Avalanche Forecast

Issued: Mar 10th, 2015 11:00AM

The alpine rating is low, the treeline rating is low, and the below treeline rating is low. Known problems include Storm Slabs.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Shallow storm slabs are possible near and above treeline Wednesday especially on lee easterly aspects. 

Summary

Detailed Forecast

A frontal system should bring light rain and snow to the east slopes Tuesday night and Wednesday. New snow above 5500-6500 ft may form shallow storm slabs near and above treeline, especially on lee easterly aspects, but new slabs should be shallow enough to keep the avalanche danger low. The snowpack should be well drained and setup to handle rain at lower elevations.

Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow (new or existing) to pose an avalanche hazard.

Snowpack Discussion

The last snowfall occurred near the end of February; the central and southeast Cascades received the most snow with 7 inches at Mission Ridge, and generally 2 or 3 inches fell around the northeast Cascades. This was followed by locally strong north to northeast winds that built shallow wind slab on a variety of aspects. Sunny and gradually warmer weather has been seen the first third of March helping to stabilize local wind slab from the end of February and further consolidate the snowpack.

The North Cascade Heli and Mountain Guides in the Washington Pass area over the weekend reported some cool snow on north to east slopes with numerous snowpack tests giving no results. Many slopes above treeline were quite wind and sun-affected, producing variable skiing conditions but no stability concerns. On a positive note, the snow study plot on a north aspect at 6600 ft above Varden Creek measured a snow depth of nearly two and a half meters! Avalanche professionals in the Washington area on Tuesday re-affirmed the overall low avalanche danger. 

Problems

Storm Slabs

An icon showing 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

Unlikely

Expected Size

1 - 1

Valid until: Mar 11th, 2015 11:00AM