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Avalanche Forecast

Archived

Dec 19th, 2020–Dec 21st, 2020

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

Regions

Yukon.

My primary concern is wind slabs behind ridges, ribs, and rolls. My second concern is the warm temps turning the snow "upside down" -- if the snow is warm & dense at the surface, cold and soft below increase caution on steeper rolls irrespective of aspect or wind effect.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Even if the days are short, sunny weather is returning.

SATURDAY NIGHT Light snow ending overnight. Southerly winds lighter at lower elevations, moderate to strong up high. Temps near zero in White Pass

SUNDAY: Clearing sky, no new snow, cooler temps around -5 to -10 C near White Pass, continued light to moderate southwest winds.

MONDAY: very similar to Sunday, just a touch cooler with temps around -10 C near Whitepass.

TUESDAY: no new snow, moderate southerly winds, continued -5 to -10 C temps with a mix of sun and clouds.

Avalanche Summary

There have been no recent reports of avalanches in the region. The only reports we've received are of exceptional powder riding.

The most likely place to trigger an avalanche is on the leeward side of a ridges and ribs where new wind slabs were formed.

Snowpack Summary

Snowpack is 200 cm in Whitepass, closer to 100 cm in drier areas like the Wheaton.

Eight to ten hours of moderate to strong southwest winds overnight Friday & early Saturday morning build wind slabs and cornices; the key question is how widespread and sensitive the upper snowpack is.

Below this surface snow lies a widespread melt-freeze crust. The crust has been reported up to 1400 m in the Wheaton Valley, up to 1800 m near the Alaska border. 

The lower snowpack is generally settled and strong after a massive storm at the beginning of December. However, there is potential for weak snow at the bottom of the snowpack in colder drier areas such as the Wheaton Valley. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.