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Archived

Avalanche Forecast

Mar 6th, 2017–Mar 7th, 2017
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.

Deep storm snow and recent, fresh wind slabs should maintain dangerous avalanche conditions, especially near and above treeline. Avoid steep slopes recently loaded with wind transported snow. Conservative decision-making remains essential.

Detailed Forecast

Light to moderate snow showers at cool temperatures are expected overnight and Monday. Winds should be moderate and strong enough to easily transport loose surface snow, building some fresh wind slabs on lee exposed slopes.

Generally light accumulations of new snow are expected and with cold temperatures and light to moderate winds this should maintain the current level of avalanche danger. Cold temperatures may help maintain older wind slab layers near and above treeline.

Dangerous avalanche conditions should persist near and above treeline Monday. Cautious terrain selection and conservative decision-making remain essential. 

Cornices won't be listed as an avalanche problem in this area, but avoid travel on ridges, where recent cornices may have formed and avoid steep slopes below cornices, that may fail at any time.

Snowpack Discussion

Weather and Snowpack

The Valentine's day crust is now buried 2-3 feet or more in the Hurricane Ridge area. A weak interface exists several inches above the crust.

Recent storm snow since Friday, ranges from about 12-18 inches in the Hurricane Ridge area. Warming and strong winds during the storm Friday, March 3rd created reactive wind and storm slabs.

Recent Observations

NWAC observer, Matt Schonwald was at Hurricane on Friday and found that ski tests were showing rapidly increasing propagation and increasing sensitivity of the deepening storm slab. Previous winds had loaded various slope aspects while south winds on Friday were loading N aspects.

Reports by NPS rangers early Sunday and a report listed on the NWAC observations page, indicate there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday, March 4th. Including the areas known as Maggies, Hurricane Hill and Sunrise Face. These touchy slab releases indicate the recent storm snow remains sensitive to human trigger and more conservative decision-making remains essential until the storm and wind slabs settle further. 

Avalanche Problems

Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

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: Likely

Expected Size: 1 - 1