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Archived

Avalanche Forecast

Apr 5th, 2016–Apr 6th, 2016
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

Significant warming and intense solar radiation Wednesday should increase the likelihood of heat related avalanche problems, especially cornice failures and shallow loose-wet avalanches on steep solar slopes.  Stabilizing shallow wind slab may linger in specific areas at higher elevations, mainly easterly facing. 

Detailed Forecast

Clearing and warming is expected overnight Tuesday through Wednesday.

Any wind slab deposits caused from the shallow snow received Monday, in combination with moderate westerly winds should have mostly stabilized by Wednesday. However, watch for signs of wind slab on mainly easterly facing near and above treeline where extra caution is warranted.  Firm wind transported snow and snowpack cracking can be good signs of wind slab layers. 

Small loose wet avalanches, mainly involving any recent new storm snow from Monday and Monday night will be possible on any steeper solar slopes, especially during the warmest part of the day Wednesday afternoon. 

The likelihood of cornice failure will increase Wednesday from intense solar radiation and warming temperatures. Cornice releases can be unpredictable during the spring so continue to be aware of the overhead hazard and that cornices can break much further back than expected along ridges.

Snowpack Discussion

Weather and Snowpack

A large upper ridge dominated the weather last week through early Sunday, resulting in warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking midweek in the Olympic range. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last week.

A front moved across the Olympics early Monday morning, resulting in a period of mostly light precipitation, cooling and moderate westerly crest level winds.

A mostly cloudy day Tuesday with gradual warming has allowed for a generally decreasing danger as the shallow recent storm snow settles. 

The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC observer, Matt Schonwald toured extensively in the Hurricane Ridge area Saturday, 4/2 and found a well settled and seasonally deep snowpack with very few avalanche concerns. 

During the warm stretch, 1 large glide avalanche (R3-D3) naturally released on the 20th of June slide path (easterly aspect, near treeline) to the ground. According to NPS rangers, the avalanche likely released on Wednesday or Thursday.  

Only shallow amounts of recent snow were received Monday through early Tuesday at Hurricane Ridge. This lead to a slight increase in danger, mainly on specific terrain features such as any exposed lee slopes at higher elevations that received greater wind deposited snow. 

Cloudy conditions and gradual warming by Tuesday afternoon is trending the danger downwards.

Avalanche 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 lips 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.

 

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.

 

A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.

Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1

Loose Wet

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Aspects: East, South East, South, South West, West.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1

Wind Slabs

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, South East, North West.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 1 - 1