Avalanche Forecast
Issued: Nov 25th, 2016 10:18AM
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
Human triggered avalanches will become more likely above treeline in areas that experience significant wind loading. Storm slabs should be less sensitive on Saturday but use caution while navigating avalanche terrain and take it slow, the season is just beginning!
Summary
Detailed Forecast
A warm front lifting north Friday night should bring light precipitation to the Cascades, except locally heavier near Mt. Baker through late Saturday morning. Along with the precipitation, there should be a moderate warming trend even in the Cascade Passes through mid-day Saturday.
Warmer temperatures and time will help the most recent snow settle and recent storm slabs should become less reactive to human triggering. Rain below treeline should have a limited effect on the avalanche danger due to the shallow snowpack and abundance of terrain anchors. The avalanche danger will be rated higher in the Mt. Baker area where heavier precipitation is expected. Expect the avalanche danger to be locally lower in the Cascade Passes were there is less snow and more terrain anchors.
Wind slabs found above treeline should be the most sensitive avalanche problem on Saturday. Strong winds above crest level will transport snow to lee aspects, loading mainly NW through SE aspects.
Use caution at lower elevations where creeks, rocks and other early season terrain hazards lurk just below the surface; your body and equipment will thank you!
Snowpack Discussion
Mt. Baker was the hands down winner over the last 48 hours, with almost 4 feet of snow through Friday afternoon! Crystal, Chinook and Paradise also did quite well with 1-2 feet over the same time period. Lower storm totals were seen elsewhere including the Cascade Passes.
Along the west slopes of the Cascades we heard from Crystal mountain pro-patrol today. Morning avalanche control work at Crystal produced widespread 8-10" storm slabs that released within the new storm snow. Storm slabs were the most sensitive in areas with the least wind effect. We also heard from the NPS ranger at Paradise that a skier triggered storm slab caught and carried a skier on a SE aspect of Mazama Bowl Friday afternoon. The shallow slab was about 10 cm (4") deep, 30 m across and ran 25 m vertically, failing within the storm snow. The skier went for a ride but was uninjured. We expect that in the Mt. Baker area where due to the higher storm totals, storms slabs were more reactive and deeper.
Below treeline new snow has begun to cover terrain anchors and fill in creeks, though many areas need more snow to transform the landscape to full winter conditions. This particularly applies to the Cascade Passes where the snowdepth is still quite shallow.
It's early season and the forecasts are based on limited field observations. Keep that fact in the forefront of your mind if entering avalanche terrain this weekend.
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: Nov 26th, 2016 10:18AM
