Avalanche Forecast
Regions: Mt Hood.
A pattern change will begin to take place over the Northwest on Friday. You will need to pay lots of attention to conditions and forecasts during the transition Friday and Saturday if you decide to venture into the back country.
Detailed Forecast
A pattern change will begin to take place over the Northwest on Friday. Dry weather and strong cold E-NE winds seen Wednesday and Thursday will get replaced by increasing southwest flow aloft, increasing rain or snow and milder temperatures Friday and Saturday. You will need to pay lots of attention to conditions and forecasts during the transition Friday and Saturday if you decide to venture into the back country.
Wind slab formed by strong E-NE winds on Wednesday and Thursday will linger on Friday. The primary aspects for these wind slabs should be any W facing slopes but could be found on other aspects.
New sensitive wind slab is likely to begin forming as shower bands of snow begin to move across the Cascades on Friday with a slight warming trend. The primary aspects for these wind slabs should be NW to SE facing slopes except for W facing slopes in the Cascade Passes.
Wind slab may be more touchy in areas where poorly bonded poorly to an underlying crust or firm old layer. Watch for firmer wind transported snow in all elevation bands especially in open terrain in the upper elevations of the below treeline band. All aspects are listed for wind slabs to account for the strength of recent winds and for any lingering older wind slabs formed over the weekend. Â
New storm slab is also likely to begin forming on Friday on more sheltered slopes in areas that see more than a few inches of rapidly accumulating snow. The warming trend will help build upside down layers and promote storm slab formation.
Snowpack Discussion
Weather and Snowpack
An atmospheric river arrived Tuesday 1/17 with rain up to about 7000 feet on Mt. Hood. From Thursday 1/19 through Sunday 1/22, generally 15-20 inches of snow accumulated at NWAC Mt Hood stations.
A large upper ridge and warm air mass built over the Northwest last Thursday to Saturday 1/26-1/28. By Saturday temperatures had reached the 40's.
A front crossed the Northwest Sunday afternoon causing moderate southwest winds, slight cooling and no measurable precipitation through Monday morning. Westerly winds above treeline were strong Monday night through Tuesday morning with occasional periods of light snow.Â
Strong NE-E winds have been seen Wednesday and Thursday with very cold temperatures. Fresh, touchy wind slabs formed with large plumes of snow visibly transporting loose snow from exposed terrain.
Recent Observations
No recent observations.
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: All aspects.
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: Likely
Expected Size: 1 - 1