Avalanche Forecast
Regions: Mt Hood.
A greater avalanche danger is expected at Mt Hood on Friday than in the Washington Cascades. Careful snowpack evaluation, cautious route finding and conservative decision making should be essential at Mt Hood on Friday.
Detailed Forecast
A system will move mainly across Oregon and north California on Thursday night. This system should spread some moderate snow as far north as Mt Hood on Thursday night and Friday morning. about 7-10 inches of new snow seems possible at Mt Hood by Friday morning.
New wind slab should be likely on ridges and north to southeast slopes near and above treeline. Watch for signs of hollow snow and firmer wind transported snow.
New storm slab should also be likely on more varied aspects. Fairly steady temperatures are expected which could limit the extent of new wind slab but it would be more extensive if there is any warming.
A greater avalanche danger is expected at Mt Hood on Friday than in the Washington Cascades. Careful snowpack evaluation, cautious route finding and conservative decision making should be essential at Mt Hood on Friday.
Snowpack Discussion
The latest period of snowfall has been from about January 12-14th with about 11-16 inches at Mt Hood. A cooling trend was seen at the tail end yesterday.
Warming Tuesday and early Wednesday caused rain or mixed rain and snow to near tree line by early Wednesday before cooling dropped the snow levels by late Wednesday. Strong winds formed extensive hard slab conditions on lee slopes above treeline. The Mt Hood Meadows pro patrol reported that howitzer control Wednesday produced hard slab avalanches on lee slopes well above treeline though human triggering was unlikely. Near and below treeline, more shallow and isolated pockets of wind slab produced smaller slides with explosives, mostly 8 inches.
By Thursday morning the Mt Hood Meadows pro patrol generally reported about 10 inches of storm snow on a crust from last weekend. Easy clean shears where still reported in the lower part of the storm snow.
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: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: 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