Avalanche Forecast
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. Â
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. Â
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.Â
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.Â
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. Â
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1