Avalanche Forecast
Issued: Apr 2nd, 2018 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
Be patient Tuesday and allow recently formed wind and storm slab avalanches time to gain strength. Use visual clues such as snow drifts, fresh cornices, and uneven snow surfaces to identify and avoid steep wind loaded slopes near ridgeline and on cross-loaded features. You are most likely to trigger lingering storm slabs near convex rollovers, on unsupported slopes, or in terrain greater than 40 degrees. Conditions can change quickly when the sun comes out. Be ready to adjust where and how you travel as snow surface conditions change Tuesday.
Summary
Detailed Forecast
Avalanche hazard will decrease slightly Tuesday as a break in the weather allows recently formed wind and storm slabs time to gain strength.
You will still be able to trigger wind slabs on lee aspects near ridgelines and mid-slope cross-loaded features. You can use visual clues such as uneven snow surfaces, snow drifts, and cornices to identify and avoid steep wind loaded slopes. Firm wind slabs are difficult to predict and may break well above you. If you suspect a steep slope is wind loaded, stay off of it and allow it time to gain strength.
Storm slabs will slowly gain strength Tuesday becoming harder to trigger. You are most likely to trigger a storm slab near convex rollovers, on unsupported slopes, or in very steep terrain. Avoid these types of features until storm slabs have time to heal.
Expect new rollerballs, pinwheels, and small loose wet avalanches to occur during periods of prolonged sunshine. The April sun is very strong and snow conditions can change quickly. Be cautious on steep slopes where the consequences of even a small loose wet avalanche can be high.
Snowpack Discussion
In general 12-14” (30-35cm) of new snow fell in the Mt Hood area Sunday and Monday. Strong westerly winds during the storm redistributed snow at higher elevations likely forming wind slabs on lee slopes. The new snow fell on a firm melt-freeze crust in many locations forming an initially poor bond.
There are currently no significant layers of concern in the mid or lower snowpack.
Observations
On Monday, Mt Hood Meadows ski patrol reported 1-2 ft (30-60cm) Wind Slab avalanches on lee slopes above treeline during control work. Near treeline, 6-12 inch (15-30cm) Wind Slabs were triggered on wind loaded slopes. Below treeline the 12-14 inches (30-35cm) of recent storm snow lacked slab properties, however Dry Loose avalanches were possible.
On Saturday, Mt. Hood Meadows pro-patrol reported high overcast skies limiting the softening of surface snow on all aspects. No new avalanches were observed.
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
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Apr 3rd, 2018 11:00AM
