Archived

Avalanche Forecast

Dec 29th, 2013–Dec 30th, 2013

Alpine

4: High

The avalanche danger rating in the alpine will be high

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

1: Low

The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

We're expecting moderate snow and very strong upper winds over the next 24 hours. Areas that don't see much snow could see slightly lower avalanche danger on Monday.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Tonight and Monday: Moderate snowfall 5-10 cm. The freezing level is generally around 500 m but an above freezing layer between 1000 and 1500 m is possible. Winds are moderate to strong from the SW. Tuesday: A mix of sun and cloud with a chance of flurries. The freezing level is near valley bottom and winds are light to moderate from the northwest. Wednesday: Another frontal system approaches the coast and could bring periods of snow later in the day. The freezing level is around 500-800 m.

Avalanche Summary

There are a couple reports of recent natural avalanche activity from the Ashman and Hankin areas. In Hankin a couple large slab avalanches (~size 2.5) were observed on northeast facing terrain near ridgetop. These likely released during previous storm and/or wind events and appeared to release near the base of the snowpack. In Ashman a couple smaller storm slabs were observed on steep convex rolls from south facing slopes.

Snowpack Summary

The past few days have brought around 60-70 cm of storm snow with steady strong W-SW winds and fluctuating freezing levels. The most recent storm snow came in with rising temperatures and is likely "upside down" feeling, meaning more dense on top. Expect touchy wind slabs in exposed lee terrain and cross-loaded features well into treeline. A number of rain crusts may exist in the upper and mid snowpack, primarily below 1500 m. Deeper in the snow pack a layer of facets/surface hoar formed in early December may be found in the top 100cm in the Ashman area. The mid and lower snowpack is still structurally weak and faceted. Depth hoar and an early season crust exist near the ground.

Avalanche Problems

Storm Slabs

Another system is set to spread light to moderate snow amounts with strong W-SW winds through Monday. Expect wind slabs to continue building in exposed lee and cross-loaded terrain.

Be cautious as you transition into wind affected terrain.>Choose conservative lines and watch for clues of instability.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 4

Persistent Slabs

Despite the recent snowfall many areas are still below average for snow depths. Deep persistent weaknesses may still exist near the base of the snowpack and could be triggered from thin spots or by continued loading from snow and wind.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid shallow snowpack areas where triggering is more likely.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 5