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Mt Hood

Issued: 6:00 PM PST Saturday, April 29, 2017
by Kenny Kramer

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

NWAC Spring Forecast Schedule

The NWAC issued daily mountain weather and avalanche forecasts through Saturday, April 15th. Mountain weather and avalanche forecasts will be issued during the spring transition April 20-22nd and April 27-29th. Weekend outlooks will be issued Thursdays, May 4th, 11th, 18th and 25th.

Special advisories, watches and warnings will be issued throughout the spring for unusual or dangerous avalanche conditions. You can find out what constitutes a special advisory, watch or warning here.

Avoid steep, exposed wind loaded terrain above treeline where fresh wind slabs may be reactive to human trigger Sunday. Watch for wet and weak surface snow from daytime warming and any afternoon sunshine. Continue to give cornices a wide berth if traveling along ridge-lines and avoid slopes below cornices. 

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Avalanche Problems for Sunday

Wind Slabi

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.

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Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

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Cornicesi

Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.

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Snowpack Analysis:

A cool, snowy pattern has been seen in late April mainly for the Cascade west slopes and especially for the Mt Hood area.

Last week from Monday 4/17 to Thursday 4/20 the NWAC weather stations at Mt Hood picked up 1 - 2 inches of WE. Much of this WE fell as snow above about 6000 feet.

A fair day was seen last Friday with most NWAC stations in the Olympics and Cascades reaching the 40's and 50's.

The most recent storm cycle began a week ago Saturday. In the 6 days ending Friday morning, 4/28 the NWAC stations at Mt Hood had 4-6 inches WE, with an average snowline from 5500-6000 feet! 

Much of this storm snow has settled to about 3-6 inches below treeline by Saturday, but amounts of 1-2 feet remain in areas above treeline! 

Recent observations

NWAC observer Laura Green did a short tour at the closed Meadows ski area on Monday and turned in an observation via the NWAC Observations page. In windy conditions she visited E-SE slopes in the below tree line. She found wind loading to E slopes and about 12 inches of rapidly accumulated snow that was resulting in touchy storm slab and a high danger.

Observations from the Mt Hood Meadows patrol Friday indicated there was a period of sub freezing rain recently, forming a clear ice layer up to about 7300 feet. As a result, wind slabs were isolated, but some hard slabs of 1-3 feet were released with explosives above treeline on wind loaded terrain. No slabs were reactive to human trigger Friday. 

Detailed Forecast for Sunday:

A front is expected to move across the Mt Hood area Saturday night. This should cause a period of moderate rain and snow with snow levels about 6000-6500 feet and a period of strong SSW winds. Showers should taper Sunday and end with gradual clearing late Sunday. Wind should shift to westerly and diminish through the day Sunday. 

Some shallow fresh wind slabs are likely on lee slopes, mainly NW-SE facing above treeline by early Sunday.  Watch for and avoid areas of firmer wind transported snow on NW-SE aspects and other cross loaded features on other aspects in areas of varied terrain.

Near and below treeline, cooling should allow for previously wet surface snow to begin re-freezing, diminishing the threat of loose wet slides. However, watch for wet surface snow deeper than a few inches, pinwheels and initial small loose wet avalanches that indicate the potential for loose wet avalanches.

Cornices are still large, so give them a wide safety margin. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give potential cornices a wide berth if traveling along ridge-lines and avoid slopes below cornices. See a blog post regarding cornices here.

Avoid unsupported slopes with overhanging blocks of snow and smooth rock underneath. Glide avalanches are difficult to predict and can release at any time, not just during the heat of the day.

Note that this forecast applies up to the Cascade crest level and does not apply to higher elevations on the volcanoes.