Avalanche Forecast
Issued: Feb 4th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
JSmith,
Avalanche Canada
Human triggering of LARGE avalanches continues to be LIKELY on Friday. The persistent weak layer of surface hoar will be slow to gain strength and requires continued conservative terrain choices.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations.
Weather Forecast
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THURSDAY NIGHT: Cloudy with isolated flurries; 0-3 cm. / Light, northwest ridgetop wind / alpine low temperature -14 / Freezing level valley bottom.
FRIDAY: Cloudy with isolated flurries; 0-3 cm. / Strong, northwest ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.
SATURDAY: Cloudy with flurries; 0-3 cm. / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.
SUNDAY: Cloudy with isolated flurries; 0-3 cm. / Moderate, northwest ridgetop wind / alpine high temperature -12 / Freezing level valley bottom.
Avalanche Summary
On Tuesday, several skier triggered storm slabs up to size 2 and numerous explosive triggered storm slabs up to size 3 were reported near Golden.Â
Most notable was a report of skier remotely triggering a size 2.5 storm slab from a ridgetop at treeline near Quartz Creek. This avalanche failed on the very weak layer of surface below the recent storm snow. It was reported that light wind effect had stiffened the recent storm snow just enough to be highly reactive to skier triggering. Min report HERE.
Touchy storm slabs are sitting on a weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.
Snowpack Summary
Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.
40-60 cm. of recent snow is sitting on a very weak layer of surface hoar which has potential to surprise backcountry users by how easily it may be triggered and how wide the persistent slabs propagate across slopes. Recent avalanches on this layer have primarily been reported at treeline and below.
60-100 cm. down is an older surface hoar and/or a thin melt crust from mid January. This layer was more prominent in the north Purcells in sheltered, open slopes at treeline.
Deep persistent weak layers can still be found in the lower snowpack. These weak layers are most likely to be triggered from rocky areas with a shallow or thin to thick snowpack.
Terrain and Travel
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- In times of uncertainty conservative terrain choices are our best defense.
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Be careful as you transition into wind affected terrain.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Persistent Slabs
40-60 cm of recent snow has formed reactive slabs sitting on a persistent weak layer of surface hoar. These slabs may be especially reactive in wind affected terrain.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Wind Slabs
Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 5th, 2021 4:00PM
