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Mt Hood

Issued: 7:48 PM PST Saturday, March 18, 2017
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.

The avalanche danger should decrease Sunday as a wet snowpack refreezes. Fresh wind slab will mostly likely be found above treeline. Shallow loose wet slides are likely on steeper solar aspects in the afternoon. 

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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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Snowpack Analysis:

Weather and Snowpack

The first week or so of March was very cool and snowy.  NWAC stations at Mt Hood piled up about 6-7 ft of snow.

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately these systems delivered far more rain than snow. At least two regional avalanche cycles occurred during the stretch. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. 

After a short respite from the active weather pattern on Thursday, another strong low pressure system brought about an inch of predominately rain to the NWAC Mt. Hood stations Friday night and Saturday morning. Rapid cooling late Saturday morning was followed by snow showers with light new snow accumulation. Strong W-SW winds were transporting new snow above treeline by mid-day Saturday. 

Recent Observations

By Thursday at 6600 ft the MHM reported 4-8 inches of recent snow over deep wet consolidated snow. Laura Green also reported a cornice caused a small slab in the lower White River Canyon.

Mt. Hood Meadows pro-patrol reported a switch to snow at mid-mountain by noon Saturday with strong W-SW winds beginning to build fresh new wind slab above treeline. 

Detailed Forecast for Sunday:

Decreasing snow showers along with rapid cooling Saturday night through Sunday morning should transition to mostly sunny skies by Sunday afternoon. Freezing levels will be on the cool side Sunday but late March sunshine will help bump up temperatures to near or above freezing at lower and mid-elevations. Winds are forecast to be fairly light on Sunday.

The avalanche danger should decrease Sunday as a wet snowpack refreezes.

Fresh wind slabs have likely built on NW to SE aspects, mainly above treeline. Watch for firmer wind transported snow on other aspects, especially in areas of complex terrain. All aspects will be listed until more information is received on recent general loading patterns. 

Generally small loose wet avalanches are likely at lower elevations and on solar slopes. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases.

Although the likelihood of wet slab or glides avalanches has greatly decreased with the cooling trend, these avalanche problems may still occur 24 to 48 hours following a heavy rain event. Continue to avoid unsupported slopes, especially where you know there is a smooth underlying surface or slopes with glide cracks. Wet slab or glide avalanches will not be listed as an avalanche problem in the Mt. Hood area due to less rainfall than other areas in the Cascades. 

It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.

No Corresponding Mountain Weather Forecast Available