Avalanche Forecast
Regions: Mt Hood.
Surface snow could get a better start on being available for loose wet snow avalanches on Sunday. Continue to avoid cornices and areas below where glide avalanches could be a problem.
Detailed Forecast
The upper ridge and warm air mass should further build over the US west coast on Sunday. This should cause light winds and mostly sunny weather in the Olympics and Cascades with further warming temperatures.
Sun and heat effects should be the main factors to consider on Sunday. From a couple of observations it seems like surface snow was probably pretty solidly refrozen in most areas on Saturday morning. But the refreeze may more limited Sunday morning due to warmer weather. If so then surface snow could get a better start on being available for loose wet snow avalanches.
Loose wet avalanches should remain possible Sunday on steeper slopes involving the recent snow. Watch for wet surface snow getting deeper than your boot tops. Triggered loose wet avalanches should be most likely on steep solar slopes but could be seen on any steep aspect in this warm weather. Avoid areas below steep gullies and run out zones that might be prone to natural loose wet avalanches.
The potential for cornice releases may increase through the warm weekend. Cornice releases are basically unpredictable so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.
Although not listed as an avalanche problem, powerful glide avalanches can release unexpectedly so also avoid areas below steep unsupported slopes or rock faces especially if they are showing glide cracks. Glide cracks may be hidden by the recent snowfall.
Storm and winds slabs will not be listed as avalanche problems along the west slopes due to reports of good bonds of the recent snow to the 4/12 crust and fast stabilizing rates seen at this time of year. However, be aware of the potential for isolated slab avalanche layers involving the recent snow mainly on non-solar aspects of very high terrain.
Â
Â
Snowpack Discussion
Weather and Snowpack
We've had two big warm-ups and spring shed cycles since the end of March. Over this time period the snowpack has undergone significant settlement with lower elevation snow beginning to fade away and with an overall transition to a spring snowpack.
A front crossed the Northwest Tuesday afternoon and night. Then a cool upper and surface low pressure system moved east along the Washington-Oregon border on Wednesday and Thursday. NWAC sites at Mt Hood had 11-14 inches of late season snow in the 3 days ending Friday morning with 6-8 inches of that snow in just the 24 hours ending Friday morning.
Storms in March continued to build unusually large cornices along many ridges. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, should continue for awhile this spring.Â
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
NWAC observer Laura Green was in the Heather, White and Mitchell Canyon areas in low visibility on Thursday 4/14. She found new building wind slab of 20-30 cm by late morning with shooting cracks on N-NE slopes at 6600 feet. Ski cuts were giving easy, small wind slab releases on slopes steeper than 30 degrees.
The Meadows pro-patrol gave the NWAC an extensive report for Friday 4/15. In the above treeline explosive control produced extensive wind slab releases on N-E slopes up to 4 feet deep running on the 4/12 crust. It was felt that these releases could have been triggered by skiers. In the near to above treeline they found ski triggered 4-6 inch wind slab also on N-E slopes but more limited in extent and some small ski triggered and natural loose wet avalanches on E-S slopes.
By Saturday the Meadows pro-patrol reported only some limited small loose wet avalanches in steep terrain. Ski conditions were bad off piste in about 5 inches of wet snow.
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: Possible
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.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 2