Avalanche Forecast
Issued: Feb 2nd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs and Storm Slabs.
ahanna,
Avalanche Canada
While those north of Pemberton continue to tiptoe through mountains plagued by touchy deep persistent avalanche problems, avalanche danger in the south of the region will be MODERATE at all elevations.
Summary
Confidence
Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
Sunday night: Flurries bringing trace to 5 cm new snow. Moderate northwest wind. Freezing level valley bottom.
Monday: Sunny. Light to moderate northwest wind. Alpine high -9 C. Freezing level valley bottom.
Tuesday: Increasing cloud with flurries starting. Southwest wind building to strong, becoming extreme at ridgetop. Alpine high -8 C. Freezing level valley bottom.
Wednesday: Flurries bringing 5-10 cm new snow. Strong west wind, extreme at ridgetop. Alpine high -4 C. Freezing level rising to 700 m.
Avalanche Summary
Numerous size 3-4 deep persistent slab avalanches were reported Saturday in north parts of the region including the Lillooet River valley north of Pemberton and near Goldbridge. Start zones included all aspects 1900-2300 m and avalanches ran to valley bottom, taking out mature timber and blocking waterways.Â
Explosive work conducted Saturday also produced deep persistent size 2-3 in these areas as well as in the Duffey. In some cases, these large touchy slabs were triggered not by detonation, but as the explosive product landed on the slope.
A widespread size 2-3 natural storm slab cycle was observed in most areas toward the tail end of the storm Saturday.
Snowpack Summary
Above 1800 m, weekend storm totals for the north of the region are in the range of 30-50 cm, while the Coquihalla received around 100 cm and the Manning Park area received around 35 cm. Extreme southwest wind during the storm has scoured windward aspects, formed deep loaded pockets in alpine lees and contributed to rapid cornice growth. Below 1800 m, snow overlies a crust and tapers with elevation.
In the north part of the region (ie. Goldbridge/Whitecap/Duffey/Hurley), a few deep instabilities exist in the snowpack, including a weak basal facet crust complex. This has been the failure plane in ongoing reports of very large, deep persistent avalanches.
The south of the region, including the Coquihalla and Manning areas, currently have no concerns about deep instabilities.
Terrain and Travel
- Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.
- Make conservative terrain choices and avoid overhead hazard.
- Be alert to conditions that change with elevation.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Problems
Deep Persistent Slabs
Deep weaknesses near the bottom of the snowpack have been failing under recently applied snow loads, resulting in very large, destructive avalanches. Many of these avalanches have run to valley bottom; hence posing a hazard to all elevations. These layers do not pose an avalanche problem in the south half of the region.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Size 2-3 storm slab avalanches have been observed since the storm. Storm slabs will remain especially sensitive where the wind has deposited recent snow into deeply loaded pockets in lee features.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 3rd, 2020 5:00PM
