Avalanche Forecast

Sea To Sky

Date issued

Feb 2, 2018 - 5:52 PM

Valid until

Feb 3, 2018 - 2:00 PM

Prepared by

mgrist

Snow totals are very uncertain in this weather pattern. Danger ratings are based on the higher forecast amounts of snow. New snow may add to wind slabs caused by extreme winds from Friday.

Regular season
Friday - February 2, 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.

Saturday - February 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

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

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.

Sunday - February 4, 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

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.

Avalanche Problem 1: Storm Slabs

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

Areas with high amounts of new snow could be primed for storm slabs whereas areas that see less snow may be more susceptible to wind slabs.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation.
  • Stay off recent wind loaded areas until the slope has had a chance to stabilize.

Avalanche Problem 2: Cornices

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

Recent heavy snowfall and high winds have formed fragile new cornices. These monsters may surprise with nasty consequences. Use extra caution around ridge crests.

Travel and Terrain Advice
  • Give cornices a wide berth when travelling on or below ridges.
  • Falling cornices may trigger large avalanches on the slopes below.

Avalanche Summary

On Friday ski cutting produced several size 1 soft slabs on immediate down wind (lee) features.

Explosives control on Thursday and Friday triggered cornices at ridge crests, mostly Size 1.5 - 2.

Looking forward, light amounts snow and strong winds on Friday are expected to promote a new round of wind slab activity in higher elevation lee terrain.

Snowpack Summary

On Friday morning only 3-5cm of new snow had fallen overnight as temperatures warmed up to +1 at tree line. Winds, however, were strong to extreme from the south (gusting to 121 Km/hr at the peak of Whistler) and created fresh wind slabs in exposed downwind (lee) terrain. At lower treeline and below, generally light amounts of snow now overlie a melt-freeze crust which formed during last Monday's warm storm.

The new snow adds to the 170cm of snow that fell during the last few weeks of January. These series of storms were accompanied by strong to extreme winds which resulted in extensive scouring and impressive cornice growth in upper elevation terrain. These accumulations sit on a crust from mid-January which generally shows signs of bonding to the overlying snow; however, it has the potential to "wake-up" with a large trigger such as a cornice fall.

Below this, the snowpack is thought to be generally strong and well-settled.

Weather Forecast

Saturday: Snow (5 - 20cm possible) / Light to moderate westerly winds / Freezing level 1800m dropping to 1000m in the afternoon.

Sunday: 5-25cm of new snow / Moderate southwest winds / Freezing level at 1500m

Monday: Isolated flurries / Light north westerly winds / Freezing level at 1400m

Note: Confidence is low for forecast wind values and precipitation amounts on Saturday and Sunday.

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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