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Avalanche Forecast

Archived

Jan 5th, 2020–Jan 6th, 2020

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 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

Lizard-Flathead.

Windslab formation has been extensive and can be found in open areas at all elevations. Avoid fat looking pockets of snow in lee features.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Sunday night: 5-10 cm of snow, moderate wind from the southwest, alpine low temperature -9 C, freezing level valley bottom.

Monday: Cloudy with sunny periods, then up to 5 cm of snow starting in the pm, moderate wind from the southwest, alpine high temperature -7 C, freezing level valley bottom.

Tuesday: 10-20 cm of snow turning to rain below 1300 m in the evening, light wind from the southwest, alpine high temperature -3 C, freezing level 1000 m rising to 1500 m.

Wednesday: 5-10 cm of snow with light rain below 1300 m, light wind from the southwest, alpine high temperature +1 C, freezing level 1500 m.

Avalanche Summary

Natural storm and wind slab avalanche activity up to size 1.5 was observed Friday and continued on Saturday, up to size 2. At least one of these was triggered by a natural cornice fall.

We are sorry to report the news of 2 fatalities in the Montana Flathead region last Wednesday. The bed surface of the deadly avalanche was a crust formed and buried around Christmas. An illustrated photo can be found here. This crust has been observed widely in the Lizard Flathead region as well, and was associated with a large natural storm slab avalanche cycle around the time of the fatalities.

Snowpack Summary

Recent snow has been blown into wind slabs in open areas at all elevations and cornice growth in the alpine has been notable. 

Several crusts layers have formed in the mid to upper snowpack as a result of recent warming and rain events. As these crusts become buried deeper, they have the potential to turn into a persistent slab problem. We'll be keeping an eye on them going forward. 

The lower snowpack consists of weak faceted snow and decomposing crusts but has not been an active avalanche problem recently.

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.

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.