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Avalanche Forecast

Archived

Jan 14th, 2015–Jan 15th, 2015

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

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 afternoon hours to Mt. Hood. Precipitation will become more intense Thursday night.

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

At Mt Hood 5-10 inches of snow on January 4th was followed by about 2-3 inches of rain on January 5th with a warming trend. This likely caused natural avalanches.

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.  No avalanches have been reported recently at Mt. Hood. 

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.