Avalanche Forecast

Archived

Dec 14th, 2018–Dec 15th, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Olympics.

Avoid cornices along ridges built by strong winds and snowfall. Watch for wind drifted snow in steeper terrain. Be cautious due to variation in snow cover and exposed rocks and vegetation.

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.

Problems

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.