Avalanche Forecast
Issued: Apr 21st, 2018 11:19AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
While generally safe avalanche conditions are expected Sunday, you can still trigger a small loose wet avalanche on steep sunny slopes or at lower elevations as the day warms. Look for signs of wet surface snow developing as you travel. Avoid slopes with terrain traps where even a small loose wet avalanche could have unintended consequences. Do not linger below slopes overhung by large cornices or where a cornice fall may trigger larger deeper avalanches.
Summary
Detailed Forecast
Sunday should be a fair spring weather day with some building cumulus in the afternoon. Freezing levels should push to near or above 7000 feet after a cool start.
While generally safe avalanche conditions are expected Sunday, you can still trigger a small loose wet avalanche, especially on steep sunny slopes and at lower elevations as the day warms. Look for signs of wet surface snow developing as you travel. New rollerballs, fresh fan shaped avalanche debris, and wet surface snow deeper than your ankle all indicate the potential for loose wet avalanches has developed on similar steep slopes. Avoid slopes with terrain traps where even a small loose wet avalanche could have unintended consequences.
Wind slabs that formed on many slopes near and above treeline last week should be unreactive.
Cornices over the winter have grown very large. Do not linger below slopes overhung by large cornices or where a cornice fall may trigger larger deeper avalanches.
Snowpack Discussion
About an inch of new snow fell Saturday morning as a frontal system largely missed Mt. Hood and affected areas further north. Moderate west winds near and above treeline did not have any new snow to transport. No new avalanches were reported Saturday.
Warm and generally sunny weather affected the snow in the Mt Hood area Thursday and Friday. On slopes receiving sunshine and on lower elevation slopes, moist surface snow conditions developed. The mild weather allowed wind slabs formed earlier in the week time to gain strength.
Significant snowfall accumulated in the Mt Hood area earlier in the week. Around 16-20 inches (40-50 cm) of snow fell Sunday (4/15) through Tuesday (4/17). Strong west-southwest winds during the storm transported the new snow forming wind slabs on many slopes at higher elevations.
While numerous layers can be found within the snowpack, there are no significant layers of concern at this time.
Observations
On Thurday, NWAC professional observer Laura Green traveled in the Mt Hood backcountry. Laura found wind slabs on NE-E aspects near treeline. These wind slabs were still reactive in some snowpack tests. On south-facing slopes, she observed large rollerballs up to 3 ft (90cm) in diameter.
Problems
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: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 22nd, 2018 11:19AM
