Archived

Avalanche Forecast

Mar 23rd, 2017–Mar 24th, 2017

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

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

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

Regions: Lizard-Flathead.

Wind and snow will build fresh wind slabs throughout the day. Avoid lingering in the runout of avalanche paths because a cornice fall could trigger a large avalanche.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

FRIDAY: Increasing cloud and afternoon flurries with about 5 cm, strong southwest wind, freezing level around 1600 m with alpine temperature around -3 C.SATURDAY: Overnight snow with another 10 cm easing and clearing throughout the day, strong southwest wind, alpine temperature around -5 C.SUNDAY: Mostly sunny, moderate southwest wind, alpine temperature around -5 C.

Avalanche Summary

On Thursday, a few small storm slabs were reported to run naturally overnight in steep alpine terrain and then also react to explosives in the morning (size 1-1.5). More evidence of large deep persistent slab avalanches from last weekend's avalanche cycle were also reported from the Barnes Lake and Cold Feet areas.Expect wind slabs to develop throughout the day on Friday as another pulse of snow and wind arrives in the afternoon. However, the primary concern is the potential for deep persistent slab avalanches triggered by natural triggers such as a cornice fall. See the forecaster blog for advice on managing a low probability - high consequence problem (here) and the accompanying photos (here).

Snowpack Summary

Light precipitation has delivered 15-25 cm of heavy snow at higher elevations, while rain soaked has the snow below about 1800 m. The new snow has fallen on a thick rain crust that has capped the snowpack at all elevations. Daytime warming and sunlight tend to break down the crust in some areas, but it remains frozen on northerly alpine terrain. Isolated basal facets exist in shallow snowpack areas and still have the potential to produce destructive full-depth avalanches.

Avalanche Problems

Deep Persistent Slabs

Heavy triggers such as a cornice fall or wind loading are potential triggers for large avalanches on deep weak layers. Stay aware of overhead hazard when traveling at lower elevations.

Recognize and avoid avalanche runout zones.Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Minimize overhead exposure during periods of heavy loading from new snow and wind.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4

Wind Slabs

Strong winds will be forming fresh wind slabs throughout the day in the lee of exposed terrain.

Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with elevation and aspect.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2