Avalanche Forecast
Regions: Mt Hood.
Above treeline, dangerous avalanche conditions should develop through the day with storm or wind slabs becoming touchy by afternoon. At lower elevations, shallow wet snow conditions should maintain the possibility of mostly small loose-wet avalanches. Avoid overhead hazard, such as the recently formed large cornices.
Detailed Forecast
A weak disturbance will spread increasing light rain and snow at gradually rising freezing levels overnight Monday. Only light amounts of precipitation are expected overnight. This should begin to wet and weaken shallow surface snow layers.
A stronger band of moisture Tuesday should bring periods of moderate rain and snow at gradually rising freezing levels. Winds should be moderate along the ridges above treeline Tuesday.
These conditions should cause dangerous avalanche conditions through the day, building fresh wind slabs at higher terrain along ridges, mainly on NW-NE-E facing terrain. The wind slab problem should become increasingly sensitive to human trigger, especially by Tuesday afternoon. Watch for firmer wind transported snow on all aspects, especially in areas of complex terrain.Â
At lower elevations, light rain should maintain shallow wet snow conditions and make small loose-wet snow avalanches possible.
Avoid areas with terrain traps where a small loose wet avalanche could have unintended consequences.Â
It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC stations at Mt Hood piled up about 6-7 ft of snow.
The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately, these systems delivered far more rain than snow. At least two regional avalanche cycles occurred during the stretch. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures.Â
After a short respite from the active weather pattern on Thursday, another strong low pressure system brought about an inch of predominately rain to the NWAC Mt. Hood stations Friday night and Saturday morning. Rapid cooling late Saturday morning was followed by snow showers with light new snow accumulation. Strong W-SW winds were transporting new snow above treeline by mid-day Saturday.Â
Sunday was cool with light winds and mostly sunny skies at Mt. Hood. Â Increasing clouds Monday with moderate daytime warming allowed additional slow snowpack settlement.Â
Recent Observations
Mt. Hood Meadows pro-patrol reported a switch from rain to snow at mid-mountain by noon Saturday with strong W-SW winds beginning to build fresh new wind slab above treeline.Â
NWAC Observer, Laura Green was out Saturday and observed a snowscape of deep rain runnels from overnight rains. Along exposed ridges in higher elevations, wind slabs were forming along lee ridges as well as cornices. Â
Avalanche Problems
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, West, North West.
Elevations: Alpine.
Likelihood: Likely
Expected Size: 1 - 1
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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1