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Avalanche Forecast

Archived

Feb 20th, 2016–Feb 21st, 2016

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

Regions

Mt Hood.

Watch for new building wind or storm slab layers by the end of the daylight hours if you venture out on Sunday.

Detailed Forecast

A moderate front should cause increasing winds and spread increasing snow especially to the near and above treeline at Mt Hood Sunday afternoon with a slight warming trend.

This weather should build new wind slabs on lee slopes mainly near and above treeline by the end of the day. Watch for new or previous firmer wind transported snow mainly on the lee N to SE slopes below ridges.

New storm slab is likely where more than several inches of snow rapidly accumulates Sunday by the end of the day.

A slight warming trend should help to enhance new wind and storm slab layers on Sunday.

Snowpack Discussion

Weather and Snowpack

Rain and mild temperatures dominated last Sunday and Monday forming the latest crust along the west slopes. 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 has brought about 2 feet of storm snow to Mt Hood Wednesday to today.

Storm layers may linger in the recent storm snow but will have strengthened today. Bonding of storm snow to the February 17th crust is good in some areas and not in others along the west slopes.

The mid and lower snow pack along the west slopes 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 this morning. 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.