Avalanche Forecast
Regions: Mt Hood.
Moderate to strong W-SW winds will transport new snow onto lee slopes near and above treeline Saturday. New snow is generally expected to bond well to moist snow surfaces and various crusts, but wind-driven snow will likely build unstable wind slab on lee aspects above treeline. The avalanche danger will increase rapidly Saturday night as snowfall increases along with a slow warming trend.
Detailed Forecast
Light snowfall accumulations are expected Friday night through Saturday above 4000Â feet on Mt. Hood.
Moderate to strong W-SW winds will transport new snow onto lee slopes near and above treeline. New snow is generally expected to bond well to moist snow surfaces and various crusts, but wind-driven snow will likely build unstable wind slab on lee aspects above treeline.
Wet loose avalanches may still be locally a concern on steeper slopes at lower elevations so continue to watch for loose wet avalanche potential above terrain traps such as above cliffs, near gullies or where avalanche debris would deeply accumulate.Â
Avoid cornices along ridges and slopes below cornices since cornices may still be weaker due to the warm weather.
The avalanche danger will increase rapidly Saturday night as snowfall increases along with a slow warming trend. This unstable combination of moderate to heavy precipitation and warming should continue on Sunday leading to high avalanche danger in many areas.
Snowpack Discussion
Weather and Snowpack
A large upper ridge and warm air mass aloft over the West Coast from this past Sunday through Wednesday led to the warmest weather of the winter. During this stretch temperatures were generally well above freezing. Â A warm front brought periods of rain to Mt. Hood Thursday night through mid-day Friday, with snow levels falling to 5500 ft after the frontal passage Friday afternoon.Â
The warm temperatures and solar effects earlier in the week caused loose wet avalanches and overall snowpack consolidation while recent rainfall has kept the upper snowpack moist in many areas.Â
Recent Observations
Limited loose wet snow conditions were seen by Tuesday at Mt Hood by the pro-patrol. Moderate winds limited surface snow melt near and above treeline. More significant wet snow conditions were seen below treeline Tuesday through Friday.
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1