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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

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

Regions

Lizard-Flathead.

It's incredibly difficult to forecast what will happen with dramatic warming and sun. Potentially large cornice failure and loose wet avalanche activity is likely to be widespread, probably best to avoid avalanche terrain Monday as the snowpack feels the heat for the first time.

Confidence

Low - Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Warm air invades the region Monday pushing the temperature to near zero from valley bottom all the way up to 2500 m with just a few clouds and strong southwest wind. Tuesday and Wednesday are still warm with the freezing level hanging out around 1500 m.

SUNDAY NIGHT: Freezing level at valley bottom, moderate to strong west/southwest wind, trace of snow possible.

MONDAY: A few clouds at dawn with clear skies in the afternoon, air temperature warming to near 0 C as high as 2500 m, light southwest wind at lower elevations, strong southwest wind at ridgetop, no significant precipitation. Freezing level returning to valley bottom Monday Night.

TUESDAY: Broken cloud cover, freezing level rising from valley bottom to about 1500 m, light southwest wind at lower elevations, strong southwest wind at ridgetop, 1 to 3 cm of snow possible at upper elevations with potential for light rain down low.

WEDNESDAY: Broken cloud cover at dawn with scattered cloud cover in the afternoon, light west wind at valley bottom with strong west/northwest wind at ridgetop, trace of precipitation possible.

Avalanche Summary

On Saturday control work produced shallow size one avalanches up to 10 cm in depth. 

On Friday, a widespread natural storm slab cycle was observed as size 1.5 to 2.5 storm slabs ran.

Looking forward, solar triggering of new snow can be expected amid sun exposure and warming temperatures, especially on steep south facing slopes. 

Snowpack Summary

On Sunday a thin breakable rain crust was observed on the snow surface. Previous to this the region has received about 65 cm of snow in the last four days and almost 120 cm of snow in the last week. The recent storm snow is deep, soft and settling in the mild temperatures. Slight wind affect may be observed in exposed alpine features.

Several crust layers exist in the mid snowpack as a result of previous warming and rain events. These have not been identified as bed surfaces or failure planes in recent avalanche activity.

The bottom 10-20 cm of the snowpack consists of faceted snow and decomposing crusts. Although inherently weak, this basal layer has not been an active avalanche problem in our region for several weeks.

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Avoid exposure to sunny slopes, especially in the afternoon.

Problems

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.

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.