Avalanche Forecast
Issued: Jan 21st, 2018 11:31AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Strong southerly winds formed firm wind slabs on lee slopes. Identify and avoid areas where winds have deposited snow along ridges and crossloaded terrain features.
Summary
Detailed Forecast
A break in the weather on Monday will give wind slabs time to heal and gain strength.
Expect highly variable snow surfaces near and above treeline including wind scoured slopes, crust, and firm wind slabs. Firm wind slabs may fail well above a traveler and produce large avalanches. Identify and avoid wind loaded features such as snow drifts, slopes below cornices, and crossloaded slopes.
Snowpack Discussion
An active weather pattern over the last several days deposited 10-14 inches of snow over the most recent 1/17 crust. Observations indicate the recent snow bonded well to the crust.
Winds transported snow significantly in exposed terrain. West winds, seen earlier in the storm period, shifted to the South Sunday. Winds slabs continue to form and grow at all elevations.
Very poor visibility and dangerous travel conditions have made observations in above treeline terrain unobtainable. A high degree of uncertainty exists regarding the extent and sensitivity of wind slabs above treeline.
Below treeline lower snow totals have limited the development of avalanche problems.
Observations
On Sunday, Mt Hood Meadows Patrol reported about 12" of snow over the 1/17 crust. Winds were transporting snow at all elevations.
NWAC Pro Observer Laura Green was in the near treeline area of Heather Canyon on Friday. Recent storm snow had been redistributed by strong winds. Sensitive wind slabs were found on exposed slopes. Mostly shallow storm snow was found well bonded and not reactive to tests below treeline.
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: North, North East, East, West, North West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 22nd, 2018 11:31AM
