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Archived

Avalanche Forecast

Mar 10th, 2016–Mar 11th, 2016
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
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
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

Wind slabs and cornices along ridges should be less sensitive Friday but still capable of producing large avalanches near and above treeline. The loose wet potential should be relegated to steeper slopes primarily below treeline but will have the potential to entrain heavy wet snow. Avoid terrain traps where even a small yet heavy loose wet avalanche would have serious consequences. You may not see natural avalanche activity Friday, but the human triggered potential remains elevated. 

Detailed Forecast

Clouds should spread over the Olympics Friday as moisture rotates northward and a weak frontal band offshore approaches. Very light precipitation should develop during the afternoon hours. Snow levels should remain moderate Friday, rising along with daytime warming. 

All the travel advice associated with Considerable danger will be pertinent on Friday. Strong winds that loaded slopes Wednesday night and Thursday will require cautious route-finding and conservative terrain selection Friday. Wind slabs and cornices along ridges should be less sensitive Friday but still capable of producing large avalanches in specific areas near and above treeline.

The loose wet potential should be relegated to steeper slopes primarily below treeline Friday but will have the potential to entrain heavy wet snow. Avoid terrain traps where even a small yet heavy loose wet avalanche would have serious consequences. There continues to be a lot of water in our snowpack, so don't underestimate loose wet avalanches in the wrong terrain. 

Snowpack Discussion

Weather and Snowpack

The nonstop active weather pattern continues to push a storm system through the PNW almost every day or two with fluctuating but generally moderate snow levels. The last storm impacted the area Wednesday through Thursday with a warming trend that peaked Wednesday night with the frontal passage in the early morning hours and also featured very strong winds. Winds decreased Thursday afternoon along with decreasing shower activity. Generally 1.5 to 3 inches of water accumulated along the west slopes in the 36 hours ending 4 pm Thursday. Similar amounts were likely seen at Hurricane Ridge. The Waterhole NRCS snowdepth has stayed steady over the last few days due to the alternating periods of rain and snow. 

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

Recent Observations

The ranger at Hurricane reported a foot of new snow on Monday morning with snow sliding off the road cuts and onto the road in many places. The Sunrise path on a northeast slope about a 1/2 mile from the visitor center released an avalanche that entrained snow to about 1' and became 100 feet wide although it could not be determined if it was a loose or slab avalanches due to low visibility.

On Tuesday the ranger added that there had been many 6-12 inch storm slab avalanches on Monday.

No observations were received Wednesday or Thursday, March 9-10th.

Hurricane Weather Station

Internet communications to the station have been disrupted at the NWAC office. We have identified the problem but unfortunately our hardware will not be repaired until early next week. We apologize for the outage and are working to get the station back up ASAP. 

Avalanche Problems

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, West, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1

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, West, 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.

Elevations: Treeline, Below Treeline.

Likelihood: Possible

Expected Size: 1 - 1