Avalanche Forecast

Archived

Mar 7th, 2016–Mar 8th, 2016

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

You will need to watch for new layers in some areas and for a combination of winter and spring conditions if you venture out on Tuesday.

Detailed Forecast

A weakening front should move over a flat ridge and over the Northwest Tuesday afternoon and night. Snow from this front should mainly reach the Olympics, the southwest Cascades and at Mt Hood by the end of the daylight hours on Tuesday.

New snow may be enough to form new wind and storm slab layers mainly in the above tree line zones in the Olympics, the southwest Cascades and at Mt Hood by the end of the daylight hours on Tuesday. A rule of thumb is that storm slab is likely when snowfall accumulates at more than an inch an hour for several hours.

Older or previous wind slab may also still be present near and above treeline along the west slopes. Watch for firmer wind transported snow.

Loose wet avalanche conditions may still be possible mainly on solar slopes below tree line along the west slopes. Watch for wet snow deeper than a few inches, pinwheels and natural loose wet avalanches.

Snowpack Discussion

Weather and Snowpack

Last week was wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds (100+ mph gusts were not uncommon at the Cascade Express station).

The latter half of last week and the weekend featured more rain than snow at NWAC sites on Mt. Hood. For perspective, the averaged freezing level measured in March thus far has been 6600 feet at Salem; more akin to spring than late winter.

The mid and lower snow pack along the west slopes should be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The aftermath of the extreme wind event last Tuesday was seen on Wednesday, with any exposed terrain stripped of recent snow, exposing a strong crust. The wind deposits were inconsistent and did not yield much in the way of avalanches, despite a healthy dose of bombs in the Mt Hood Meadows area.

On Saturday the Mt. Hood Meadows pro-patrol reported wet snow up to about 6600 feet with a thin crust above and a well consolidated snowpack in their area. Following the cool down Saturday night, pockets of shallow new wind slab were seen above treeline in the Mt. Hood Meadows area by early Sunday morning.

On Monday there was about 5 inches of new snow and the Mt Hood Meadows pro-patrol reported a variety of conditions including isolated hard 12-18 inch wind slab on ENE slopes above treeline, wide spread sensitive 4-8 inch storm slab near treeline and small ski triggered loose wet avalanches below treeline on solar slopes.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.