Avalanche Forecast

Archived

Apr 10th, 2014–Apr 11th, 2014

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Regions

Northwest Coastal.

Winter transitions into spring! Rapid warming and intense solar radiation can increase the avalanche danger quickly. Check out the new Forecaster Blog which is directly focused on the Northern Regions.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Moderate-heavy precipitation is expected to come to an end on Friday as a strong ridge dominates the region bringing clear skies and rising freezing levels. Friday: Cloudy in the am with sunny breaks in the afternoon. Ridgetop winds light from the NW. Freezing levels rising to 1000 m. Saturday: A mix of sun and cloud. Alpine temperatures high of 6.0 degrees. Ridgetop winds light from the NE. Freezing levels near 1700 m rising to 2000 m overnight.Sunday: Mainly sunny skies. Alpine temperatures high of 8.0 degrees and freezing levels rising to 2500 m. Ridgetop winds light from the SW.

Avalanche Summary

On Wednesday, numerous naturals were reported up to size 2 from steeper start zones. I suspect with the continued snow ad strong SW winds, direct action natural storm and wind slab avalanche activity will persist through Friday. A widespread natural avalanche cycle up to size 4 occurred on Monday and Tuesday and deep persistent weak layers became overloaded, initiating very-large avalanches. In shallower snowpack areas, storm slab avalanches have stepped down to the December facet/ depth hoar layer.

Snowpack Summary

The recent storm has brought 90+ cm or more too coastal regions (80-120 mm) forming thick storm slabs and wind slabs on leeward features. At lower elevations the snowpack has become moist, wet and saturated from rain. Large cornices have formed and loom over slopes below.Several persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 -140 cm. The early February layer is down 150 - 240 cm. These layers have become overloaded and are failing in some places initiating very-large avalanches.

Problems

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.