Avalanche Forecast
Issued: Jan 25th, 2018 10:30PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
Dangerous avalanche conditions will persist on Friday due to additional snowfall and continuing moderate winds creating the potential for large and destructive avalanches on wind loaded slopes near and above treeline. Avoid steep open slopes connected to large avalanche paths until we exit this storm cycle. Give safe margins near and below growing cornices. Tree-well and snow immersion hazards are very dangerous, so keep communication with your partner at all times.
Summary
Detailed Forecast
Dangerous avalanche conditions will persist on Friday due to additional snowfall and continuing moderate winds creating the potential for large and destructive avalanches on wind loaded slopes near and above treeline. Avoid travel on or below slopes connected to large avalanche paths until we exit this storm cycle.
Due to lower density surface snow available for transport and moderate W-SW winds forecast, wind slabs may develop below treeline or further downslope than you might expect Friday. Avoid travel on slopes if you encounter wind stiffened surface snow, especially on steeper exposed terrain and steep roll-overs. Cold temperatures will preserve new and recent storm instabilities, keeping storm slabs likely in less wind affected terrain. Give safe margins near and below growing cornices.
There's plenty of good snow out there, so maintain a conservative approach to terrain selection.
Significantly transformed snow conditions have taken place during this extended storm cycle. Tree-well and snow immersion hazards are very dangerous, so keep communication with your partner at all times.
Snowpack Discussion
An extended storm cycle continues. Over the past 7 days, 3-4 ft of storm snow has fallen over a strong rain crust buried 1/18. Cool and generally light to moderate showers were seen on Thursday with moderate S-W winds transporting snow near and above treeline.
Warming early Wednesday, along with heavy snowfall and strong winds led to increasingly sensitive avalanches, mainly in terrain exposed to wind affected snow. Slab avalanches of 1-2 ft were common.
Dense storm slabs built quickly early Wednesday, forming over weaker storm snow.
Poor visibility and frequent storm conditions have limited observations above treeline recently, where a high degree of uncertainty exists regarding the extent and sensitivity of wind slabs above treeline.
Observations
On Thursday, pockets of sensitive and firm wind slab were noted near and above treeline in the Mt. Hood Meadows area.
On Wednesday, a professional ski patroller was caught, carried and partially buried in an avalanche he triggered while on duty in a closed area of the Mt. Hood Meadows ski area (SS-AS-R2-D2-O). The avalanche released in an area known as God's Wall, running approximately 600 ft on the old/new snow interface. The bed surface was the firm 1/18 crust. Resources were dispatched immediately and the victim extricated after some difficulty due to low snow and open creeks. He was transported via ambulance to advanced care and is now discharged to recover from his injuries.
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
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 26th, 2018 10:30PM
