Avalanche Forecast

Archived

Apr 9th, 2014–Apr 10th, 2014

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

Olympics.

The main concerns will be wet loose avalanches and cornice failures on Thursday.

Detailed Forecast

Mostly sunny weather and warmer temperatures should be seen on Thursday. A weak system should begin to move to BC Thursday night. Some mid or high clouds may be seen over the Olympics and north Cascades late Thursday afternoon.

The sun is getting much stronger now that we are well into April. The most extensive concern should be possible wet snow avalanches on solar slopes ATL but this is possible on other slopes as well. Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches. Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences.

Cornices will be listed as a secondary concern due to the recent failures, warmer temperatures on Thursday and that this is the time of year they become active. Avoid walking onto or below cornices - many have grown large recently. Cornices often break back further from the edge than expected and trigger avalanches on slopes below.

Snowfall from the last weaker front was not deep or extensive and wind slab and storm slab will not be listed as concerns. But continue to watch for firmer wind transported snow or deeper recent snow in the upper ATL areas.

Snowpack Discussion

Fronts crossed the Northwest Friday and later Saturday. Water and snowfall for these systems at Hurricane was about .7 and 5 inches respectively. Warm temperatures were seen by Sunday and especially Monday.

NWAC observer Katy Reid observed mashed potato snow, natural pinwheeling and increasing ski penetration into wet surface snow Sunday afternoon. She reported shallow wet loose avalanches below treeline, but found one larger (D2) wet loose avalanche on a steeper NE aspect below treeline (see picture below). Digging around on different aspects near and below treeline, she found the saturated upper snow (15-50 cm) overlying a hard melt-freeze crust to be un-reactive in snowpit tests. No reports were available Monday, but warmer temperatures and sunshine likely led to additional wet snow avalanches. Cornices have grown large over the last few weeks.

Wet loose avalanche near Maggie's Bowl at Hurricane Ridge on Sunday by NWAC observer Katy Reid.

A weaker front moved east over the Northwest Tuesday afternoon and night. A weak short wave and colder air mass followed the front Tuesday night. No new reports are available today but more natural or triggered wet loose avalanches seem likely on solar slopes.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.