Avalanche Forecast

Lizard Range and Flathead

Date issued

Feb 13, 2018 - 5:07 PM

Valid until

Feb 14, 2018 - 2:00 PM

Prepared by

mgrist

Wind slabs, cornices and persistent slabs make for a tricky situation out there. Ride in conservative terrain and avoid all overhead hazard to manage your risk.

Regular season
Tuesday - February 13, 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.

Wednesday - February 14, 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.

Thursday - February 15, 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.

Avalanche Problem 1: Wind Slabs

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

Strong winds formed reactive wind slabs particularly in wind exposed areas above 1700 m for the Fernie area.

Travel and Terrain Advice
  • If triggered, the wind slabs may step down to deeper layers resulting in large avalanches.
  • Be cautious as you transition into wind affected terrain.
  • Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Avalanche Problem 2: Deep Persistent Slabs

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

Large avalanches have been running on deep weak layers. Wind loading, fragile cornices, and smaller avalanches are all possible triggers, as well as thin or rocky snowpack areas where human triggering may also be possible.

Travel and Terrain Advice
  • Extra caution needed around cornices with current conditions.
  • Be aware of the potential for large, deep avalanches.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Avalanche Problem 3: Cornices

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

Cornices have triggered very large avalanches recently. Be especially wary of long runout distances in avalanche paths, and the possibility of mature timber being taken out by a surprisingly large avalanche.

Travel and Terrain Advice
  • Avoid steep slopes below cornices.
  • Give cornices a wide berth when traveling on or below ridges.

Avalanche Summary

On Tuesday skiers were able to cut size 1.5 wind slabs on north east features at treeline. Wind slabs to size 2 were also reported, starting at the base of steep head walls.

On Saturday we received reports of impressive sizes of cornice chunks breaking off a tree line ridge feature near Harvey Pass (Flathead area), running far into the forest and meadow below. See here for photos.

On Saturday, explosive control produced wind slab results up to size 2 on north facing slopes near 2000m.

Avalanche activity on deeper layers has tapered off for now, but it's best to avoid likely trigger points such as thick-to-thin snow pack areas and also close to the base of rocky headwalls.

Snowpack Summary

Since the last snowfall almost a week ago, we've seen gusty winds (strong at times) from virtually all directions. The end result is wind slabs up to 20cm thick have formed on down wind (lee) features higher up, on a wide range of aspects.

Below 1700m, rain last Wednesday formed a thick crust and capped the snow pack.

For the past month there has been regular avalanche activity on multiple weak layers in the mid and lower snowpack. A widespread weak layer from mid December composed of facets, crusts, and surface hoar is 120-160 cm deep. Also, a rain crust with sugary facets buried in late November is near the base of the snowpack.

The take home message is that several weak layers are still lurking in the snowpack and they deserve a lot of respect. Conservative terrain use is recommended while avoiding all overhead hazard.

Weather Forecast

Wednesday will see an upslope event bringing small amounts of low density snow, followed by clearing and unsettled weather.

TUESDAY NIGHT: Flurries (5-10cm of low density snow). Winds moderate gusting strong from the north west.

WEDNESDAY: Flurries (5 -10cm accumulation). Ridge wind moderate gusting strong from the north / west. Temperature -7. Freezing level valley bottom.

THURSDAY: Sunny with cloudy periods. Ridge wind gusting moderate from the west. Temperature -9. Freezing level valley bottom.

FRIDAY: Isolated flurries. Ridge wind becoming strong from the southwest. Temperature -5. Freezing level 1000m in the afternoon.

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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