Avalanche Forecast
Issued: Jan 20th, 2018 10:59AM
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
Avalanche conditions will worsen throughout the day on Sunday. Winds throughout the storm period have reshaped surface snow creating a variety of snow surfaces including firm wind slabs. Travel with large safety margins Sunday, as wind slabs can be very difficult to assess.
Summary
Detailed Forecast
A frontal system will slowly move into the Mt. Hood area on Sunday with increasing precipitation and winds expected during the daylight hours. Wind and storm slabs developed over the past couple of days will continue to grow and potentially become more reactive. Expect avalanche conditions to worsen throughout the day.
Above treeline a lack of recent information has created a high degree of uncertainty. Expect very difficult travel conditions due to poor visibility and varied snow surface conditions.
Below treeline smaller amounts of new snow continue to limit avalanche danger. Pay attention to exposed features where winds may alter snow surface conditions, creating wind slabs normally found at higher elevations.
Snowpack Discussion
New storm snow continues to accumulate in the Mount Hood area. By Saturday afternoon, 8-12 inches of storm snow has fallen since Wednesday, with more snow expected at higher elevations. The bond between the new snow and 1/17 crust is gaining strength.
Moderate to strong westerly winds throughout the storm period has significantly redistributed recent storm snow. Reports indicate some windward slopes have been stripped down to the old surface crust. On lee slopes wind deposited snow drifts can exceed 2 feet.
Very poor visibility and dangerous travel conditions has made observations in above treeline terrain unobtainable. A high degree of uncertainty exists above treeline.
Observations
On Saturday Mt Hood Meadows Patrol reported 5 inches of snow in the past 24hrs. Near treeline, westerly winds created stubborn wind slabs on lee aspects.
NWAC Pro Observer Laura Green was in the near treeline area of Heather Canyon Friday. Recent storm snow had been highly re-distributed 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, South East, North West.
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 21st, 2018 10:59AM
