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 11th, 2015–Dec 12th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

Expect deteriorating snow stability as the day progresses and the storm really takes hold. Travel conservatively by staying off steeper slopes and avoiding wind loaded terrain near and above treeline, especially later in the day. The above treeline winds are forecast to be quite strong Saturday afternoon, so don't underestimate the rapid loading occurring at higher elevations.  

Detailed Forecast

Snow will begin by mid-morning and increase in intensity throughout the day. In addition, there should be a gradual warming trend as snow levels peak between around 4000 feet in the late afternoon. Combined with increasing southerly transport winds in the afternoon, there will be an increasing avalanche risk through the daylight hours. 

Storm slabs should become more sensitive and likely to trigger in the afternoon. Wind slabs should also become easier to trigger as they build on NW through E lee slopes throughout the day. The above treeline winds are forecast to be quite strong Saturday afternoon, so don't underestimate the rapid loading occurring at higher elevations.  

Expect deteriorating snow stability as the day progresses and the storm really takes hold. Travel conservatively by staying off steeper slopes and avoiding wind loaded terrain, especially later in the day,

Be aware of early season hazards below treeline. The heavy rains from last week have left many creeks open at lower elevations. 

Moderate to heavy precipitation is expected to continue through Saturday night and much of Sunday, so look for increasing avalanche danger later in the weekend. 

Snowpack Discussion

After the deluge earlier in this week with nearly a foot of rain below 7000 feet, lower snow levels and new snowfall have returned to Mt. Hood. About a foot of new snow has fallen over the 24 hours ending 5 pm Friday, with a few more inches expected through Saturday morning.  

Avalanche and Snowpack Observations

The Mt Hood Pro Patrol on Wednesday reported a generally stable and draining snowpack with wet grains to the ground.  By Thursday new wind slab was developing near and above treeline on lee easterly slopes, but was generally not found to be reactive with ski cuts or in snowpack tests. Ski area control work from Friday showed a few instabilities in the new storm snow, but these were unlikely to propagate. Lighter transport winds Friday should have limited new wind slab development above treeline.   Below treeline should still contain ample terrain anchors, but above 5000' there is enough snow to allow small avalanches in specific areas. No recent observations have been received for the bulk of the above treeline zone due to weather and visibility restrictions. 

Problems

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.