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Archived

Avalanche Forecast

Dec 14th, 2018–Dec 15th, 2018
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
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
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Olympics.

Unfortunately much of the recent precipitation has fallen as rain in the Olympics. Cornices and drifted snow are forming at upper elevations and may be unstable. Large variations in snow cover and exposed rocks and vegetation warrant extra caution. 

Discussion

Discussion 

Low snow conditions continue to limit the overall avalanche hazard in the Olympics. A little over a foot of new snow has accumulated in the Hurricane Ridge area since Tuesday, with periods of very strong southerly winds. There is a very wide degree of variation in snow cover based on elevation and especially aspect. On windward southerly facing terrain, much of the area is void of snow cover. While on shaded and wind loaded north to east facing terrain the snow-depths averaged about 4 feet as of Thursday afternoon. Avalanches are possible in wind loaded terrain, especially near and above treeline.  

Forecast schedule

For the 2018-19 winter season, avalanche hazard ratings will be issued for the Olympics Friday through Sunday and during holidays.

On days that the Hurricane Ridge road is closed, No Rating will be applied. We will continue to provide general snowpack and weather summaries for the Hurricane Ridge area even when No Rating is issued. 

Snowpack Discussion

Regional Synopsis 20181214

We made it through our first strong winter storm and are headed into a weekend with dangerous and fickle avalanche conditions. Thick slabs of new snow (2-5 feet) are perched above a weak layer of faceted crystals. Avalanches triggered on this layer could be very large and life-threatening.

Reports continue to come in of very large natural and explosives triggered avalanches in the northern and eastern zones. For perspective, several of these slides have been classified as D3, or large enough to destroy a house.

Anyone accessing alpine areas should limit their exposure to areas where avalanches start, run and stop. In some places, the weak snow will talk to you by whumpfing and cracking. In other places, the heavy blanket of new snow is thick enough that it can give a false sense of stability while it masks the dangerous layering below.

Approximate snow totals from 12/10 - 12/14:  

  • Mt. Baker: 55”

  • Washington Pass: 29”

  • Stevens Pass: 37”

  • Snoqualmie Pass: 28”

  • Paradise: 38”

  • Mt. Hood Meadows: 13”

  • Olympics: mostly rain

The change in the snowpack is pretty dramatic with elevation. Height of snow decreases rapidly below 4500’ at Baker and Washington Pass, 5500’ at Crystal/Rainier. The Passes have better low elevation coverage, but it's still pretty thin below 4000’. With additional warm storms in the forecast, this pattern is expected to continue for a while.

 

Be cautious and get home safe.

Avalanche Problems

Wind Slabs

Highly variable snow-cover exists in this zone. Strong winds have created cornices and 4-5 foot wind drifts on leeward slopes below ridge-lines. Avoid drifted areas where you experience cracking and collapsing in the new snow. 

Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1