Avalanche Forecast

Issued: Mar 29th, 2016 9:27AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Deep Persistent Slabs, Cornices and Loose Wet.

rbuhler, Avalanche Canada

Northwest Inland.

A special warning has been issued for the substantial warming and sun this week. Deeply buried weaknesses within the snowpack are expected to wake-up and produce very large avalanches. It is best to avoid avalanche terrain during the heat of the day.

Summary

Confidence

Moderate

Weather Forecast

A ridge of high pressure dominates for the rest of the week. Sunny and dry conditions are expected for Wednesday through Friday. Freezing levels are expected to be above 3000m each afternoon, with cooling overnight. Light to moderate outflow winds are expected in the alpine for the forecast period.

Avalanche Summary

No new avalanches were reported on Monday. On Sunday, a natural icefall entrained surface snow and was reported as size 2. Isolated natural wind slabs were reported to size 1 on east aspects at treeline. In the far north, natural cornice releases were reported to have triggered slabs up to size 3.5 which were stepping down to ground. Point releases were reported up to size 2 and glide cracks up to size 2.5. On Wednesday, continued warming and sun exposure are expected to result in natural cornice releases and may also result in deep persistent slab releases. A weak basal layer means avalanches may step down to the ground. Loose wet sluffing is expected from steep sun exposed slopes.

Snowpack Summary

At treeline and above small wind slabs overly a variety of surfaces include crust on solar aspects above 1300 m, moist or refrozen snow on all aspects below 1300 m, and settled wind slabs in exposed high elevation terrain. Surface hoar from March 23rd is still being mentioned in the northern half of the region, and now may be covered by up to 20cm of recent storm snow. Professional operators are tracking two deep weak layers from early-January and February that are now down about 1 meter or more. These layers are generally dormant but might wake up with increased warming or a heavy trigger (like a cornice fall). Basal facets exist in some areas and have been shown to be reactive in the north of the region. Rapid warming may wake up deeply buried weak layers.

Problems

Deep Persistent Slabs

Deeply buried weak layers which have been dormant recently are expected to wake up this week with the substantial warming and sun exposure. Very large avalanches are expected this week.

Cornice releases have the potential to trigger deeply buried weak layers. >Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Be aware of the potential for full depth avalanches due to deeply buried weak layers. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Cornices

Large lingering cornices are expected to become weak with the substantial warming and sun exposure this week. They can be destructive by themselves, and may also become the trigger for a large slab avalanche on the slope below.

Give cornices a wide berth when traveling on or below ridges. >Cornices become weak with daytime heating, so travel early on exposed slopes. >Extra caution needed around cornices with current conditions. >

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Loose Wet

Loose wet sluffing is expected on sun exposed slopes during the heat of the afternoon. Rising freezing levels may increase the size and run length of natural sluffing.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Avoid travelling on ledges and cliffs where sluffing may have severe consequences. >Be cautious of sluffing in steep terrain. >

Aspects: North, North East, East, South East, South.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 30th, 2016 2:00PM