Avalanche Forecast
Issued: Jan 24th, 2018 1:17PM
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 Thursday, especially in terrain receiving wind transported snow. Avoid steep open slopes. Give safe margins near and below growing cornices. Storm snow is very deep! Tree-well and snow immersion hazards are very dangerous, so keep communication with your partner at all times. Storm layers will take extra time to stabilize.
Summary
Detailed Forecast
Moderate rain and snow late Wednesday should taper to light to moderate showers with a cooling trend overnight Wednesday and Thursday.
Increasing crest level winds are expected Wednesday night and Thursday.
The avalanche danger will lower slightly Thursday, but it will take time for these deep storm slab layers to stabilize, mainly at lower elevations with little wind exposure. Near and above treeline, strong winds should continue to build wind slabs along lee slopes below ridges and exposed open terrain.
Dangerous avalanche conditions will persist due to the likelihood for triggering a large and potentially deadly avalanche. Recent storm and wind slabs will require time to heal, so be patient and match your terrain selection appropriately, namely very conservative.
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 6 days, 3+ ft of storm snow has fallen over a strong rain crust buried 1/18.
Warming early Wednesday, along with heavy snowfall and strong winds led to increased 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 Wednesday, there was an avalanche accident involving a professional avalanche worker. A wind slab of 2-3 ft was triggered and the individual was caught, carried and partially buried. Rescue was quick and the victim was responsive and transported to hospital for evaluations. Hoping for a good outcome. More information will be forthcoming.
On Tuesday Mt. Hood Meadows Pro Patrol reported rain to 3800'. Wind slabs were building near and above treeline on top of lower-density snow received over the weekend. The slabs were sensitive to skier triggering down to the crusts from 1/16 or within the storm snow. Slab depth was variable. Winds were moderate near and below treeline and strong above treeline.
On Monday morning, Mt Hood Meadows Pro Patrol reported 6" of new snow at 5300' and 13" at the top of their terrain that fell on Sunday night. Wind slabs up to 1' were found into near treeline terrain, with the larger releases triggered by explosives.
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 25th, 2018 1:17PM
