Avalanche Forecast
Regions: Mt Hood.
There should be enough heavy rain on Thursday and Friday to break down the recent freezing rain crusts and tap into softer snow below the crusts and cause loose wet snow avalanches. Wet slab avalanches seem possible.
Avoid the lower parts of avalanche paths that start higher on the mountain!
Detailed Forecast
The active changeable pattern will continue on Friday. Another moist system arrives on a SW flow. A surface low will track across across NW Washington and a cold front will move across the Cascades Friday evening. What this means at Mt Hood is stormy crest level winds and a lot of rain on Thursday night and Friday.
The outcome of so much rain and the current snowpack at Mt Hood is difficult to predict. There should be enough heavy rain on Thursday and Friday to break down the recent freezing rain crusts and tap into softer snow below the crusts and cause loose wet snow avalanches. Wet slab avalanches seem possible.
Here is a big heads up for Mt Hood: avoid the lower parts of avalanche paths that start higher on the mountain! Large or very large avalanches starting from higher on the mountain and running into the above, near and below treeline areas seem possible or likely.
Snowpack Discussion
A very big change is underway compared to the past 5 days of quiet weather. The Northwest will experience a very active changeable weather pattern Thursday and Friday with moist systems crossing the Pacific Northwest.
On Thursday strong westerly flow aloft is carrying a very moist occluded front across the NW. Winds and snow are ramping up on schedule at Mt Hood on Thursday at sunset.
The frontal zone will remain over the South Cascades and Hood zones Thursday night with the strongest crest level winds and heaviest rain or snow possibly in the south Cascades and Mt Hood.
It has been an "interesting" past week for weather at Mt Hood with some mixed precipitation including yet more freezing rain Wednesday. A weather disturbance also moved across the southern WA Cascades and Mt Hood area Christmas Eve into Christmas Day, depositing 6-10 inches of snow before unfortunately ending with freezing rain and forming a surface crust. Prior to this storm, about 15-18 inches of low density snow fell at Mt Hood in the 24 hours ending Saturday morning 12/23.
Observations
NWAC pro-observer Laura Green on Thursday reported that the freezing rain crust remained stout and predominant on the surface of the snowpack up to about 7300 ft.
On Wednesday morning 12/27, Mt. Hood Meadows Patrol reported a rain/freezing rain crust at 5200 ft thickening with elevation up to 6600 ft. Some wind transport of recent snow was occurring above treeline.Â
On 12/26 the Mt Hood Meadows Patrol reported that wind slabs were more stubborn to trigger during control work. A 1 cm freezing rain crust had formed near the surface.
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1