Avalanche Forecast

Lizard Range and Flathead

Date issued

Jan 13, 2018 - 3:03 PM

Valid until

Jan 14, 2018 - 2:00 PM

Prepared by

istorm

A Special Public Avalanche Warning is in effect for this region. With a tricky snowpack and large avalanches triggered on low-angled and treed slopes Travel In Avalanche Terrain Is Not Recommended.

Regular season
Saturday - January 13, 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

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.

Sunday - January 14, 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

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.

Monday - January 15, 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

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.

Avalanche Problem 1: Storm Slabs

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

Many avalanches have been naturally and human-triggered in the recent 100+ cm of snow. Incoming warm air temperatures should increase the likelihood of triggering. If triggered, storm slabs could step down to deeper persistent weak layers.

Travel and Terrain Advice
  • Use caution when entering lee areas. Recent wind loading may have created wind slabs.
  • Avoid exposure to terrain traps where the consequence of any avalanche could be serious.
  • Avoid exposure to overhead avalanche terrain. Large avalanches may reach the end of run out zones.

Avalanche Problem 2: Persistent Slabs

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

Large avalanches are being triggered on buried weak layers, even in fairly dense trees and shallow slope angles, including remotely triggered slides. These layers are touchy and can produce very large, destructive avalanches that run far.

Travel and Terrain Advice
  • Travel in avalanche terrain is not recommended with current conditions.
  • Avoid lingering or regrouping in runout zones.

Avalanche Summary

Friday reports were of intentionally triggered small avalanches on small & low consequence "test slopes, larger (size 2.5 explosive triggered slides) and most interestingly (importantly) remotely triggered avalanches from 20m away. On Saturday a larger avalanche was triggered with explosives running on the November crust down 100 to 200 cm. This was a size 3.5 slide that ran nearly 800m and exceeded the path's historic runout distance.

Snowpack Summary

The snowpack remains near a tipping point. Cooler temperatures Friday and Saturday reduced the sensitivity slightly but forecast warming should bring us back closer to the balance point.

Over 100 cm of snow fell within the past week.  The snow fell relatively warm with moderate winds, which formed storm slabs.  The snow also formed large cornices.  This storm snow sits on variable feathery surface hoar in the region.  Deeper in the snowpack, an unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations.  Below, a rain crust that developed late-November with associated sugary facets are also being stressed. Snowpack test results show sudden fracture characters and high propagation potential for all of these buried layers, indicating that they can be triggered and could propagate into large, destructive avalanches. This has been the case, as shown in the Avalanche Summary.

Weather Forecast

Saturday and Saturday Night:  Cloudy, flurries, little wind ... not much of significance ... however a warm ridge is approaching which means a temperature inversion with warm temperatures at treeline and alpine elevations will devolop over the next few days.

SUNDAY: Mix of sun & cloud and the temperature inversion could mean valley fog with sunshine above. Treeline and alpine temperatures just below zero. Light northerly winds.

MONDAY: Mostly sunny with some low level (valley) cloud. Light and variable wind. Warmest temperatures at treeline and alpine elevations near zero.

TUESDAY: Treeline and alpine temperatures just above zero. Wind becoming more westerly as the next pacific system approaches.

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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