Avalanche Forecast
Issued: Mar 2nd, 2018 12:12PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
You will be able to trigger avalanches in wind-loaded, steep, open slopes at upper elevations. Stay off of open, obvious wind features loaded terrain steeper than 35 degrees. Late-winter sunshine on steep sun exposed slopes may trigger shallow Loose avalanches.
Summary
Detailed Forecast
You are most likely to trigger Wind Slab avalanches near and above treeline on leeward northwest through north through southeast slopes where drifted wind features exist. These avalanches could be large and destructive. Avoid these avalanches by staying off of recent snow drifts, deeply pillowed features, and fresh cornices on leeward slopes 35 degrees and steeper.
In wind sheltered locations you can find two feet of recent snow on the ground. With fresh snow and sunny skies, you may see some small loose avalanches release on steep slopes, today. It will be difficult to trigger other storm instabilities in the upper snowpack in sheltered terrain, as the layers are gradually healing.
Snowpack Discussion
About 8-10 inches of new snow was deposited by Thursday morning. Strong, mostly SSW winds accompanied Wednesday night's snowfall. This new snow fell on a variety of snow surfaces created during the last several days including crust on sunny aspects, wind featured snow, and unconsolidated surface snow in shaded sheltered areas.
In many locations more than 3’ of snow now sits on a firm buried crust layer (2/17). This crust has been reported up to 6600’ by professionals in the region. There are currently no significant layers of concern below the 2/17 crust.
Observations
On Friday, NWAC observer Laura Green reported reported ski cuts and test results in sheltered terrain did not indicate the potential for triggering slab avalanches. She did report cracking and propagation on recently wind loaded slopes.
On Thursday, Mt. Hood Meadows pro-patrol reported small to large slab releases reactive to ski cuts near and below treeline on steep slopes. Explosives above treeline released large to very large hard slab avalanches on many N-E facing terrain. These large slabs had crown faces ranging from 4-6 ft deep and produced significant avalanche debris in the runout zones well below the start zones!
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: All elevations.
Likelihood
Expected Size
Valid until: Mar 3rd, 2018 12:12PM
