Avalanche Forecast
Issued: Jan 14th, 2015 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
NWAC,
Northwest Avalanche Center
New shallow storm and wind slab mainly on lee aspects may bond poorly to the existing snow surface Thursday afternoon in the above treeline elevation band.
Summary
Detailed Forecast
On Thursday, an approaching weather system should bring light snow during the daylight hours. 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 above treeline.
East of the crest in the Central Zone the likelihood of triggering a persistent slab is considered very low.
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
East of the crest about 6-12 inches of snowfall on January 4th was followed by about 1-3 inches of rain on January 5th with a warming trend. This led to a natural avalanche cycle east of the crest. In the northeast Cascades at higher elevations more of the precipitation fell as snow before precipitation ended than elsewhere.
Unseasonably high freezing levels with strong temperature inversions and without any significant precipitation has characterized the weather since the last significant storm. No avalanches have been reported recently east of the crest.
The Mission Ridge pro-patrol last Friday reported that the wet and warm weather had stabilized the upper snowpack and formed a supportable crust in most areas. Depth hoar involved in large skier triggered avalanches in this area around the New Year remained intact but unreactive to explosives on previously uncontrolled slopes. Pro-observer Tom C. near Jove Peak on Wednesday found a faceted layer 85 cm down on a southerly aspect generally unreactive in snowpit tests.
While it is highly unlikely for a human to trigger a persistent slab down to this layer we will continue to call this avalanche problem out in the central east zone.
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.
Likelihood
Expected Size
Valid until: Jan 15th, 2015 10:00AM
