Avalanche Forecast

Lizard Range and Flathead

Date issued

Feb 28, 2018 - 4:57 PM

Valid until

Mar 1, 2018 - 2:00 PM

Prepared by

jmcbride

New snow has formed soft slabs at upper elevations. A strong southeast flow system will bring more snow beginning late Thursday afternoon.  Amounts are uncertain but accumulations of more than 30 cm by Friday morning may be possible in some areas.

Regular season
Thursday - March 1, 2018
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.

Friday - March 2, 2018
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.

Saturday - March 3, 2018
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

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?

New snow has formed soft storm slabs at upper elevations and winds have loaded leeward areas at ridge crest. 

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain, and avoid slopes below cornices.
  • Watch for signs of instability such as whumpfing, or cracking on small slopes.

Avalanche Summary

Tuesday a size 2.5 natural storm slab, likely triggered by a cornice collapse, was reported on a northerly aspect in the alpine. Cornice collapses up to size 1.5 were also reported but did not produce slab releases on the slopes below.

Numerous wind slabs up to size 2 and loose dry avalanches up to size 1.5 were reported from the Lizard Range on Monday running either naturally or triggered by skiers testing small slopes. Explosives triggered widespread storm slabs up to size 1.5 and size 2 results on northerly aspects. Crown depths typically ranged from 40-80 cm.

Snowpack Summary

New wind slabs are building as approximately 40-50 cm of light dry snow has fallen in recent days and is being moved around by moderate to strong westerly winds. This storm snow overlies various old surfaces including old hard wind slabs, crusts, facets and spotty surface hoar (for example February 14 surface hoar is now 50 to 70 cm below the surface).

Deeper in the snowpack, the widespread mid-December weak layer sits about 200 cm deep. This consists of a crust, facets or surface hoar.

Near the base of the snowpack, a crust/facet layer could be awoken from a thin-spot trigger point, or with a very large load like a cornice fall.

Weather Forecast

A strong southeast flow system will bring snowfall beginning late Thursday afternoon.  Amounts are uncertain but accumulations of more than 30 cm by Friday morning may be possible in some areas.

TONIGHT: Flurries. Accumulation trace. Ridge wind moderate, southwest. Temperature near -9. Freezing level lowering to valley bottom.

THURSDAY: Snow increasing in the afternoon and overnight. Accumulation 20-30 + cm. Ridge wind light to moderate, southeast. Temperature near 0. Freezing level rising to 1400 m.

FRIDAY: Mainly cloudy, flurries increasing overnight. Accumulation 2-10 cm. Ridge wind light, northeast. Temperature near -1. Freezing level 800 m.

SATURDAY: Mainly cloudy, light flurries. Accumulation trace. Ridge wind light, northeast. Temperature near -3. Freezing level 700 m.

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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