Avalanche Forecast
Regions: Mt Hood.
Watch for locally sensitive wind slabs on lee slopes near and above treeline and sun affects on steeper solar slopes Tuesday afternoon.
Detailed Forecast
Tuesday should be partly to mostly sunny with a gradual warming trend. Recent shallow storm snow should continue to settle, but sunshine and increasing temperatures in the afternoon may activate loose wet avalanches predominately on steeper southerly slopes. Especially watch above treeline, where more snow is available for entrainment and could funnel you into a terrain trap. Â
Also, there may be pockets of sensitive wind slab mainly on N-SE aspects near and above treeline. Â
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Snowpack Discussion
Strong southwest flow carried a warm and wet front across the PNW Saturday night. This front tapped subtropical moisture pushed snow levels pretty high on Mt. Hood resulting in 3.5 - 4.5 inches of rain at NWAC sites. A cooling trend Sunday along with another inch of water ended as 4-5 inches of new snow between 5-6000 feet by Monday morning.Â
NWAC observer CJ Svela was at Timberline on Sunday. He found consolidated P and 1F layers in the top meter of the snowpack but no avalanche activity in this area. Mt. Hood pro-patrol reported wind transport Mon AM leading to a thin and soft wind slab above treeline. West winds eased off more quickly than forecast Monday and new wind transport was not likely significant.Â
The mid and lower snowpack at Mt Hood should also mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm stretches so far this winter.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.
Elevations: Alpine, Treeline.
Likelihood: Possible
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: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1