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Avalanche Forecast

Archived

Feb 22nd, 2016–Feb 23rd, 2016

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.

Regions

Mt Hood.

Watch for new or previous firmer wind transported snow on a variety of aspects Tuesday: Don't let the combination of Moderate avalanche danger with non-traditional lee aspects/cross-loaded slopes catch you by surprise! 

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

Last week, heavy rain and mild temperatures dominated along the west slopes including Mt. Hood forming the latest rain crust. NWAC sites at Mt Hood recorded about 2.5 inches of rain over the 2 days ending Tuesday morning February 16th.

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 from Wednesday through Saturday morning. A weak front on Sunday only brought a few inches of additional snowfall through Monday morning.

Storm layers in the snow received from Wednesday to Saturday should be strengthening. Bonding of storm snow to the February 17th crust varied along the west slopes and Mt. Hood initially, but should have also improved over the last few days.  

The mid and lower snow pack along the west slopes and Mt Hood should be a stable mix of crusts and layers of moist or 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 Saturday. 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.

Several reports from the Mt. Hood pros on Monday indicated a generally stable snowpack with minimal sun affects on solar slopes and some scoured windward slopes above treeline due to the persistent westerly transport winds. 

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.