Archived

Avalanche Forecast

Feb 16th, 2017–Feb 17th, 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

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

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.

Cooling temperatures will eventually help stabilize the snowpack, but I'd give the snow a bit more time to settle before pushing into bigger terrain.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

FRIDAY: Cloudy with isolated flurries to the west, light west winds, freezing level dropping to 500 m, alpine temperatures around -10 C.SATURDAY: Mix of sun and cloud, light east winds, alpine temperatures around -12 C.SUNDAY: Mix of sun and cloud, light southeast winds, alpine temperatures around -12 C.

Avalanche Summary

We've received very little in the way of recent avalanche observations, mostly due to inclement weather. At lower elevations where precipitation fell as rain, loose wet avalanches to size 1.5 have been reported. For Friday, expect newly formed wind slabs to be reactive to human triggering. Also keep in mind that a basal weakness continues to drive a low probability/high consequence deep persistent avalanche problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas and during times of warming.

Snowpack Summary

The region received another 5-10 cm of new snow on Thursday. Strong winds likely shifted these accumulations into deeper deposits at higher elevation lee terrain. Below about 1000 m, rain has saturated and settled the snowpack. About 30-60 cm below the surface, you may find surface hoar which was buried on February 10th. There is a fair bit of uncertainty regarding the reactivity and distribution of this surface hoar layer throughout the region. I'd continue to test for this layer before committing to any steeper terrain. A generally stiff mid pack sits above weak sugary snow near the ground. This basal weakness woke up during the last storm and produced numerous large avalanches which released on the ground. The layer has recently been considered dormant but should be monitored, especially during periods of warmer temperatures. It may also be possible for a smaller avalanche to 'step down' to this layer.

Avalanche Problems

Wind Slabs

Watch for fresh and reactive wind slabs in exposed high elevation terrain. Wind slabs may "step down" to deeper more destructive layers including surface hoar buried on February 10th.

Use ridges or ribs to avoid pockets of wind loaded snow.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

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. The potential for a deep release on this layer will remain elevated while warm temperatures persist.

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 4