Avalanche Forecast

Archived

Jan 18th, 2016–Jan 19th, 2016

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

Mt Hood.

Dangerous wind slabs may be large to very large on Tuesday. While some of these may be difficult to human trigger, it may be possible to release large avalanches if triggered from a shallow area of the slab. Dangerous avalanche conditions exist, making conservative decision-making and cautious route-finding is essential.

Detailed Forecast

A weak front should pass overnight Monday, followed by light showers tapering off Tuesday morning. Another frontal system is expected late Tuesday afternoon and night.

New, shallow wind slab should be found mainly on lee north to east slopes near and especially above treeline. Generally avoid wind loaded slopes above treeline.

Wind slab should be found mainly on lee north to east slopes near and especially above treeline. Very large avalanches are possible on lee slopes if initial releases are able to step down to a crust formed earlier this month. Generally avoid wind loaded slopes above treeline.

Snowpack Discussion

The latest period of active weather from January 12-18th has accumulated about 3 feet of snow at both the Mt. Hood Meadows and Timberline Mt Hood NWAC stations. Fluctuating snow levels over this period has occasionally mixed rain up into the near treeline elevation band during this storm cycle.

A very active day on avalanche control was seen at Mt Hood Meadows Friday. The pro patrol reported explosively triggered widespread 1-4 foot slab avalanches on north to east slopes above treeline releasing on a crust from last weekend along with very sensitive ski cutting as well.

On Saturday, rain moved up to at least 6000 feet by late morning with snow levels lowering by mid-afternoon. Visibility was limited, but Meadows pro-patrol found 8-12" wet slabs very sensitive to ski cuts on steeper slopes below treeline. Steady winds continued to load lee aspects near and above treeline Saturday. Another 0.50 - 1 inch of water on Sunday brought up to 6 inches of wet snow at Meadows and Timberline through 5 PM.

The most recent 6-9 inches of snow received by early Monday fell at steady temperatures, but with strong winds above treeline, likely building new wind slab and hard slab conditions on lee slopes above treeline.

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.