Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
jcoulter,
Avalanche Canada
A new storm with intense loading rates is set to hit the region by Monday afternoon and continue overnight. Danger ratings may rise to HIGH by late afternoon. Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
Summary
Confidence
Weather Forecast
SUNDAY NIGHT - Trace to 5 cm / moderate west wind, alpine low temperature near -8
MONDAY DAY - Snow increasing later in the day 10-15 cm, moderate west wind / alpine high temperature near -5
MONDAY NIGHT - 15-30 cm / south east gusty wind / alpine high temperature near -3
TUESDAY - Morning flurries up to 5 cm / windy at times / alpine high -7
WEDNESDAY - Clearing, light west winds, alpine high -9
Avalanche Summary
On Sunday the South Rockies Field Team experienced lots of whumpfing and remote triggered a size 2 avalanche in a low snowpack area. The failure plane was facets on the early December persistent weak layer, even though there was no crust at that elevation (2100m). They also saw recent natural avalanche activity up to size 2.5. Alpine and open treeline features most exposed to wind produced the most avalanche activity.
On Saturday a natural size 2.5 avalanche was spotted out of extreme, shallow, rocky, wind affected terrain in the Crowsnest Pass. It was thin, but propagated widely. The date of the event was uncertain.
Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
After a break overnight, we will see increasing snowfall amounts on Monday afternoon forming new storm slabs. Slabs are especially reactive in areas where they have been stiffened even slightly by wind.
This recent snow means there is now 40-60 cm above the early December weak layer. There may be weak faceted grains and/or a crust making it susceptible to human triggering and step down avalanches from recent storm snow.
The base of the snowpack consists of a hard melt-freeze crust from early-November that may also have weak crystals around it. There has not been recent avalanche activity on this layer but it remains on our radar. The most likely spot to trigger it would be on thin and rocky slopes.
Snowpack depths vary substantially in the region with the average snowpack depth at treeline being approximately 90-140 cm.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Problems
Storm Slabs
The snowpack isn't getting much time to adjust to recent snowfalls as a new wave of precipitation is set to hit the region Monday afternoon. Open areas that are more exposed to wind have been producing more avalanches. Simple, low angle terrain away from overhead hazard is a good choice right now.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
This layer has reached a tipping point in parts of the region. 40-70 cm of snow currently sits above a weak layer from early December. Combinations of sugary facets , surface hoar and/or a crust mean persistent slabs are likely reactive, especially to human triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
