Avalanche Forecast

Issued: Mar 19th, 2023 4:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Deep Persistent Slabs and Persistent Slabs.

Avalanche Canada TH, Avalanche Canada


Following a week full of avalanche activity and incremental warming through the weekend with strong solar inputs, cloudy skies and cooling will limit the potential for natural avalanche activity into the start of the week.

Human triggering of the lingering persistent and deep persistent layers remains a concern.




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

10-20 cm of snow buries a layer of surface hoar, facets and sun crust (March 12). Suncrusts are forming on steep solar slopes in the alpine and are more widespread below.

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

A trough will bring cloudy skies, cooler temperatures and some light snow accumulations through Tuesday.

Monday, freezing levels around 1800m winds will be light.

Tuesday, freezing level will stay near valley bottom.

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.


Deep Persistent Slabs

An icon showing 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.



Expected Size

2 - 4

Persistent Slabs

An icon showing 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.


Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Mar 20th, 2023 4:00PM