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Avalanche Forecast

Archived

Mar 5th, 2016–Mar 6th, 2016

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

Regions

Mt Hood.

Wet snow conditions will prevail below treeline with a transition to shallow storm hazards above treeline. Avoid steeper slopes where even a small loose wet avalanche could entrain significant amounts of recent snow or where you could be flushed into a terrain trap. Be wary of unstable layers created during heavier showers that would make shallow wind or storm slabs found at higher elevations more likely to trigger.

Detailed Forecast

Light to moderate rain Saturday night will transition to showers Sunday morning with a slow cooling trend during the day. Showers may occasionally be intense on Sunday forming unstable storm layers.   

The avalanche danger will temporarily rise Saturday night during periods of peak rainfall. On Sunday, wet snow conditions will prevail below treeline with a transition to shallow storm hazards above treeline. Avoid steeper slopes where even a small loose wet avalanche could entrain significant amounts of recent snow or where you could be flushed into a terrain trap. Be wary of unstable layers created during heavier showers that would make shallow wind or storm slabs found at higher elevations more likely to trigger.

Cornices formed over the last week should still be weakened by the mild temperatures so be aware of the overhead hazard. 

Non-avalanche hazard: Despite our seasonally, healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.  

Snowpack Discussion

Weather and Snowpack

The last week has been relatively mild and occasionally wet with a series of active fronts transiting the region and causing fluctuating freezing levels and periods of very strong winds (100+ mph gusts were not uncommon at the Cascade Express station).

The latter half of the week including Saturday has featured more rain than snow at NWAC sites on Mt. Hood. For perspective, the averaged freezing level measured in March thus far has been 6700 ft at Salem; more akin to spring than late winter.  

Thursday and Friday saw mild temperatures and sunshine or filtered sunshine. This allowed for melt-freeze conditions on solar aspects with some nice softening during the day. 

The recent highly variable weather this week has left a variety of snow surface conditions, with firm exposed crusts the most frequently encountered. Wind slabs should be isolated to specific terrain features, as well as cornices. 

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 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. 

Observations Thursday, March 4th confirmed the mainly stable exposed crusts with variable wind transport to isolated features.

On Saturday, Mt. Hood Meadows pro-patrol reported wet snow up to about 6600' with a thin crust above and a well consolidated snowpack in their area. 

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.

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.

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.