Date issued

Nov 20, 2017 - 8:09 AM

Valid until

Nov 21, 2017 - 8:00 AM

Prepared by

ian gale

The new snow needs time to become less reactive. 

If triggered, avalanches could run to valley bottom today.

Regular season
Sunday - November 19, 2017
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.

Monday - November 20, 2017
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.

Tuesday - November 21, 2017
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

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?

Heavy snow loading and strong alpine winds have created a reactive storm slab.  Yesterday shooting cracks were observed in the alpine. The storm slab will be most reactive in unsupported terrain and features exposed to wind loading.

Travel and Terrain Advice
  • Minimize overhead exposure during periods of heavy loading from new snow, wind.
  • The new snow will require several days to settle and stabilize.

Avalanche Problem 2: Persistent Slabs

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

The Halloween Crust layer is buried down approximately 100cms. With the recent loading from heavy snow and strong winds we could see this layer become reactive. If it does "wake up" the resulting avalanches would be large!

Travel and Terrain Advice
  • Minimize exposure during periods of heavy loading from new snow and wind.

Avalanche Summary

In the Highway corridor this morning forecasters observed fresh debris to size 2.5 that ran into avalanche path runouts. There was also a report of a size 3 avalanche off of the East aspect of Grizzly Peak in the Connaught drainage. This increase in avalanche activity can be attributed to recent snow loading and strong winds in the alpine.

Snowpack Summary

Another 25cms fell overnight in the Alpine. Thats an average of 20cms's a day for the last 5 days.  This recent snow with moderate South winds has built widespread storm slabs.  The Halloween crust is the layer we're watching and it's down approx 80-100cm. The snowpack is still very thin below 1700m

Weather Forecast

Today will be a lull in the stormy weather we've been seeing. Expect a mix of sun and cloud, with no snow forecasted and freezing levels around 1500m. Wind will be light from the south.  A significant storm will affect Roger's Pass Tuesday-Thursday bringing heavy precip and very high freezing levels, up to 2800m on Wednesday!

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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