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Avalanche Forecast

Archived

Feb 21st, 2016–Feb 22nd, 2016

Alpine
Natural avalanches possible, human triggered probable.
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.

The avalanche danger should gradually decrease on Monday. Watch mainly for new or previous wind slab on the lee slopes near ridges or mid-slope where cross loading may have occurred.

Detailed Forecast

West winds and snow showers following the front should taper off on Monday with lower snow levels. The avalanche danger should gradually decrease on Monday.

The winds and snow Sunday and Sunday night may have built new shallow wind slabs on lee slopes mainly near and above treeline by the end of the day. Older wind slab may linger on similar slopes. Watch for new or previous firmer wind transported snow mainly on the lee N to SE slopes near ridges or mid-slope where cross loading may have occurred.

New shallow storm slab is possible if you are in an area where more than several inches of snow rapidly accumulated Sunday to Monday morning.

Snowpack Discussion

Weather and Snowpack

Rain and mild temperatures dominated last Sunday and Monday forming the latest crust along the west slopes and Mt Hood. NWAC sites at Mt Hood recorded about 2.5 inches of rain over the 2 days ending Tuesday morning.

An active and at times stormy, cooler pattern began to bury the crust on February 17th and brought about 2 feet of storm snow to Mt Hood Wednesday to Friday. Another front is crossing the area on Sunday followed by a short wave Sunday night that will generally cause shifting winds and a few inches of snow.

Storm layers in the snow from Wednesday to Friday at Mt Hood should be strengthening. Bonding of storm snow to the February 17th crust has been good in some areas and not in others along the west slopes.

The mid and lower snow pack along the west slopes and Mt Hood should be a stable mix of crusts and layers of wet rounded snow crystals.

Recent Observations

NWAC pro-observer Laura Green was in the Newton and Clark Canyon areas on Thursday increasing windy and snowy weather. She reported building wind and storm slab of 8-10 cm with easy hand shears on the February 17th crust.

The Mt Hood Meadows pro-patrol reported large explosively triggered 2-3 foot hard wind slab on north to east slopes in the above tree line Satuday. In the near and below treeline storm snow was well bonded to the February 17th crust with some small easily triggered storm slab on isolated terrain features.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.