Avalanche Forecast
Regions: Mt Hood.
The avalanche danger will push the needle towards the higher end of Moderate danger on Friday as small loose wet avalanches become likely with warming but will be specific to steeper slopes. Larger avalanches caused by glide releases or cornice fall are possible in isolated areas. Get off steep slopes early in the day and be aware of the overhead hazard to minimize your exposure.
Detailed Forecast
Mostly sunny and warm weather is expected again on Friday. The avalanche danger will push the needle towards the higher end of Moderate danger on Friday. Get off steep slopes early in the day and be aware of the overhead hazard to minimize your exposure.Â
Loose wet avalanches will become likely on any steeper slope due to warming Friday. Pay attention to the integrity of surface crusts formed overnight. Backcountry travel early in the day is recommended since conditions can change rapidly due to daytime warming. Watch for wet snow deeper than your boot tops especially on steep solar slopes during the late morning to afternoon hours.
The potential for cornice releases will continue on Friday. Cornice releases can be unpredictable during the spring so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.
Any wind slab deposits caused from the snow received Monday in combination with moderate westerly transport winds should have stabilized by Friday.Â
Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.
Avalanche activity on Friday is not expected to be as extensive as during the warm weather last week which more closely followed a period of heavier snowfall and caused consolidation and some stabilizing. Hence the Moderate avalanche rating in all areas versus the Considerable rating forecast last week. You will need to evaluate avalanche conditions on specific terrain features and change your plans if snow conditions are more dangerous than expected.
Snowpack Discussion
Weather and Snowpack
A large upper ridge dominated the weather last week through early Sunday, resulting in very warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking Thursday or Friday during the warmest temperatures and lightest winds. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last week.
A front moved across the Mt Hood area early Monday morning, resulting in a period of moderate precipitation, cooling and moderate to strong westerly crest level winds. Precipitation transitioned from rain to snow as cooling occurred, forming a generally good bond to the old melt freeze crust. Showers at cooling temperatures occurred overnight Monday and Monday night. Storm snow amounts on Mt Hood ranged from 6-12 inches as of Tuesday.
Another upper ridge is currently over the Northwest causing sunny weather and warm temperatures with most NWAC stations on Mt. Hood pushing into the 60s Thursday afternoon!Â
Frequent March storms have built large cornices along many ridges.
The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
Following the recent snowfall Monday and Monday night, on Tuesday 4/5 the Meadows pro-patrol reported only isolated avalanche results. Moderate to strong winds appeared to have displaced much of the storm snow, rather than building wind slabs in the typical places, hence only isolated results were achieved and those from large explosives. Good bonding of recent snow was also noted with the old moist surface.
Middayon Wednesday 4/6 the Meadows pro-patrol reported no avalanches within the ski area but some triggered loose wet avalanches on the upper mountain. Increasing wet surface snow with boot penetration was seen on Wednesday of about 15 inches to the crust from last week.
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
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2