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
Watch out for increasing reactivity on the buried surface hoar. Once a threshold amount of snow forms slab properties, slab avalanches will become more easily triggered and larger at all elevations and aspects. Choose terrain to limit your exposure & assess every slope.
Summary
Confidence
Weather Forecast
FRIDAY NIGHT: Snow with accumulations of 5-15 cm with more amounts in the Monashee Mountains and near the highest mountains of the region. Winds moderate southwest gusting Strong. Alpine low temperatures -10 C with freezing level dropping to 800 m.
SATURDAY: Cloudy with scattered flurries, accumulation Trace to 10 cm. Winds light to moderate west. Alpine high temperatures -9 with freezing levels to 1000m.
SUNDAY: Morning flurries then a mix of sun and cloud. Winds light west. Alpine temperature -12 C with freezing levels near 800m
MONDAY: Cloudy with flurries, accumulation 5-15cm. Winds light southwest gusting strong. Alpine high temperatures -5, lows to -9 and freezing levels rising to 1400m
Avalanche Summary
Many small (size 1 to 1.5) persistent slab avalanches were triggered by humans every day since Tuesday. They occurred at all elevation bands, between 1600 m and 2300 m, and generally on northwest to east aspects. Early reports from Friday suggest an increase in the number of large avalanches, including a few remotely triggered avalanches on North and East aspects in the Alpine and at treeline. Avalanches were commonly 20 to 40 cm deep and released on the surface hoar layer described in the Snow pack Summary. There were also reports of large natural avalanches on Solar slopes or in steep terrain.
There is uncertainty as to how this persistent weak layer will respond to the continued loading of snow, but we expect avalanches to increase in size as the slab properties of the overlying snow pack increase.
Snowpack Summary
Friday night's forecast 5-15cm of new snow will result in a total of 35-50cm overlying the widespread layer of surface hoar that was reported to be between 5 and 20 mm in size. This surface hoar layer is showing variability in its reactivity and distribution, but has been reported at all elevations and aspects. Recent warm temperatures have built slab like properties in this snow, particularly at mid and low elevations, making the persistent layer more reactive as evidence in the avalanche discussion. As surface snow continues to gain slab properties with more snow, wind, and Friday's warming trend, activity on this layer is expected to increase and avalanches may grow in size.
The mid and lower snowpack is generally well-settled and strong.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Persistent Slabs
35 to 50 cm of snow overlies a widespread layer of surface hoar found at all elevations and on all aspects. Recent warm temperatures have settled this snow into a more cohesive slab in mid and low elevations, making it more likely to produce large avalanches. To date, the layer has been most reactive between around 1700 and 2300 m and where the overlying snow has gained slab properties from snow load, settlement and wind affect. This elevation band of reactivity may increase in the coming days as new snow and strong wind continue to increase slab properties.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Friday night's snow and recent South west and Westerly winds will also contribute windslab formation in the Alpine and at exposed Treeline locations. Buried and fresh windslabs and wind effect have been reported in Alpine and on exposed features at treeline. Use added caution in lee terrain features, particularly near ridges.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 29th, 2020 5:00PM
