elevations, where the recent snow has been redistributed by the wind and formed a slab above the surface hoar.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Strong southwest wind has formed wind slabs in exposed terrain. Use added caution in lee terrain features, particularly near ridges.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 29th, 2020 5:00PM
