Avalanche Forecast

Lizard Range and Flathead

Date issued

Dec 18, 2017 - 5:00 PM

Valid until

Dec 19, 2017 - 2:00 PM

Prepared by

istorm

Tuesday's danger ratings assume the storm gets going in the morning and is cranking in the afternoon. If the storm is delayed avalanche danger could be one level lower.

Regular season
Monday - December 18, 2017
Alpine

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.

Treeline

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.

Below 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.

Tuesday - December 19, 2017
Alpine

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.

Treeline

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.

Below Treeline

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.

Wednesday - December 20, 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

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.

Avalanche Problem 1: Storm Slabs

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

Storm snow totals of 100 or 150 cm by Wednesday. Avalanches could be large and run further than expected. It's a good time to throttle back more than you think is required and minimize exposure to overhead hazard as well as the terrain you're on.

Travel and Terrain Advice
  • Minimize exposure during periods of heavy loading from new snow and wind.
  • Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.
  • Be especially cautious as you transition into wind affected terrain.

Avalanche Summary

Natural and explosive triggered avalanche cycle reported in the Lizard Range up to size 2.5 or 3. All aspects except west facing and all elevations from 1600 m and higher.

Snowpack Summary

Monday morning dawned with up to 50 cm of fresh snow; triple what was forecast to fall overnight! Temperatures started cold and finished warmer so the storm snow is "upside down".

Prior to Sunday's storm, 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

The storm track is aligned with the Canada -- USA border; the Lizard and Flathead are in the bulls eye for Tuesday's storm.

The region received higher than forecast amounts overnight Sunday with the Lizard range showing around 50 cm of storm snow by mid-day Monday. Light snow may continue overnight Monday with less than 10 cm accumulating by Tuesday morning.

Tuesday: Snow begins again with heavy snow forecast Tuesday afternoon. Accumulations up to 35 cm are possible. Southeast or east winds with temperatures around -10 C. Snow continues overnight with another 20 to 30 cm likely.

Wednesday: Mix of sun and cloud with flurries tapering off. Cool temps in the -15 to -20 range. Light northeast wind. Storm snow accumulations from Sunday evening to Wed morning may end up in the 100 to 150 cm range.

Thursday: Mix of sun and cloud, nil precipitation, light west wind, alpine temperatures around -10 to -15 C.

Beyond Thursday is looks continued cold and dry ....

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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