Northwest Coastal Avalanche Forecast

Issued: Mar 18th, 2021 4:00PM

Fri Mar 19th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Moderate
Sat Mar 20th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low
Sun Mar 21st 3 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Moderate

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

The current storm is light duty compared to what the region has seen recently, but fresh wind slab hazards should still figure into your travel decisions. Deeper recent storm interfaces and more stubborn older wind slabs shouldn't be ruled out quite yet.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Thursday night: Cloudy with continuing flurries bringing about 5 more cm of new snow. Moderate to strong southwest winds.

Friday: Cloudy with continuing scattered flurries bringing up to 5 more cm of new snow. Moderate to strong southwest winds. Alpine high temperatures around -7.

Saturday: Cloudy with a stronger storm pulse starting with a trace to 5 cm of new snow then increasing quite a bit overnight. Moderate to strong south winds becoming extreme overnight. Alpine high temperatures around -7.

Sunday: Cloudy with continuing flurries bringing an uncertain 5-15 cm of new snow, closer to 10-30 cm with overnight accumulations. Extreme south winds easing to light southwest by evening.

Avalanche Summary

A natural wind slab avalanche cycle with numerous wind slabs from size 2 to 3.5 (large to very large) was reportedly ongoing in the Bear Pass area on Wednesday morning. No other new avalanche activity has been reported, but stormy weather has been limiting observations and conditions in some other parts of the region over the past couple of days may well have mirrored those noted in the Pass. Natural wet loose and glide avalanches accompanied this activity below about 900 metres.

Explosive control work on Monday produced storm slab avalanches up to size 2. 

A widespread natural avalanche cycle with storm slab avalanches up to size 4 (VERY LARGE!) occurred through last weekend. Most natural avalanche activity were observed on solar aspects within the storm snow. On shaded aspects, avalanches may have run on a layer of surface hoar which formed prior to the arrival of the storm.

Snowpack Summary

5-10 cm per 12 hour period is expected to accumulate over the next couple of days. Combined with forecast winds, the new snow is expected to form fresh slabs in lee features at treeline and above on an ongoing basis. It will otherwise add to 10-15 cm of new snow already atop last weekend's storm totals ranging from 50 cm in the north to 150 cm in the south of the region. Rain fell below 900 m over the weekend, saturating the upper snowpack at lower elevations.

Collectively, the new snow and recent storm snow may overlie a persistent weak layer of surface hoar buried March 12 on sheltered northerly aspects around treeline or a melt-freeze crust on southerly aspects and below treeline.

Around 100 to 300 cm now overlies a persistent weak layer buried in mid-February that may still be a concern in isolated parts of the region. The layer consists of surface hoar in areas sheltered from the wind and facets that formed during February's cold snap. 

Conditions are lending themselves to these persistent layers stabilizing, but professionals in the region are continuing to track and treat them with caution, especially the shallower layer from March.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Choose conservative terrain and watch for clues of instability.
  • Make observations and assess conditions continually as you travel.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2.5

A bit more snow and a lot more wind is likely to continue forming fresh wind slabs over more stubborn older slabs on Friday. Although wind slabs are the main issue, keep your guard up in steep sheltered terrain. Recent accumulations may be sitting on a weak layer of surface hoar on north aspects or a crust on solar aspects and lower elevations.

Aspects:

North, North East, East, North West.

Elevations:

All elevations.

Valid until: Mar 19th, 2021 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.