Avalanche Forecast
Issued: Mar 18th, 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
After a week full of avalanche activity: 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
Since the latest storm, we have seen avalanches almost every day failing on the deep persistent layers.
See the other bulletin for the region for Saturday's avalanche control results in Yoho NP.
Friday avalanche control on Mt Whymper produced avalanches with every shot: Small slab results were observed with the March 12 Persistent Layer. Large slabs to sz 3 were observed on the Deep Persistent Layer, several of which initiated directly to the base of the snowpack. Finally, several pockets: slabs to sz 2 in themselves, were sympathetically triggered by other avalanches in motion on SW facing features. These were initiating on the January Persistent Layer of crusts.
Snowpack Summary
15-25 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 40-110 cm.
The weak Nov. 16 basal facet layer is down 50-130 cm producing sudden results in snowpack tests.
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.
Sunday, the winds should be very light. Freezing levels will reach to near 2000m and solar heating may bring temperatures to peak values, however, as the ridge breaks down some convective activity can be expected in the afternoon which may curb heating. Overnight, a trough will bring increasing cloud cover and flurries.
Monday up to 5cm of snow may be possible with freezing levels reaching to about 1600m.
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 this week. Multiple parties have remote triggered large slabs from thin areas in the snow pack. 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
15 to 25cm 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 40-110 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 19th, 2023 4:00PM
