Avalanche Forecast
Issued: Apr 10th, 2018 11:11AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Light snow and moderate winds will create heightened avalanche danger on wind loaded slopes near and above treeline Wednesday. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. Below treeline you may still trigger Loose Wet avalanches or they may be triggered by additional rainfall. Avoid terrain traps if you suspect you could trigger a Loose Wet avalanche.
Summary
Detailed Forecast
Light snow and moderate winds will create heightened avalanche danger on wind loaded slopes near and above treeline Wednesday. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche.
Below treeline you may still trigger Loose Wet avalanches or they may be triggered by additional rainfall. Watch for signs of wet snow conditions such as sluffing, roller-balling and any natural Loose Wet avalanches as signs of an increasing hazard. Avoid terrain traps if you suspect you could trigger a Loose Wet avalanche.
Snowpack Discussion
A front brought rain and wind to Mt. Hood Tuesday. Snow levels fell to around 5500 ft by Tuesday afternoon. Warm and dry conditions were seen on Monday.
The dry weather followed the strong weekend storm that caused rain Saturday to high elevations followed by cooling and new storm snow totaling 1.5-2 ft in the Mt Hood area above 5000 feet through Sunday afternoon. Wet snow avalanches were seen earlier in the storm and continued at lower elevations through the weekend. New Wind and Storm Slabs developed at higher elevations later in the weekend with fresh cornices developing along ridgelines.
Moist or wet snow in the upper snowpack should begin to refreeze near and above treeline Wednesday as colder air arrives.
There are currently no significant layers of concern in the mid or lower snowpack.
Observations
During morning mitigation work Monday, Mt. Hood Meadow Pro-patrol reported that the new snow was not very sensitive to ski triggering. Explosives produced generally shallow soft slabs, with a few that were up to 1-2 ft deep on lee slopes near treeline.
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: Alpine, Treeline.
Likelihood
Expected Size
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.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Apr 11th, 2018 11:11AM
