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Avalanche Forecast

Archived

Feb 24th, 2016–Feb 25th, 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.

Earlier formed wind slabs should continue to stabilize, but remain aware of these potentially touchy wind slabs on a variety of aspects, most likely those facing westerly. Strong late winter sunshine and mild temperatures should cause possible loose wet avalanches on steeper solar slopes in your area. 

Detailed Forecast

The wind slabs that formed Monday night through Tuesday from strong E-SE winds, primarily in the near and above treeline elevation bands, will continue to settle and stabilize, but may still be possible below treeline depending on local loading patterns.  

Mild temperatures Wednesday and again Thursday should allow these layers to quickly stabilize, however watch for stiffer previously wind transported snow on a variety of aspects Thursday.  

Temperatures should be even warmer Thursday, so watch for pinwheeling and rollerballing as precursors to more significant loose wet activity and especially be wary of loose wet avalanches around terrain traps, such as slopes that would funnel wet snow like gulleys or depressions, also slopes above cliff bands or dense trees. 

Snowpack Discussion

Weather and Snowpack

Last week, heavy rain and mild temperatures dominated on Mt. Hood, forming the latest rain crust. NWAC sites at Mt Hood recorded about 2.5 inches of rain over the 2 days ending Tuesday morning February 16th.

An active and cooler pattern began to bury the crust on February 17th and dropped about 2 feet of snow at Mt Hood stations from Wednesday through Saturday morning. A few additional inches of snow fell from Sunday through Monday morning.

Storm layers in the snow received from Wednesday to Saturday have had many days to stabilize. Bonding of storm snow to the February 17th crust varied along the west slopes and Mt. Hood initially, but also should have improved over the last few days.

Moderate E-SE winds Monday night and Tuesday at Mt. Hood likely redistributed recent surface snow and built shallow, but new wind slab in all elevation bands. 

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 Mt Hood Meadows pro-patrol reported large explosively triggered 2-3 foot hard wind slab on north to east slopes in the above tree line Saturday. In the near and below treeline storm snow was well bonded to the February 17th crust with some small, easily triggered storm slab on isolated terrain features.

Several reports from the Mt. Hood pros on Monday indicated a generally stable snowpack with minimal sun affects on solar slopes and some scoured windward slopes above treeline due to the persistent westerly transport winds. Loading patterns were reversed on Tuesday, likely cross-loading some 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.

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.