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Archived

Avalanche Forecast

Feb 1st, 2017–Feb 2nd, 2017
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
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
3: Considerable
The avalanche danger rating in the alpine will be considerable
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.

Strong E-NE winds will form fresh wind slabs Thursday. Wind slabs may be sensitive to triggering where bonding to old snow is weak. Wind slabs should be found near and above treeline, especially on westerly facing terrain, but watch for firmer wind transported snow in all terrain. 

Detailed Forecast

Strong E-NE winds should persist Thursday. The winds will continue to build sensitive wind slabs on a variety of aspects, but mainly near and above treeline. Primary aspects for wind slabs should be any slopes facing west, but may form on a variety of slopes. 

Shallow new wind slab may be particularly touchy in areas where poorly bonded poorly to an underlying crust. Watch for firmer wind transported snow in all elevation bands, especially in open terrain in the upper elevations of the below treeline band. All aspects are listed to cover older wind slab formed over the weekend. Older wind slab should be stubborn to trigger at this point. 

Snowpack Discussion

Weather and Snowpack

An atmospheric river arrived over the Northwest Tuesday 1/17 with heavy rain seen up to at least 6000 feet in the Hurricane Ridge area. A storm cycle from Thursday 1/19 through Sunday, 1/22 deposited about 2 feet of snow at Hurricane Ridge.

A large upper ridge and warm air mass built over the Northwest Thursday through Saturday. Temperatures warmed into the 40s at Hurricane Ridge with south winds in the 20 mph range on Saturday. 

A weak front crossed the PNW Sunday afternoon and night, depositing 1 inch of new snow at Hurricane Ridge through Monday morning after starting as light rain Sunday afternoon. A slight cooling trend under mostly cloudy skies followed on Monday. Tuesday was cool and mostly sunny. Wednesday was cold with increasing easterly winds. The strong easterly winds Wednesday have likely transported any available surface snow building new fresh wind slabs.

Recent Observations

A skier was caught and carried by a wind slab avalanche on the back side of Maggies Saturday. A report with a well done video is available on the NWAC Observations page.

Another report received on Saturday from the Obstruction Point road area via the NWAC Observations page indicated windy and warm conditions, with pinwheels, roller balls and surface crusts on W-SW slopes.

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: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 1