Archived

Avalanche Forecast

Mar 5th, 2017–Mar 6th, 2017

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

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

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Lizard-Flathead.

A week of heavy snowfall and strong winds have left large storm slabs and cornices primed for human triggering. Avoid overhead hazards and stick to mellow terrain.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

We're looking at scattered flurries and cool temperatures throughout the forecast period. MONDAY: Cloudy with scattered flurries and 5-15 cm of new snow, light gusting strong south winds, alpine temperatures around -7 C. TUESDAY: Isolated flurries with up to 5cm of new snow, 20-40 km/h south winds, alpine temperatures around -8 C. WEDNESDAY: Light flurries with 5-10cm possible, 20-30 km/h south winds, alpine temperatures around -9 C.

Avalanche Summary

Cornices are large and remain easy to trigger. See here for a great MIN post from Sunday illustrating just how surprising the results can be. Several size 1.5 to 3 natural and explosives triggered avalanches were reported on Saturday. Aspects were east through northwest, from 1500m to ridgetop.A widespread natural avalanche cycle occurred on Friday night, with many size 2-3 cornice triggered avalanches on north and east aspects. Natural activity is expected to taper off, but storm slabs will remain primed for human triggering.

Snowpack Summary

Another 20 cm of snow fell on Friday, bringing the three day storm total to roughly 80 cm and the weekly total to over 120 cm. Strong southwest winds have extensively redistributed the snow and formed large brittle cornices. The new snow came in "upside down" (heavier, denser snow over lighter snow) and is rapidly settling into a slab which sits over a variety of old surfaces including surface hoar, facets, stiff wind slabs, sun crusts, and a rain crust below 1900 m. Isolated basal weaknesses may still exist in shallow snowpack areas and appear to isolated to north-northeast aspects in the alpine.

Avalanche Problems

Storm Slabs

Storm slabs are primed for rider triggering, especially on leeward slopes and behind terrain features that are wind loaded.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.The new snow will require several days to settle and stabilize.Avoid leeward slopes as a thicker, reactive slabs will likely exist.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Cornices

Always look up and avoid exposure to overhead cornices.

Stay well back from cornices.Do not travel on slopes that are exposed to cornices overhead.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood: Likely

Expected Size: 1 - 3

Deep Persistent Slabs

There have been two natural deep persistent slab releases in the past week. Both of these avalanches were on northeast aspects in the alpine, and released to size 3 or larger.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for large, deep avalanches.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 4