Avalanche Forecast
Regions: Mt Hood.
Strong winds built new wind slabs near and above treeline. Dangerous avalanche conditions exist, especially on steep lee slopes near or above treeline. Evaluate the snow and terrain carefully and avoid slopes or terrain features of concern.
Detailed Forecast
Light to moderate snow showers at cool temperatures are expected again overnight and Monday. Winds should be moderate and increase to strong in the alpine.
Light to moderate accumulations of new snow are expected and with cold temperatures this should not cause a significant increase in the current avalanche danger. Cold temperatures may help maintain older wind slab and isolated storm slab layers.
Heightened avalanche conditions are expected on specific terrain features, such as steep wind loaded slopes and steep unsupported slopes, or cross loaded features. Avalanche conditions are expected to gradually improve, however, evaluate snow and terrain carefully and avoid features or slopes of concern Monday.
Watch for firmer wind transported snow, either formed earlier or new fresh wind slabs. Older wind slabs may be masked by shallow fresh snow.
Cornices won't be listed as an avalanche problem in this area, but avoid travel on ridges, where recent cornices may have formed and avoid slopes below cornices.
Snowpack Discussion
Weather and Snowpack
The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost very strong rain crust in our snowpack.Â
A stronger than forecast storm late Monday through Tuesday deposited 2 - 2.5 ft of snow by Tuesday evening. The heavy snowfall arrived with very strong westerly alpine winds which gradually decreased on Wednesday.
Thursday began mostly sunny but increasing clouds were seen in the afternoon. SW winds above treeline increased and become were very strong Thursday afternoon, with a gust above 100 mph at 6 PM recorded at the Cascade Express weather station at Mt. Hood Meadows.
Strong southwest flow carried a strong front across the Northwest on Friday evening. At Mt Hood this caused strong southwest alpine winds, heavy, moist, dense new snow above about 4000 ft and wet snow or rain below about 4000 ft. Cooling by early Saturday deposited about 6-8 inches of new snow. Alpine winds remained very strong early Saturday with many hours of gusts over 100 mph!
Cool temperatures, light showers and moderate winds Sunday maintained current levels of avalanche danger.Â
Recent Observations
The Mt Hood Meadows patrol reported sunny but windy conditions Wednesday with windward slopes getting scoured and local size-able wind slab building on lee slopes. The lower mountain was showing signs of spring with rollerballs and small triggered loose wet avalanches.
On Thursday, NWAC observer Laura Green reported that a sun crust had formed on solar slopes. She passed along that several natural hard wind slab avalanches had occurred in White River Canyon above treeline on E-NE aspects with crown depths up to several feet. She also saw a 2-4 ft crown in Newton Canyon on a NE slope at about 6400 ft. These hard slab wind avalanches likely occurred on Wednesday.
Laura was out in Heather Canyon on Friday morning and found a reactive wind slab layer, giving moderate RP results at about 10 inches down in a pit on a NE slope at about 6450 ft. She was out later Friday on a tour in the East Fork area from 3500-5800 ft and found that the reactive wind slab layer was persisting there as well on a wind loaded slope about 10 inches down. Loose wet snow and pinwheels were seen below about 4000 ft.
MHM patrol reported large wind sculpted features in the alpine Sunday with large hard wind slabs on exposed lee slopes. Extensive explosive control failed to release these hard slabs. These hard slabs are not likely to release by human trigger, but should give caution to those traveling in steep exposed terrain.
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
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