Avalanche Forecast
Issued: Jan 2nd, 2018 12:45PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Shallow wind slabs may linger in wind exposed terrain above treeline. In some areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steeper slopes.
Summary
Detailed Forecast
After a cloudy start, partly to mostly sunny skies are expected Wednesday afternoon with continued mild temperatures.
Lingering wind slabs should be far less sensitive to triggering on Wednesday and confined to higher terrain. Continue to watch for areas of recently wind transported snow such as fresh cornices, snow drifts, and uneven snow surfaces. Identify and avoid locations where recent wind loading occurred.
Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.
Small loose wet avalanches are possible in isolated areas on steep solar slopes Wednesday, but will not be listed as an avalanche problem. Be aware of the consequence of even a small loose wet avalanche around terrain traps.
In some areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steep slopes.
Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.
Snowpack Discussion
Mild weather seen Sunday through Tuesday has allowed lingering wind slabs to gain strength. A variety of snow surfaces exist including wind scoured snow, crusts, and likely stubborn to unreactive wind slabs.
A variety of rain and freezing rain crusts are sandwiched in the upper snowpack depending on elevation. Current observations do not suggest these layers to be reactive.
Snapshot of selected weather stations at Mt. Hood Meadows and Timeberline over the last 5 days.
Observations
An observation submitted through our public observation page continued to show building wind slabs new Timberline Lodge Sunday. These winds slabs were reported as reactive to ski travel.
On Sunday Mt Hood Meadows Patrol reported a breakable crust below treeline. They observed isolated wind slabs and a very firm crust at higher elevations.
On Saturday Mt Hood Meadows Pro Patrol reported a large natural avalanche in Clark Canyon that likely released during Friday's storm. Debris from this avalanche ran into the near treeline elevation band. While the exact depth of the avalanche is unknown, this was a very large natural avalanche.
Photo: Brian Murphy, Mt Hood Meadows Patrol. Avalanche debris in Clark Canyon from a recent very large natural avalanche. Photo taken on 12-31-17.
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.
Likelihood
Expected Size
Valid until: Jan 3rd, 2018 12:45PM
