Avalanche Forecast

Issued: Mar 28th, 2016 9:47AM

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 Wind Slabs.

rbuhler, Avalanche Canada

Northwest Inland.

Substantial warming and sun exposure this week are expected to wake-up deeply buried weaknesses within the snowpack. Conservative terrain selection is critical and it is best to avoid avalanche terrain during the heat of the day.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A blocking ridge of high pressure is the dominant feature for the week. Dry and clear conditions are expected for Tuesday through Thursday. Freezing levels are expected to climb to around 2700m on Tuesday afternoon and should be above 3000m on both Wednesday and Thursday afternoon, with cooling during the overnight periods. Strong northwest winds are expected on Tuesday in exposed terrain. Light to moderate northwesterly winds are forecast for Wednesday and light northwesterly winds for Thursday.

Avalanche Summary

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 Tuesday, substantial warming and sun are expected to result in natural cornice releases and may also result in deep persistent slab releases. Lingering wind slabs also remain a concern.

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.

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

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

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Recently strong southerly winds have loaded leeward features in exposed terrain around ridge crests.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 29th, 2016 2:00PM