Avalanche Forecast

Issued: Jan 13th, 2018 10:13AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Icy snow surface conditions will have a difficult time breaking down on Sunday, limiting avalanche hazards near and below treeline. Above treeline winds during and post storm has created a variety of snow surface conditions, including firm wind slabs. Monitor changes in surface snow conditions as you travel.

Summary

Detailed Forecast

Another mild and sunny day Sunday is on tap in the Mt Hood area. Light easterly flow will bring slightly cooler temperatures. Wind transportation of snow will be limited to isolated, exposed features where winds can accelerate. Expect shallow new wind slabs and older deep wind slabs on a variety of aspects.

The stout icy surface crust will have a difficult time breaking down, even with warm temperatures and mostly sunny skies. While loose wet avalanche are not expected, monitor changing surface snow conditions. It only takes a few inches of wet surface snow to create loose wet conditions. This is most likely in steep rocky sun exposed terrain where shallow snow and rocks can accelerate the heating process.

Icy surface crust near and below treeline, and a variety of snow surfaces above treeline will continue to make travel difficult in the Mt Hood area.

Snowpack Discussion

A building high pressure ridge brought warm temperatures and mostly sunny skies to the Mt Hood area Saturday. This allowed the first real views into above treeline terrain in several days.

Friday, a rain and freezing rain event created icy surface conditions up to at least 7000 feet. While this surface crust softened on Saturday it did not entirely break down.

Above treeline, W-SW winds Wednesday through Friday combined with significant snowfall have likely created a variety of snow surface conditions, including firm wind slabs in the alpine.

Observations

Observations Friday from Mt Hood Meadows reported a supportable rain and freezing rain crust to 7000 feet. The ice crust prevented winds from transporting snow near and below treeline.

Problems

Wind Slabs

An icon showing 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.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Jan 14th, 2018 10:13AM