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Avalanche Forecast

Archived

Apr 19th, 2013–Apr 20th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to limited field observations

Weather Forecast

An upper trough will move through the Interior tomorrow. The NW flow will bring cooler, dryer air to the region with some pulses of precipitation. Saturday: Overcast with some clearing in the most northern parts of the region later in the day. Light-moderate precipitation amounts. Ridgetop winds blowing moderate from the NW. Freezing levels near 1600 m.Sunday/Monday: A ridge of high pressure will bring a mix of sun and cloud, with cooling and dryer conditions. Freezing levels will be near 1200 m during the afternoon and falling to valley bottom overnight.

Avalanche Summary

No new avalanche activity has been reported.

Snowpack Summary

Up to 15 cm of new snow sits on a variety of old surfaces. These include melt-freeze crusts on solar aspects and dry snow with some surface facts and surface hoar on Northerly aspects. Wind slabs have built on lee slopes and behind terrain features. Cornices are huge and threaten slopes below.Deeper in the snowpack (60-120 cm down) a weak interface exists which consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Earlier this week, very large avalanches were reactive on this interface in the neighboring Glacier National Park. I would practice caution and remain suspicious of high alpine steeper slopes.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.