Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 4th, 2015–Dec 5th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

.

This is a potentially dangerous setup heading into the weekend! Persistent slabs may be human triggered where persistent weak layers were buried intact. Stay on low angled slopes and watch and listen for obvious clues like shooting cracks and whumpfing. Use caution until more information is obtained about PWLs throughout the east slopes. 

Detailed Forecast

A frontal system should take aim mainly at the northeast Cascades Saturday, with light precipitation beginning for the northeast Cascades mid-morning. Cold air bottled up on the eastside of the Cascades will mitigate a slow warming trend found along the west slopes. 

Recent observations have identified a reactive persistent weak layer in the Stevens Pass area but we don't have any specific information about PWLs in Washington Pass or Icicle Creek/Enchantments area.  

This is a potentially dangerous setup heading into the weekend! Persistent slabs may be human triggered where persistent weak layers were buried intact. 

Stay on low angled slopes and watch and listen for obvious clues like shooting cracks and whumpfing and use caution until more information is obtained about PWLs spatial variability and likelihood to trigger throughout the east slopes. 

New wind slabs and storm slabs, generally shallow, are possible on all aspects by later in the day Saturday.  

Early season hazards exist for much of the below tree-line band throughout the Northwest, so ski and ride with caution. 

Snowpack Discussion

Note: The snowpack discussion is for the entire east slopes of the Cascades, but the avalanche danger forecast varies by zone.  

 

The northcentral and northeast Cascade zones have been privy to the deepest snowdepths found throughout the Cascades this season thanks to cold air pooling on the east side in otherwise warm storms for the west slopes. Snowdepths are generally between 1 to 2 meters near the crest. Long stretches of cold weather under high pressure has lead to near surface faceting and surface hoar formation around the end of November.  At the end of November, professionals in the Washington Pass area reported faceting near the surface crust, and overall a general variety of snow surfaces.  

Roughly 15-20 inches of new snow fell at the NWAC Washington Pass, Holden Village Co-op site and Lyman Lake Snotel stations over the last few days. Unlike in the Stevens Pass area, this new load may have adequately tested PWLs on the east-side of the Cascades and led to a natural avalanche cycle. 

Further away from the crest for areas like Mission Ridge and for the southeast Cascades, less avalanche problems are likely as well as less snow. Mission Ridge pro-patrol reported no control work and no PWLs in their area near and above treeline due to warmer and windy recent weather.  

We still have many gaps in our observation network as it's early season, so make your own observations and use them in co-junction to our regional avalanche forecast. Thanks for reading the first NWAC avalanche forecast for 2015-16 season, stay safe and have fun! 

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.