Archived

Avalanche Forecast

Mar 13th, 2023–Mar 14th, 2023

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Glacier.

A healthy snowfall at the Pass has reset the slopes, but the storm snow will take some time to properly bond to the underlying layers, especially where the snow landed on a crust.

Confidence

Moderate

Avalanche Summary

A natural avalanche cycle is underway (Monday afternoon) in the highway corridor as the snow falls and the temps rise. Numerous slides in the sz 2-3 range have been detected from most aspects.

Natural activity should subside quickly with dropping temps on Tues.

Snowpack Summary

Warm storm snow has fallen on a variety of surfaces (wind crust, sun crust, or surface hoar), accompanied by gusty SW winds. This storm slab is presently widespread through the region.

The generally strong snowpack sits on a deep persistent basal weakness of rounding facets/decomposing crust near the ground. Uncertainty surrounds this layer; each major snowfall has the potential to finally overload this weakness, resulting in large avalanches.

Weather Summary

The main thrust of moisture has passed the region, with unsettled weather Tues and general clearing/cooling Wed/Thurs.

Tonight: Flurries, trace snow, Alp low -14*C, mod/strong SW winds, freezing level (FZL) valley bottom

Tues: mix of cloud/sun, Alp high -10*C, light/mod S winds, 900m FZL

Wed: mix of sun/cloud, isolated flurries, Alp high -10*C, light/mod W winds, 900m FZL

Terrain and Travel Advice

Closely monitor how the new snow is bonding to the crust.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Cornice failures could trigger very large and destructive avalanches.

Avalanche Problems

Storm Slabs

Storm slabs now dominate the upper snowpack, with ~30cm of warm snow sitting on a variety of old surfaces (wind crust, sun crust, surface hoar). Deeper storm slab exists in wind loaded areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Deep Persistent Slabs

Monday's storm brought ~30cm of heavy, warm snow at higher elevations, with a hint of rain below Treeline. This additional load will test the integrity of the deep persistent weak layer. An avalanche on this layer would be very destructive, likely run full path or further, and be of high consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 2.5 - 4.5