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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 2021

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

Regions

Lizard-Flathead.

There is uncertainty with localized forecast snowfall amounts. A mix of recent storm snow and strong winds will likely combine to make slabs sensitive to human triggering on Monday. Be especially cautious transitioning into wind affected terrain and steer clear of cornices.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

There is some weather uncertainty. There are two opportunities for "enhanced" local precipitation amounts in various places in our vast region. The first chance comes with the strong south west flow into this evening. The second comes with the potential for localized convective activity with the passing of the cold.

SUNDAY - Snow, 10-20 cm (up to 25 cm in some locations) / strong southwest wind, switching to northwest as could front passes / low -5 / freezing levels dropping back to valley bottom.

MONDAY - Snow tapering off in the morning / sunny periods possible / strong north west wind easing in afternoon / alpine high temperature near -3 

TUESDAY - A mix of sun and cloud / light to moderate west wind / alpine high temperature near -5 / freezing level 1500 m

WEDNESDAY - Mostly clear / moderate southwest wind / alpine high +2 / freezing level above 2000 m

Avalanche Summary

On Sunday there were some small wet loose avalanches out of alpine features. 

On Saturday there were small wet loose avalanches and a natural cornice fall reported in the Lizard Range.

On Friday, there were a few reports of size 1 human triggered storm slab avalanches on north aspects in the alpine.

Glide cracks continue to grow. This serves as a great reminder to avoid slopes with glide cracks on them at all times. They are inherently unstable and can release at any time.

Snowpack Summary

By Monday in sheltered areas expect 10-30 cm of recent storm snow over a variety of old surfaces such as crusts on all but north aspects in the alpine and treeline and crusts at all elevations below 1700 m. 

Recent winds have switched from strong southwest to strong northerly so fresh and reactive wind slabs may be found on a variety of aspects in open terrain in the alpine and treeline.

Lower elevations are likely to be crusty and rugged when freezing levels drop Monday morning.

The mid-pack and lower snowpack is generally well settled and strong.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Carefully monitor the bond between the new snow and old surface.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.

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.