Avalanche Forecast
Regions: Mt Hood.
Despite a favorable cooling trend Saturday, wind loading near and above treeline will maintain a Considerable rating with human triggered avalanches likely on lee slopes. A stronger storm with an uncertain track on Sunday should result in rising avalanche danger for the latter half of the weekend.
Detailed Forecast
We just can't shake the Considerable rating near and above treeline in this storm pattern despite a favorable cooling trend late Friday night and Saturday and only light to moderate new loading expected. Lingering wind slab formed earlier in the week shouldn't be much of an issue, but once again persistent S-SW transport winds will build new wind slab on lee slopes late Friday night and Saturday. Watch for firmer wind transported snow and be aware of local loading patterns in your terrain. Shallow storm slabs may build on Saturday in non-wind affected terrain. Â
Cornices should be less sensitive on Saturday, but they are large so continue to give them a wide berth when travelling along ridgelines since they can break further back then expected.Â
The loose wet potential should be minimized by the cooling trend and cloudy skies. If the sun does break out Saturday, mid-March sunshine will rapidly increase the likelihood of loose wet avalanches on steeper solar aspects. Â
A cool yet powerful storm system on Sunday may cause high avalanche danger for the southern Cascades including Mt. Hood by late Sunday afternoon. However, the storm track is uncertain and the avalanche danger will be reassessed with Saturday's forecast issuance.Â
Snowpack Discussion
Weather and Snowpack
The nonstop active weather pattern continues to push a storm system through the PNW almost every day or two resulting in fluctuating snow levels and periods of very strong winds (100+ mph gusts have not been uncommon at the Mt Hood Meadows Cascade Express station over the last 2 weeks).
A last strong storm arrived Wednesday morning bringing heavy snowfall/rain at rising temperatures and very strong S-SW ridgetop winds. About 1.5 inches of water accumulated at the Mt. Hood Meadows and Timberline stations through early Thursday morning, but unfortunately most of the precipitation ended up in liquid form.Â
The mid and lower snow pack at Mt Hood should be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
On Wednesday morning, new extensive wind slabs were forming on lee slopes near and above treeline. Explosive control performed by Mt. Hood Meadows pro-patrol Wednesday produced widespread slab releases on wind loaded N-NE facing terrain with crown depths of 2 feet common. Storm slabs Wednesday morning changed to loose-wet avalanches by midday as temperatures rose and snow changed to rain below treeline.Â
On Thursday, NWAC pro-observer Laura Green toured in the Mitchell and Heather drainages and found evidence of rain up to at least 6600 feet. Thin wind pockets were observed on lee slopes above treeline. A supportable rain crust did not make for good skiing, but on the plus side no avalanche problems were noted. Runnels were observed below 6000'.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: 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