Avalanche Forecast
Regions: Mt Hood.
A drastic change in the recent weather is expected. The timing is uncertain, so watch for changing conditions. Very wet and milder weather should substantially increase the avalanche danger late Tuesday or Tuesday night. Natural wet snow avalanches are increasingly likely later Tuesday.
Detailed Forecast
Light rain and snow should develop for the North Cascades Monday night while only thickening clouds are expected for the Mt Hood area. Mild freezing levels will continue Monday night. Alpine winds out of the SW are forecast to increase Monday night. Â
Light to moderate rain, snow or freezing rain is expected Tuesday with increasing SW winds. This weather will begin an increase in the avalanche danger as shallow wind and storm slabs begin to develop. Warming and rain should cause loose-wet avalanches on many steep slopes.Â
Avalanche watch issued Tuesday night through Wednesday:Â A drastic change in the weather pattern to wetter and milder weather should substantially increase the avalanche danger Tuesday night through Wednesday. Â
Heavy precipitation with a warming trend late Tuesday and Tuesday night should cause a more widespread natural avalanche cycle.
Over the Mt Hood area, precipitation amounts, type and timing are less certain and High avalanche danger may occur late Tuesday or not until Tuesday night. Â
An abundance of weak and cold snow in the upper snowpack combined with the potential for rapid warming and high precipitation rates would lead to very dangerous avalanche conditions during this period and backcountry travel is not recommended later Tuesday.
Snowpack Discussion
Weather and Snowpack
A low pressure system tracked across Oregon Tuesday morning through Wednesday afternoon. Mt. Hood was stacking up the new snow Tuesday with 15-20 inches falling Monday night through Wednesday midday. Winds were generally light to moderate in this storm, but E winds increased mid-mountain Tuesday afternoon, then switched to SW Wednesday.
An upper ridge over the northeast Pacific Ocean has caused fair weather Thursday through Monday over the Mt Hood area with mostly light winds and moderating temperatures.Â
Surface hoar and near surface faceting has been noted widely throughout the Cascade range in sun and wind sheltered locations below treeline. Sun crusts have formed on steeper solar aspects over the last few days.Â
Recent Observations
On Wednesday, Meadows pro-patrol did not venture above about 6600 feet due to white-out conditions. Below this elevation, in the mostly below treeline band, sheltered slopes were maintaining right side up powder conditions that lacked any slab structure, providing excellent conditions.
On Thursday, the pro-patrol reported one natural 8 inch x 300 foot wide natural slab avalanche that occurred Wednesday on a south slope at 6500 ft. Otherwise on Thursday only pockets of 4-10 inch wind slabs were released by explosives on N-NE slopes in the near and above treeline due to SW winds on Wednesday.
A couple reports for Mt Hood area available via the NWAC Observations page for Thursday. A skier on the north side of Mt Hood noted E and W wind effects and potential wind slab in the near and above treeline. Another skier on Pea Gravel Ridge noted limited, thin wind slab near the top of the Ridge but otherwise snow was right side up and cornice and ski tests gave no results.
NWAC pro-observer Laura Green was touring in the east fork of Hood River up to 6100 ft on Friday. She found the upper snowpack generally non-reactive in snowpack tests with good skiing conditions especially below treeline. Good surface hoar growth was noted up to 6100 ft.Â
We did receive one report of an 8-10" soft slab triggered below treeline on an easterly aspect that occurred Saturday. While we believe slab avalanches are unlikely below treeline, small avalanches remain possible in isolated areas.Â
Avalanche 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: Likely
Expected Size: 1 - 1
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: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood: Likely
Expected Size: 1 - 1