Avalanche Forecast
Issued: Mar 5th, 2018 11:59AM
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
It is still possible to trigger large and destructive avalanches in wind-loaded, steep, open slopes at upper elevations. Stay off of open, obvious wind loaded terrain steeper than 35 degrees and allow recent wind layers time to heal. Small loose wet avalanches will be found at all elevations on steeper terrain exposed to direct sunshine. Avoid steep, sun-affected slopes later in the morning.
Summary
Detailed Forecast
Tuesday's weather forecast calls for mostly sunny skies with the potential for cumulus clouds to develop in the afternoon with rising freezing levels.
It may be possible to still trigger a large and dangerous older wind slab avalanches above treeline especially on leeward northwest through north through southeast slopes where drifted wind features exist. These avalanches could be large and destructive if triggered, but these older wind slabs should be trending toward unreactive. Watch for small, fresher wind slabs on mostly easterly aspects near and above treeline. Avoid these avalanches by staying off of snow drifts, deeply pillowed features, and fresh cornices on leeward slopes 35 degrees and steeper.
Expect natural and human-triggered small loose wet avalanches are likely to release within the recent 3" of surface snow on steep slopes on the south half of the compass as the sun impacts the surface snow to higher elevations. Watch for moist snow conditions and roller balls as a sign that these avalanches may for and avoid steep sunny slopes, particularly where a small avalanche may push you into a terrain trap, rocks trees.
Snowpack Discussion
Mt. Hood received 3" of new snow by Monday morning and west winds were transporting snow onto lee slopes (mostly easterly aspects) forming shallow wind slabs about 8" deep that were not particularly reactive. The sun also came out on Monday, warming snow on sun-exposed aspects and creating small loose wet avalanches below treeline.
A few inches of snow fell during the day Thursday, followed on the heels of about 8-10 inches of snow that was deposited Wednesday night through Thursday morning. Strong, mostly SSW winds accompanied Wednesday night's snowfall. A variety of snow conditions exist within the upper snowpack, ranging from sandwiches of soft snow with several crusts on shaded aspects with a multitude of crusts existing on sun-exposed aspects. Wind affected snow and unconsolidated surface snow can be found in shaded sheltered areas.
In many locations more than 3’ of snow now sits on a firm buried crust layer (2/17). This crust has been reported up to 6600’ by professionals in the region. There are currently no significant layers of concern below the 2/17 crust.
Observations
On Monday, Mt. Hood Meadows Pro Patrol reported west winds transporting snow, 20 cm of new and generally non-reactive wind slab on lee aspects limited to E facing slopes. Winds eased mid-day. Small loose wet avalanches occurred on solar, especially below treeline.
On Sunday, an avalanche professional reported no avalanches and no cracking or whumphing observed in the Salmon River Canyon. A test pit at 6200' on a NE aspect indicated right-side up, low-density snow in the upper 12" of snow, with a very thin rimed crust in the upper snowpack and a 1-2 cm more significant crust down 1.5'. A compression test indicated moderate reactivity on this layer.
On Saturday, Mt. Hood Meadows ski patrol reported no new avalanche activity other than small loose wet avalanches on steep solar aspects below 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.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 6th, 2018 11:59AM
