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Archived

Avalanche Forecast

Jan 14th, 2015–Jan 15th, 2015
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
1: Low
The avalanche danger rating below treeline will be low
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: Cascades - West.

New shallow storm and wind slab mainly on lee aspects may bond poorly to the existing snow surface Thursday afternoon in the near and above treeline elevation bands. 

Detailed Forecast

On Thursday, an approaching weather system should bring light rain and snow at moderate snow levels during the daylight hours. Mixed precipitation may be seen in the Passes Thursday afternoon. Precipitation will become more intense Thursday evening.

This should minimally increase the avalanche danger Thursday. Shallow new storm and wind slab may develop by the end of the day near and above treeline. Loose wet avalanches seem unlikely below treeline even with rain given the consolidated state of the snowpack.  

On backcountry travel safety note, watch for terrain hazards (exposed rocks, trees, streams, etc.) at lower elevations and on wind scoured aspects. On non-solar aspects with a slick and supportable crust, take extra caution when traversing steep slopes and be prepared to self-arrest if necessary.

 

Snowpack Discussion

West of the crest about 5-15 inches of snowfall on January 4th was followed by about 3 to 7 inches of rain on January 5th with a warming trend. This led to a natural avalanche cycle west of the crest.

Unseasonably high freezing levels with temperature inversions and without any significant precipitation has characterized the weather since the last significant storm.

This drained, further consolidated and generally reset the upper or even entire snowpack. Surface melt-freeze crusts of varying thicknesses formed over stabilized rounded grain layers. Some windward or southerly aspects have little if any snow cover.  Only small wet loose avalanches have been reported recently on southerly aspects. 

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: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1