Avalanche Forecast
Issued: Mar 17th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Persistent Slabs and Persistent Slabs.
TH,
Avalanche Canada
Avalanche Control is planned in Yoho National Park for Saturday March 18. No activities on Mt Dennis, Mt Stephen, or Mt Field please. The Field Back Road is closed to all vehicle traffic and pedestrians.
While there has been markedly less avalanche activity this week in this zone of the forecast region: Factor in the effects of rising freezing levels and solar inputs as you select your objectives this weekend.
The avalanche problems described will become more sensitive to human triggering as the snowpack warms up and the potential will increase for snow to move as cornice failures or small solar triggered events which could initiate these slabs as well.
Summary
Confidence
Avalanche Summary
Very little avalanche activity has been observed in this zone for the week however many avalanches on the deep persistent layer have been seen throughout the week in the remainder of the forecast region.
Snowpack Summary
20-30 cm of snow buried a layer of surface hoar, facets and sun crust on March 12. Suncrusts are forming on steep solar slopes.
The midpack comprises various Jan crust layers that are now down 60-120 cm.
The weak Nov. 16 basal facet layer is down 90-190 cm.
Weather Summary
The region will continue to sit under the influence of a high pressure system until late on Sunday. Heating will be the most significant weather influence to the snowpack for the period.
Freezing levels will rise to near 1800m Saturday afternoon. While solar heating may bring alpine temperatures close to 0C, SW winds reaching just into the moderate range are likely to keep heating in check at that level.
Sunday, the winds should back off. Freezing levels will reach to near 2000m and solar heating may bring alpine temperatures as high as 5C.
Terrain and Travel Advice
- Uncertainty is best managed through conservative terrain choices at this time.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Deep Persistent Slabs
The weak depth hoar at the bottom of the snowpack inspires little confidence. We have seen increased activity on this layer through the week in most areas of the forecast region with the exception of the deeper snowpack areas around Little Yoho. Give careful consideration to the slopes overhead as large avalanches may run well into the runout zone or into lower-angle terrain. Avoid big terrain features and be especially cautious in thin or rocky areas, where triggering is more likely.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
20 to 30cm fell during the storm to bury a layer of surface hoar, facets and sun crusts on March12. Isolated pockets of wind slab were also formed near ridge crests. Following the end of the storm we have seen limited amounts of activity on this layer however it has been around long enough, and raises enough concern, to now be classified as a persistent slab.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Three persistent weak layers formed in January are down 60-110 cm. Buried sun crusts on steep solar slopes present the greatest concern for triggering, however, weak facets and isolated surface hoar can be found on the same interfaces on shaded aspects.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 18th, 2023 4:00PM
