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Avalanche Forecast

Archived

Feb 22nd, 2017–Feb 23rd, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Lingering wind slabs, will continue to heal, becoming less sensitive to human triggering. Caution in steep terrain at higher elevations, that may have received recent wind transported snow. Watch for any wet snow conditions developing during extended sun breaks. 

Detailed Forecast

Thursday should remain cool with sunbreaks and scattered snow showers, mainly in the afternoon. Very light new snow is expected, if any. 

Lingering wind slabs should continue to heal and become less sensitive to human triggering Thursday. Wind slabs should be confined to specific terrain features, more likely on N-E-S aspects near and especially above treeline. 

Storm slabs will not be listed as an avalanche problem Thursday as they continue to strengthen and bond. 

Loose wet avalanches may be possible on steep sun exposed terrain. Watch for wet surface snow if you find yourself on sun exposed slopes during extended sunbreaks.

Snowpack Discussion

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 tracked from the Oregon Coast across the southern Washington Cascades, depositing 10-12 inches of snow on Mt. Hood stations Sunday night and Monday along with a warming trend that peaked late Monday morning. Mid-mountain winds switched from easterly to westerly 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 westerly transport winds. More light snow showers occurred Wednesday, bringing the past four day snow total to about 2 feet at Mt. Hood stations by Wednesday evening.  

Recent Observations

NWAC pro-observer Laura Green was out on Sunday at Bennett Pass up to about 6000 feet and found recent snow well bonded to the 2/17 crust and observed no signs of avalanches. The Mt Hood Meadows pro-patrol on Sunday found N-E slopes up to about 6600 feet a bit loaded with 8-10 inches of wind transported snow on the 2/17 crust but no significant wind slab.

On Tuesday, Mt. Hood Meadows 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. 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.  

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.