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Avalanche Forecast

Archived

Jan 14th, 2016–Jan 15th, 2016

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

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.

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.