Avalanche Forecast
Regions: Mt Hood.
Dangerous avalanche conditions are expected on Sunday with large storm or wind slab avalanches expected in some areas. Careful snow pack evaluation and cautious route finding will be necessary on Sunday.
Detailed Forecast
The next strong cool cold front will cross the Northwest Saturday night and Sunday morning. This will renew moderate to heavy snow in the Olympics and Cascades Saturday night and Sunday morning with a minor warming trend but the snow level will stay below the passes. It looks like the heaviest snow will shift to Oregon Sunday.
Rapid loading will cause new storm and wind slab will build Saturday night and Sunday. It looks like the most snowfall will be on the volcanoes including Mt Hood where 1-2 feet should be seen by later Sunday so the avalanche danger should be greatest on the volcanoes. This means that some large natural or triggered storm and wind slab should be seen in some areas during the main part of the storm Sunday morning at Mt Hood. But these conditions could easily last all day Sunday.
Terrain anchors are still causing significant anchoring at the lowest elevations. Use caution near creeks which are still open in some areas.
Snowpack Discussion
Another rain event Thursday on Mt Hood caused rain to about 7000 feet. This has been followed by about 1.5 feet of snow the past 2-3 days at Mt Hood with low snow levels.
NWAC pro observer Laura Green visited the Heather and Newton Canyon areas on Thursday and reported rapidly changing conditions with plentiful cracking and natural or easy to trigger heavy storm slab of 20-25 cm.
Widespread storm slab avalanches were also seen Thursday at Mt Hood Meadows with reports from the pro patrol of widespread sensitive and sympathetic storm slab of 8-12 inches.
New storm slab layers have stabilized somewhat by Saturday. The Mt Hood Meadows pro patrol reported no more results from avalanche control on Saturday with much improved stability.
The general break in the weather should bring some further stabilizing on Saturday.
Avalanche Problems
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: Likely
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1