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Avalanche Forecast

Archived

Nov 30th, 2016–Dec 1st, 2016

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

Recent wind slabs may linger Thursday, but slowly stabilize. Also, watch for  local cornices along ridges. Be prepared to alter plans if local snow and avalanche conditions warrant. 

Detailed Forecast

Another break between systems is expected Thursday as brief high pressure transits the region. There may be a few showers early Thursday to midday, but little accumulation is expected. Winds should be light Thursday.

This should allow for recent storm snow and any wind slabs below ridges to begin settling.  The greatest concern Thursday should be on steep lee slopes below ridges that may have wind transported snow deposited Wednesday. These slopes should range from NW-SE facing. 

In addition, watch for any recent cornice formations along ridges and give these early season cornices a wide birth as they may be fragile.   

In much of the lower elevation, below treeline band, there is insufficient snow to produce avalanches, but watch for early season hazards such as rocks and creeks.  Avalanche problems should be limited to the upper part of this elevation band and higher elevations.

Snowpack Discussion

Weather stations on Mt. Hood picked up 11 and 15 inches at Timberline and Mt. Hood Meadows respectively through early Monday morning. Another 7 to 9 inches fell during heavy showers through Monday evening. W to NW winds remained moderate on Monday helping to transport new snow to lee easterly aspects. 

The Mt. Hood Meadows pro-patrol found sensitive, but soft 6-12" storm slabs on most aspects Monday morning failing within the new storm snow.  Wind slabs averaged 18" on north aspects above treeline with a crust for a bed surface that formed during a warm-up last Friday. 

On Tuesday, Mt. The hood Meadows patrol found shallow storm slabs near and below treeline generally unresponsive to ski cuts and explosives.  However, evidence of two larger natural wind slab avalanches was observed in White River Canyon, on E-SE aspects, both with start zones around 7000'. One stepped down to deeper layers. 

By Wednesday afternoon, another 6-8 inches of storm snow had been deposited through the day along with moderate ridgetop winds.

Storm snow has been right side up, with previous storm snow settling and stabilizing quickly, limiting the avalanche hazard to the most recently deposited layers.

In general the below tree-line elevation band has plenty of terrain anchors and offers lower avalanche potential due to the shallow snowpack. 

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.