Northwest Coastal Avalanche Forecast

Issued: Mar 8th, 2020 5:00PM

Mon Mar 9th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Low
Tue Mar 10th 2 Day Outlook
Alpine High Treeline Considerable Below Treeline Considerable
Wed Mar 11th 3 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Considerable

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

Don't let the amazing riding lure you out into bigger terrain features, we've got an active persistent slab problem in play. Watch for the formation of fresh wind slabs in exposed terrain Monday, strong southwest wind is expected.

Summary

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

The storms just keep coming.

SUNDAY NIGHT: Freezing level at valley bottom, moderate southwest wind, 2 to 4 cm of snow.

MONDAY: Overcast, freezing level rising to about 800 m, strong southwest wind, 5 to 10 cm of new snow during the day, 15 to 25 cm Monday Night.

TUESDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 10 to 20 cm of snow during the day, 5 to 10 cm Tuesday Night.

WEDNESDAY: Broken cloud cover, freezing level around 600 m, moderate west/northwest wind, 1 to 5 cm of snow possible.

Avalanche Summary

A parade of storms over the past week produced continuous natural avalanche cycles. Recent avalanches have failed on a mix of storm interfaces and persistent weak layers. Natural avalanche activity has now begun to ease off, however human triggering remains a serious concern.

On Saturday the strong March sun induced loose wet avalanches to size 2 on solar aspects at all elevations. Small shallow soft slabs were running in the new snow producing avalanches to size 1. A few natural wind slabs to size 2 were reported from north facing alpine features too. Good visibility allowed for more observations of very large avalanches that ran during and just after the last storm, big terrain features produced avalanches up to size 3.5.

Improved visibility on Friday allowed for more observations of recent avalanches, which included size 1.5 to 2.5 persistent slabs failing on our March 1st surface hoar layer and storm slabs as well as a size 3 (very large) glide slab. No new avalanches were noted during the day, indicating that conditions had transitioned from a natural cycle toward likely human triggering.

Several more size 1 to 2 (small and large) persistent slab avalanches were triggered with skier traffic in the Stewart area on Thursday, noted for releasing in remarkably low angle terrain. Weather limited observations in the Terrace area, although one new size 2.5 storm slab was observed failing on a reloaded slope and increasing the debris in its runout zone. 

Glide cracks continue to open and glide slabs are releasing, resulting in size 2 to 3 avalanches almost every day.

Snowpack Summary

15-25 cm of new snow over Thursday brought snow totals from the first week of March to 100 cm or more. Each round of snowfall has been accompanied by strong south winds, leaving us with wind slabs in leeward terrain and two layers of surface hoar from February that are now deeply buried.

The first of these layers was buried on March 1st and is currently 50-100 cm below the surface, the other was buried on February 19th and is closer to 90-140 cm below the surface, with the greatest depths found at higher elevations. On solar aspects (south through west) this surface hoar may be resting on a buried crust which may continue to act as a sliding surface for overlying slabs. Reduced accumulations of recent snow overlie a rain crust below about 1000 m. The most suspect slopes can be found at treeline elevations and at the higher end of below treeline where preserved surface hoar most likely exists.

A layer of weak and sugary faceted grains that formed in January may be found about 130 to 180 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers have produced a few very large natural and explosive triggered avalanches over the past two weeks.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Be alert to conditions that change throughout the day.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2.5

Large, dangerous wind slabs have formed as a result of recent snowfall and strong winds. Newly formed wind slabs combined with deeply buried persistent weak layers makes the consequence of triggering any avalanche high.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3

Two surface hoar layers are found 50-100 cm and 90-140 cm below the surface. These layers produced large natural and human triggered avalanches as recently as Friday. They are most problematic at shaded treeline elevations where the surface hoar is well preserved. 

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Mar 9th, 2020 5:00PM