Avalanche Forecast
Regions: Mt Hood.
A mixed bag of spring avalanche problems Friday will keep heightened avalanche conditions in specific terrain. You can mitigate the loose wet and cornice risk by being aware of the terrain you are connected with and by recognizing the rapidly increasing hazard in locations that warm quickly. Firm wind transported snow and snowpack cracking that might be found on any aspect can be good signs of wind slab layers.
Detailed Forecast
Sun on Friday morning should give way to some high clouds by Friday afternoon with warmer temperatures. Strong east winds are likely in places along the Cascade crest.
Stronger mid-March sun should make loose wet avalanches possible on steeper solar aspects on Friday after quickly breaking down sun or melt-freeze crusts. Loose wet avalanches may start small but could have the ability to entrain recent moist snow in specific terrain. Watch for rapidly increasing hazard in locations that warm quickly.
Northwest winds on Wednesday likely continued to build wind slab on lee aspects in the upper elevations of the above treeline band. This wind slab will mostly likely be found on N-SE facing slopes.
But east winds Thursday and Friday will also possibly build new wind slab on west aspects in places along the crest.
So recent and new wind slab will be indicated on most aspects in the above and near treeline on Friday. Wind slab may also be locally possible in the below treeline on west slopes in areas that have east winds on Friday. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.
Recently formed cornices have grown large and can become sensitive when it is warm and sunny. Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices in the spring.
Snowpack Discussion
Weather and Snowpack
Storms moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels. Two deep surface low-pressure systems moved across the Olympic Peninsula last week with the first passing last Thursday, March 10th and the next on Sunday, March 13th. These systems caused very stormy weather. Â
Cool and showery weather Monday through Wednesday morning along with prolonged westerly winds deposited additional snow at lower snow levels.Â
Storm totals on Mt Hood have been impressive over the last 4 days with about 4 feet of new snow accumulating through early Wednesday morning at the NWAC Mt. Hood Meadows and Timberline stations! Â
The mid and lower snow pack at Mt Hood should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
The Mt Hood Meadows pro-patrol on Sunday reported stormy conditions with widespread wind and storm slab of 6-12 inches on all aspects in the area, easily triggered by ski cuts and running on the crust buried on Thursday.
A report for Newton Canyon via the NWAC observations page for Monday indicated stormy weather and numerous ski triggered 3-10 inch storm slabs.
On Monday and again Tuesday, control performed by Mt. Hood Meadows pro-patrol produced extensive and sensitive wind and storm slab avalanches triggered by ski cuts in lower elevation slopes and explosives in wind loaded terrain. Avalanches were greatest on N-E facing terrain. Loose wet slides were releasing on solar aspects by Tuesday afternoon below treeline.
On Wednesday, Meadows patrol were still finding hard wind slab of up to a foot above treeline on the usual lee aspects with a rising hazard of loose wet avalanches in steeper terrain below treeline due to warming and sunbreaks.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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
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, South West, West, North West.
Elevations: Alpine, Treeline.
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: Possible
Expected Size: 1 - 1