Avalanche Forecast
Regions: Mt Hood.
A drastic change from the recent weather is underway. Very wet and mild weather should substantially increase the avalanche danger through Wednesday. Natural wet snow avalanches are likely and travel in avalanche terrain is not recommended.
Detailed Forecast
An avalanche warning is in effect through Wednesday afternoon: Expect periods of heavy rain and strong winds to continue Tuesday night through Wednesday afternoon. The wet and milder weather should substantially increase the avalanche danger through Wednesday.
The heavy precipitation with a warming trend through Tuesday night and Wednesday will impact the Mt Hood area. A natural avalanche cycle should occur with the heaviest precipitation.
An abundance of weak and cold snow in the upper snowpack especially near and below treeline 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.Â
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
Warm, wet and windy weather has returned to the Cascades as Tuesday with the rain intensities really increasing Tuesday afternoon, 1/17 to all elevation bands.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
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1