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Avalanche Forecast

Archived

Jan 13th, 2013–Jan 14th, 2013

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

Regions

South Rockies.

Increasing hazard is tied directly to the forecasted warm up.  If it doesn’t warm up until Wednesday, Tuesdays ratings are one level too high. See the forecasters blog for some ideas about the changing situation.

Confidence

Poor - Freezing levels are uncertain on Tuesday

Weather Forecast

Monday:  Mod/Strong W/NW winds at ridgetop.  Freezing level at valley bottom.  No significant snowfall.Tuesday:  Day starts out similar to Monday. Very warm air floats into the region in the afternoon.  Temps may rise above freezing at 2300m.  Little overnight recovery.Wednesday: Some lingering cold air remains in the valleys, temperatures between 1000m & 2500m rise as warm as +5c.

Avalanche Summary

Lot's of slope testing in the Lizard today, no slab releases.  Avalanche activity was limited to loose dry avalanches.

Snowpack Summary

Around 50 cm of storm snow fell in favored locations earlier this week. This snow rests on a myriad of old surfaces (January 4th interface) that include sun crust on steep south and west facing terrain, surface hoar in sheltered locations at treeline and below and facets everywhere else. The bond at this interface has tightened up and gained a lot of strength with the cold temps. Our field team didn't have any failures on this layer in their travels around Harvey Pass Friday.Wind slabs created during and just after last weeks storm have grown old and tired. The midpack is well settled and strong with one or two (location specific) crusts deep in the snowpack. These crust/facets combos are largely dormant, with the only concern being triggering from a shallow snowpack area or with a heavy trigger.

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.