Avalanche Forecast
Issued: Jan 20th, 2020 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Stable snow conditions exist after yesterday’s warm temperatures. New snow and wind arriving Tuesday will begin to develop new avalanche problems later in the day. Look for changing conditions throughout the day and stay clear of steep, lee slopes rapidly accumulating more snow than the surrounding slopes.
Summary
Discussion
Warm weather and clearing allowed for the snowpack to continue settling and stabilizing. An active cycle of loose wet avalanches also helped stabilize conditions near and below treeline. A slight crust now covers the generally stable snowpack. Upper elevation slopes also experienced some warming, but cold, dry snow still exists under the surface and weak layers in the recent storm snow may still exist.
Clearing on Sunday offered the first look at the upper mountain after an active 10 days of weather. A very large avalanche was observed on the Newton Headwall. It likely occurred during the storm last week, but highlights continued uncertainty about the snowpack at upper elevations.
A very large crown around 10,000’ on the Newton Headwall of Mt Hood which likely occurred during the storm last week. Photo: Kevin Kayl
Debris from the Newton Headwall avalanche in Newton Canyon. Debris filled the valley floor and extends to 5000’! Photo: Nick Burks
Snowpack Discussion
New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.
Problems
Wind Slabs
New snow and wind will begin to develop wind slabs on lee slopes at upper elevations by Tuesday afternoon. A melt-freeze crust exists on most aspects. Expect generally stable conditions during the day, but as snow accumulates, investigate the bond between new snow and the crust below using small test slopes. Look for blowing snow, fresh cornice development and cracks in the snow as signs that you could trigger an avalanche on similar slopes. Avoid slopes steeper than 35 degrees on which wind transported snow is accumulating more rapidly than nearby slopes.
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 21st, 2020 10:00AM
