Archived

Avalanche Forecast

Mar 24th, 2017–Mar 25th, 2017

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

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

Regions: Lizard-Flathead.

Wind and snow will build fresh wind slabs overnight Friday into Saturday. Avoid lingering in the runout of avalanche paths as a cornice fall could trigger a large avalanche.

Confidence

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

Weather Forecast

There is significant uncertainty regarding precipitation amounts for Friday into Saturday. Unsettled weather and isolated flurries Sunday onwards. SATURDAY: 5-20cm possible Friday overnight with strong southwest winds.Light flurries easing off throughout the day on Saturday. Freezing level 1500m , alpine temperature around -4 C.SUNDAY: Sunny with some cloudy breaks, moderate southwest wind, freezing level 1600mMONDAY: Isolated flurries with 2-4 cm possible. Moderate southwest wind, freezing level around 1700 m with alpine temperature around -2 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 into Saturday 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 has soaked the snow below about 1800 m. The new snow is bonding well to 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

Wind Slabs

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

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

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4