North Rockies Avalanche Forecast

Feb 19th, 2020 5:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs, Cornices and Persistent Slabs.

Conditions have really improved & it's largely about two things now: avoiding wind slabs at upper elevations and staying away from cornices which continue to fail naturally in somewhat spectacular form.

Summary

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

The later half of the week features plenty of periods of sun along with potential for some pretty intense wind.

WEDNESDAY NIGHT: Strong southwest wind, freezing level at valley bottom, no significant precipitation expected.

THURSDAY: Scattered cloud cover, strong west/southwest wind, freezing level rising to about 1200 m during the day, no significant precipitation expected.

FRIDAY: Broken cloud cover, strong southwest wind, freezing level rising to about 1400 m, no significant precipitation expected. Potential for 5 to 10 cm Friday night.

SATURDAY: Broken cloud cover at dawn, clearing throughout the day, moderate to strong west/northwest wind, freezing level near valley bottom, trace of snow possible.

Avalanche Summary

Given that there has been 50 to 100 cm of storm snow in the last week with quite a bit of wind, surprisingly little slab avalanche activity has been reported. Cornices are a different story, there have been quite a few reports of size 2.5 cornice releases from the last few days, a trend that is expected to continue through the forecast period with the sun making a rather prominent appearance.

Snowpack Summary

Dribs and drabs of snow from the last few days add to last week's phenomenal storm that produced 50 (Kakwa) to 100 (Torpy) cm of storm snow under mild temperatures and moderate wind from the south, southwest and southeast. Most of the observations we're seeing suggest that the copious amount of storm snow arrived warm and it continues to settle out nicely. The storm snow still has has very little slab property, but we're short on observations from more wind effected terrain.  

The presence of buried surface hoar about 40 to 60 cm below the surface has been confirmed in the Pine Pass, Torpy & Renshaw zones, it may be more widespread throughout the region too. If you're seeing it in your travels please let us know about it!

Below all the recent storm snow there is a thin rain crust from the warm, wet storm on Feb 01. This rain crust has been reported to exist up to treeline elevations around 1700 m. No recent activity involving this crust has been reported.

Deep in the mid-pack there may still be a layer of surface hoar buried in late December. It's gaining strength, but should remain a concern since snowpack tests still demonstrate this layer has the potential to slide, albeit in isolated areas and/or with very large triggers.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Cornices become weak with daytime heating or solar exposure.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2.5

50 to 120 cm of storm snow fell between Wednesday Feb 12 and Monday Feb 17. The storm snow is reportedly settling nicely with time and continued cold temperatures on it's side. These conditions have also allowed for the riding quality to be ridiculously good, especially in wind sheltered mid and low elevation terrain. But at upper elevations it's a bit of a different story, fresh wind slabs likely continue to form at and above treeline.

Aspects:

North, North East, East, South East, South, North West.

Elevations:

Alpine, Treeline.

Cornices

An icon showing Cornices

Likelihood

Possible

Expected Size

2 - 3

Enormous cornices have grown on most ridge lines and natural cornice failures have been observed in the last week suggesting that many cornices hang on the brink of failure. Brief periods of the strenthening February sun could exacerbate this problem.

Aspects:

North, North East, East, South East, South.

Elevations:

Alpine.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Unlikely

Expected Size

2.5 - 3.5

An aging layer of buried surface hoar that was buried in mid-December may be found in parts of the region. There is uncertainty on where this layer is a problem and it hasn't been particularily reactive for some time. It appears to be of highest concern in sheltered terrain features near treeline.

Aspects:

All aspects.

Elevations:

Treeline.

Valid until: Feb 21st, 2020 5:00PM