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Mt Hood

Issued: 7:31 PM PST Thursday, February 23, 2017
by Garth Ferber

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.

Isolated lingering wind slab in the near and above treeline will continue to heal and become less sensitive to human triggering on Friday. You will need to watch for a wider variety of avalanche problems as we transition to spring. Continue to evaluate snow and terrain carefully on Friday.

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Avalanche Problems for Friday

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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Snowpack Analysis:

Weather and Snowpack

The latest of several warm, wet SW streams of moisture this season arrived on Valentine's Day 2/14, causing heavy rain, avalanches, crusts and significant snowpack consolidation through Thursday 2/16 at Mt. Hood. About 5-8 inches of snow fell at Mt Hood during the tail end of the storm.

A short period of fair weather on Friday, 2/17 caused another surface crust at Mt Hood.

A storm Sunday night and Monday tracked from the Oregon Coast across the southern Washington Cascades, depositing 10-12 inches of snow at the NWAC Mt Hood stations with a warming trend. Mid-mountain winds switched from E to W Monday afternoon and were strong W-SW above treeline for much of Monday.  

Light to moderate snowfall Tuesday changed to showers in the afternoon with moderate W winds. More light snow showers occurred Wednesday, bringing the 4 day snow total to about 2 feet at NWAC Mt Hood stations by Wednesday evening.

A mix of sun and light snow showers Thursday freshened the surface with a few inches of snow with cool temperatures and generally light winds.

Recent Observations

On Tuesday 2/21, the Mt Hood Meadows patrol triggered isolated pockets of large wind slab with explosives above treeline on lee easterly aspects. One wind slab avalanche had a crown up to 5 feet! Near treeline, 6-12” storm slab was sensitive and showed good propagation with explosives and ski cuts. Below treeline, small loose dry was the only avalanche concern on steep slopes.

The Mt Hood Meadows patrol reported isolated wind slab releases from explosive control Wednesday 2/22. These recent 6 inch to 1 foot wind slabs were above treeline on easterly facing terrain and unlikely to have released by human trigger. Shallow wet snow conditions developed during sun breaks, but no wet snow avalanches were reported.

By Thursday 2/23 more stabilizing had taken place and the Mt Hood Meadows patrol reported no results from ski test within the ski area but there was still some reactivity of wind slab layers in the 10-35 cm down on a ENE slope at 6600 ft. 

 

Detailed Forecast for Friday:

A weak low pressure system should move north to south over the Northwest coastal waters on Friday. This should trigger light occasional moderate snow showers over Mt Hood by Friday afternoon with light winds and low snow levels.

Lingering wind slabs should continue to heal, become isolated to specific terrain features, and become less sensitive to human triggering Friday. The most significant recent winds at Mt Hood were generally S-W so NW-SE aspects in the near and especially above treeline will be indicated. Watch for signs of firmer wind transported snow.

Storm slabs are expected to have stabilized by this time.

Cloudier weather should limit the potential for loose wet avalanches on Friday and this will not be indicated as an avalanche problem. Watch for wet surface snow deeper than a few inches if you find yourself on sun exposed slopes during any extended sun breaks.

Loose dry avalanches will also not be indicated as an avalanche problem. You can do tests for loose dry avalanches by pushing snow onto small safe test slopes.

Avoid areas along ridges where there may be a cornice and slopes below cornices, since cornices can fail at any time.