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Mt Hood

Issued: 8:10 PM PST Saturday, February 17, 2018
by Dennis D'Amico

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. 

Travel in avalanche terrain is not recommended Sunday. Moderate to heavy snowfall paired with strong winds Saturday night into Sunday morning will create very dangerous avalanche conditions especially near and above treeline Sunday. Avoid slopes steeper than 30 degrees or terrain where avalanches could release from above.

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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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Storm Slabsi

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.

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Avalanche Summary:

A strong storm system brought heavy precipitation in the form of snow, ice and rain to Mt. Hood Saturday along with moderate winds increasing to strong and gusty winds in the afternoon (WSW gusts 40-70 mph were common at the lower NWAC wind sites!). Scoured surfaces surfaces are expected on windward slopes as well as wind effected snow well into the below treeline band. Despite heavy precipitation, only about 4 inches of new snow was recorded at the Meadows and Timberline base plots through 5 pm Saturday. The rain-line is estimated to have reached near 5500 feet Saturday mid-day before cooling ensued.  

Prior to this system, 12-18 inches of storm snow fell late last week and sits on a strong firm crust layer formed earlier in the month. There are no significant layers of concern in the mid and lower snowpack.

Observations

On Saturday morning, a new rain or freezing rain crust was noted up to 6600 ft. Rime ice had covered most surfaces. Strong winds prevented observations later in the day. 

Forecast for Sunday:

Travel in avalanche terrain is not recommended Sunday. Moderate to heavy snowfall paired with strong winds Saturday night into Sunday morning will create very dangerous avalanche conditions especially near and above treeline. Avoid slopes connected to large start zones higher in the terrain where wind slab avalanches are capable of producing very large and destructive slides.

A strong cooling trend should help mitigate the storm slab likelihood, but at the same time preserve storm slab instabilities formed overnight. In non-wind affected terrain, avoid open slopes greater than 35 degrees and allow new storm slab instabilities time to stabilize. 

New snow will likely bond poorly to a slick crust that formed Saturday morning near and below treeline. This would be a likely bed surface for any avalanche that steps down to deeper layers. 

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.