Avalanche Forecast
Regions: Mt Hood.
Watch for new or previous firmer wind transported snow on a variety of aspects Tuesday: Don't let the combination of Moderate avalanche danger with non-traditional lee aspects/cross-loaded slopes catch you by surprise!
Detailed Forecast
West winds and snow showers following the front should taper off on Monday with lower snow levels. The avalanche danger should gradually decrease on Monday.
The winds and snow Sunday and Sunday night may have built new shallow wind slabs on lee slopes mainly near and above treeline by the end of the day. Older wind slab may linger on similar slopes. Watch for new or previous firmer wind transported snow mainly on the lee N to SE slopes near ridges or mid-slope where cross loading may have occurred.
New shallow storm slab is possible if you are in an area where more than several inches of snow rapidly accumulated Sunday to Monday morning.
Snowpack Discussion
Weather and Snowpack
Last week, heavy rain and mild temperatures dominated along the west slopes including 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 at times stormy, cooler pattern began to bury the crust on February 17th and brought about 2 feet of storm snow to Mt Hood from Wednesday through Saturday morning. A weak front on Sunday only brought a few inches of additional snowfall through Monday morning.
Storm layers in the snow received from Wednesday to Saturday should be strengthening. Bonding of storm snow to the February 17th crust varied along the west slopes and Mt. Hood initially, but should have also improved over the last few days. Â
The mid and lower snow pack along the west slopes and Mt Hood should be a stable mix of crusts and layers of moist or wet rounded snow crystals.
Recent Observations
NWAC pro-observer Laura Green was in the Newton and Clark Canyon areas on Thursday increasing windy and snowy weather. She reported building wind and storm slab of 8-10 cm with easy hand shears on the February 17th crust.
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.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: Likely
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: South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1