Avalanche Forecast
Issued: Mar 3rd, 2018 1:08PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
It is still possible to trigger large and destructive avalanches in wind-loaded, steep, open slopes at upper elevations. Stay off of open, obvious wind loaded terrain steeper than 35 degrees and allow recent wind layers time to heal.
Summary
Detailed Forecast
It is still possible to trigger large and dangerous wind slab avalanches near and above treeline especially 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.
If the sun makes an appearance for extended period of time Sunday, you may see small loose avalanches release on steep slopes.
Snowpack Discussion
A few inches of snow fell during the day Thursday, following on the heels of about 8-10 inches of snow that was deposited Wednesday night through Thursday morning. Strong, mostly SSW winds accompanied Wednesday night's snowfall. This new snow fell on a variety of snow surfaces including crusts on sunny aspects, wind affected 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 Saturday, Mt. Hood Meadows ski patrol reported no new avalanche activity other than small loose wet avalanches on steep solar aspects below treeline.
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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 4th, 2018 1:08PM
