Avalanche Forecast

Cariboos

Date issued

Jan 17, 2018 - 4:41 PM

Valid until

Jan 18, 2018 - 2:00 PM

Prepared by

ghelgeson

This warm, wet and windy storm is expected to form a touchy slab that rests on crust and surface hoar. There is potential for rain as high as 1700 m and winds will quickly form potentially deep slabs. Choose simple objectives without overhead hazard.

Regular season
Wednesday - January 17, 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.

Thursday - January 18, 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

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.

Friday - January 19, 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

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.

Avalanche Problem 1: Storm Slabs

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

By Thursday morning a slab 5 to 20 cm in depth should rest on the old surface which is a combination of crust and surface hoar. The new snow is expected to be quite touchy and sensitive to human triggering as a result.

Travel and Terrain Advice
  • Carefully monitor the bond between the new snow and old surface, touchy slabs are expected.
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Be very cautious as you transition into wind affected terrain.

Avalanche Problem 2: Persistent Slabs

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

As new snow begins to stack up we can't forget about the persistent weak layers lurking in our snowpack that remain quite capable of producing very large avalanches. Keep the terrain choices reigned in as the snowpack adjusts to the new load.

Travel and Terrain Advice
  • Storm slabs in motion may step down producing large destructive avalanches.
  • Numerous large avalanches have run on these layers in well supported, treed terrain.
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.

Avalanche Summary

No new avalanche activity to report from Tuesday.

On Monday warm temperatures and direct solar induced natural persistent slab avalanches to size 3.0 on solar aspects between 1600 and 2600 m. Loose wet avalanches were reported from all aspects to size 2.0.

On Sunday loose avalanches were reported from all aspects to size 1.0. On Southwest, south and southeast facing terrain between 1500 m and 2700 m, loose wet avalanches to size 2.5 and persistent slab avalanches to size 2.0 were reported to have failed naturally. A small wind slab was human triggered on a north facing feature just below ridge crest.

On Saturday natural avalanches up to size 2.5 were reported on northeast facing features between 1200 m and 1500 m. One small skier triggered avalanche was remotely triggered on a moderately inclined northeast facing alpine feature.

Snowpack Summary

Spotty freezing rain Tuesday may have left a slight "glaze" on the surface which adds to the crust that is being widely reported from many locations, high elevation north is likely one of the few crust-free zones. Fresh surface hoar up to 10 mm in size has been reported to ridgetop . We can probably expect a touchy storm slab to form on this interface as storm totals exceed 10 cm.

There are two significant and active Persistent Weak Layers (PWL) that we are monitoring.

The first PWL is known as the early January interface, it is 20 to 60 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is present at all elevation bands. Recent snowpack tests have shown easy to moderate planar results at this interface.

The second PWL is the mid-December facet/surface hoar/crust combination that is now buried 50 to 80 cm deep and is most problematic at and below treeline. This interface is not thought to be present in the alpine. This interface has shown sudden collapse in recent snowpack tests with easy to moderate loads.

The November rain crust down 70 to 100 cm is thought to have gone dormant for the time being.

Weather Forecast

A classic winter storm smashed into the coast Wednesday morning and that system spilled into the interior Wednesday afternoon.  By Wednesday night strong southwest flow aloft will allow the freezing level to rise to around 1700 m as waves of convective precipitation move through the region.  Snowfall should persist into Thursday and the freezing level is expected to fall back towards valley bottom Thursday night.  Friday and Saturday look cool and calm with another system set to move into the interior on Sunday. 

WEDNESDAY NIGHT: Freezing level between 1500 and 1700 m, 2 to 10 cm of snow across the region, favored convective pockets could see 15 cm or more, strong south/southwest wind. 

THURSDAY: Broken cloud cover, freezing level around 1200 m, strong southwest wind, 1 to 5 cm of snow, favored convective pockets could see 10 cm or more.

FRIDAY: Scattered cloud cover, freezing level beginning at valley bottom rising to around 1300 m in the afternoon, light to moderate southwest wind, no snow expected.

SATURDAY: Scattered cloud cover, freezing level holding near valley bottom, light south/southwest wind, 1 to 5 cm of snow possible.

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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