Archived

Avalanche Forecast

Feb 19th, 2017–Feb 20th, 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

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

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: Northwest Inland.

Benign weather this week. Watch for isolated wind slabs and shallow snowpack areas where triggering a deep persistent slab avalanche remains possible.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Isolated flurries with trace accumulations, light south winds, alpine temperatures around -8 C.TUESDAY: Cloudy with sunny periods, light northwest winds, alpine temperatures around -10 C.MONDAY: Mix of sun and cloud, light northwest winds, alpine temperatures around -12 C.

Avalanche Summary

On Saturday, numerous small natural wind slabs (size 1-1.5) were reported on northwest aspects around treeline. Small loose dry avalanches running above the rain crust were reported in steep terrain. Watch for isolated pockets where thicker wind slabs could produce larger avalanches. Also keep in mind that a basal weakness continues to drive a low probability/high consequence avalanche problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas.

Snowpack Summary

Clear cold weather and shifting winds have created a variety of surface conditions including isolated wind slabs, pockets of soft snow (5-10 cm deep), sun crusts, and surface hoar. A supportive rain crust exists below 1000 m. A layer of surface hoar that was buried on February 10th may exist 30-60 cm below the surface, but there's a fair bit of uncertainty regarding the reactivity and distribution of this layer. A stiff mid pack sits above weak sugary snow near the ground. Although possibly dormant, this basal weakness has the potential to produce very large destructive avalanches.

Avalanche Problems

Deep Persistent Slabs

A weakness at the bottom of the snowpack is lingering and may be triggered in shallow snowpack areas or by the weight of smaller avalanches.

Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.Avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4

Wind Slabs

Watch for wind slabs on lee and cross-loaded terrain.

Be cautious as you transition into wind affected terrain.Use ridges or ribs to avoid pockets of wind loaded snow.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

Expected Size: 1 - 2