Avalanche Forecast

Lizard Range and Flathead

Date issued

Dec 17, 2017 - 8:14 PM

Valid until

Dec 18, 2017 - 2:00 PM

Prepared by

istorm

Forecast Updated Monday Dec 18 at 0900. Up to 40 cm of snow overnight has increased Danger Ratings. There's a dense slab reported at higher elevations.

Regular season
Monday - December 18, 2017
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

Tuesday - December 19, 2017
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Wednesday - December 20, 2017
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

40cm snowfall overnight Sunday.
Continued winds Monday are expected to form fresh sensitive wind slabs that will be most prevalent immediately below ridge crest and behind mid slope terrain features.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be cautious as you transition into wind affected terrain.
  • Use caution on open slopes and convex rolls

Avalanche Summary

Monday Morning UPDATE: Explosive triggered avalanches to size 2.5

No new avalanches observed on Sunday. On Friday and Saturday small sluffs and soft slab avalanches were reported to size 1.

Please submit your observations to the Mountain Information Network.

Snowpack Summary

The region was hit hard by wind over the weekend, but there may be protected areas where up to 10cm of new low density snow survived. At or just below the surface there is a wide range of conditions. Windward slopes have been scoured down to the old rain crust and/or rock. Sun and temperatures crusts have formed on south through west facing slopes. In sheltered terrain at and below treeline, large feathery surface hoar and sugary facets exist. Roughly 30 to 60cm below the surface you should be able to find a hard crust that was buried near the end of November. This crust is approximately 30cm thick and extends from 1600m to mountain top on all aspects. Below this crust, the snowpack is moist to ground. Average snowpack depths at treeline in the region range from 70 to 110cm.

Weather Forecast

Zonal flow should be firmly established by Monday morning. Two pulses established within this flow are expected to deliver modest quantities of snow and wind to the Lizard and Flathead ranges through Tuesday evening. The models currently show 5 to 10cm for each 12 hour period between Monday morning and Tuesday night, but there is potential to double these amounts on Tuesday. Stay tuned for more details.

UPDATE MONDAY MORNING: 40 cm of snow arrived overnight in the Lizard Range, triple the amount originally forecast.

MONDAY: Overcast, freezing level starting at 600m rising to 1000m in the afternoon, moderate to strong southwest wind, 2 to 10cm of snow possible.

TUESDAY: Overcast, freezing level near valley bottom, light variable wind at valley bottom, potentially strong southwest wind at ridge top, 5 to 20cm of snow possible.

WEDNESDAY: Overcast with some clearing in the afternoon, freezing level at valley bottom, light variable wind, 1 to 5cm of snow possible.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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