Avalanche Forecast
Regions: Mt Hood.
Expect very dangerous avalanche conditions to develop Thursday night and continue through the day Friday on Mt. Hood. Travel in avalanche terrain is not recommended especially near and above treeline Friday.
Detailed Forecast
A first round of moderate snow Thursday night along with shifting winds and a warming trend should be followed by a second round of increasing shower activity and additional warming Friday afternoon translating to a rapidly unstable snowpack in the Mt Hood area Friday.
Expect dangerous avalanche conditions to develop Thursday night and continue through the day Friday on Mt. Hood. Travel in avalanche terrain is not recommended especially near and above treeline Friday.Â
Wind slabs previously formed on westerly aspects will shift back to more traditional easterly aspects as W-SW winds increase Friday near and above treeline.Â
Storm slabs will become increasingly sensitive and may fail due to weaknesses between storm layers or if poorly bonded to previous weak surface snow found in less wind affected areas.Â
Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.
Snowpack Discussion
Weather and Snowpack
An active and cool weather pattern has resulted in a snowy December thus far with Mt. Hood NWAC stations recording about 2-4 feet of lower density snow.
Given the favorable snowpack profile, good bonds between older snow layers and a lack of deeper layer concerns, avalanche problems should be confined to the upcoming old snow/new snow interface or within new storm layering.Â
Moderate easterly winds have shifted to the west along with a warming trend Thursday evening along with rapidly accumulating new snow. There remains ample low density snow available for transport.Â
Recent Observations
On Monday and Tuesday the pro-patrol at Mt Hood Meadows reported only isolated wind slabs in exposed terrain at the upper elevations. These avalanches were fairly shallow within the upper 4-8 inches of snow mostly and released with explosives only. In general, most areas have surface snow conditions lacking slab character with low cohesion snow providing some excellent conditions.
Lastly the indefatigable pro-patrol at Mt Hood Meadows on Wednesday reported light winds that were not causing wind transport. The upper snowpack remains generally right side up with good skiing and riding conditions. Some surface hoar was seen in sheltered locations.
On Thursday shifting winds was producing significant wind transport near and above treeline on Mt. Hood.Â
Avalanche 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: Very Likely
Expected Size: 1 - 1
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: Likely
Expected Size: 1 - 1