Avalanche Forecast

South Columbia

Date issued

Mar 27, 2018 - 5:11 PM

Valid until

Mar 28, 2018 - 2:00 PM

Prepared by

mgrist

Give the snow time to settle and stick to conservative terrain where there is more than 25cm of new snow. Check for how the new snow is bonding to older crusts below. Reduce your exposure to sunny slopes if the sun makes an appearance.

Regular season
Wednesday - March 28, 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 - March 29, 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.

Friday - March 30, 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?

Storm slabs are expected to remain touchy, especially in areas that saw more than 30cm of new snow into Tuesday. South and west aspects could be tricky due to buried sun crusts which could act as a good sliding layer.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Avalanche Problem 2: Loose Wet

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

Full sun on fresh snow is a recipe for avalanches. Watch for intervals of solar exposure to destabilize slabs as well as promote loose wet avalanche conditions on steeper, sun-exposed slopes.

Travel and Terrain Advice
  • Avoid exposure to sunny slopes.
  • Watch for signs the snow is moistening, such as pin wheeling and point releases below cliffs.
  • Watch for terrain traps where small amounts of snow will acumulate into deep deposits.

Avalanche Summary

A widespread natural avalanche cycle to size 2.5 was reported on Tuesday, all aspects at tree line and in the alpine.

On Monday, backcountry skiers triggered a size 2 wind slab near the Asulkan cabin on a northeast aspect near 2050m. The slab's thickness varied from 40-60cm. See the MIN report for more details.

On Sunday several natural and skier-triggered storm and wind slabs to size 2 were reported, on southeast through northeast aspects between 1900m and 2600m. Some ran on the March 18th layer, buried 25cm in that location.

On Saturday we received reports of several wind slabs and storm slabs to size 2.5, mostly on northerly aspects above 2200m. Also on Saturday, a wet loose size 1.5 avalanche injured a skier in Glacier National Park on a west aspect near 2000m.

Snowpack Summary

New amounts of (heavy) snow varied widely on Tuesday, ranging from 7 to 36 cm (with an average of about 17cm). Winds have been moderate to strong southerly with gusts to 70 Km/hr reported.

Wind slabs from late last week (thanks to south / east winds) remained reactive throughout the weekend on immediate lee features and steep roll-overs in exposed locations.

New snow amounts taper with elevation and below 1900 m, reduced accumulations have buried a supportive crust on all aspects

Isolated pockets of surface hoar (buried March 18th) have been reported between old storm snow layers on shaded aspects at higher elevations and may be found approximately 50-70 cm below the surface.

Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with a surface avalanche stepping down, large cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.

Weather Forecast

We're looking at unsettled weather with cooling temperatures until the next system arrives on Friday.

WEDNESDAY: Mainly sunny with some cloudy periods and isolated flurries. Moderate west winds 20-50 Km/hr. Freezing level to 1500 metres with alpine high temperatures around -5.

THURSDAY: Cloudy with sunny periods and flurries in the afternoon. Winds becoming light westerly. Freezing level dropping to 1200 metres with alpine high temperatures of -6.

FRIDAY: Cloudy with flurries (5-10cm snow). Light north / west winds. Freezing level 1000 metres with alpine high temperatures around -7.

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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