Avalanche Forecast

Issued: Mar 28th, 2016 8:46AM

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

rbuhler, Avalanche Canada

Sea To Sky.

Substantial warming and sun exposure on Tuesday will destabilize the upper snowpack. Extra caution is required around and below cornices, in recently wind loaded areas, and on steep sun exposed slopes.

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 as high as 3000m on Tuesday afternoon and should be above 3000m on both Wednesday and Thursday afternoon, with cooling during the overnight periods. Strong outflow winds are expected on Tuesday in exposed terrain. Light to moderate outflow winds are forecast for Wednesday and Thursday is forecast to be calm.

Avalanche Summary

On Sunday, a natural size 1 storm slab was reported from a north aspect 40 degree slope at 2000m elevation. Skiers were triggering size 1 soft slabs in wind loaded northeast aspect slopes at 1900-2000m. Explosives triggered storm slabs up to size 2. On Saturday, a natural cornice failure triggered a size 2 storm slab on a northeast aspect at 2000m. Another natural cornice failure triggered a size 2.5 storm slab on a northwest aspect at 2100m. Explosives also triggered several size 2 cornice releases. One of these cornice releases triggered a 15-40cm thick storm slab on the slope below. Loose wet sluffing was also reported on steep south facing slopes. As things heat up on Tuesday, natural cornice releases and solar triggered sluffing are both expected. Cornices have the potential to trigger lingering storm slabs on the slopes below, especially on north aspects. Wet slabs may be possible on steep south facing terrain.

Snowpack Summary

Up to 15cm of new snow accumulated over the weekend in sheltered areas. Over the weekend, southerly winds were loading north aspect leeward slopes. However, outflow winds on Monday are reported to be loading south aspects in the alpine while exposed north aspect slopes are being wind pressed and scoured. Large cornices are lingering and are expected to become very weak this week. Below the surface problems, the mid snowpack is generally well-settled throughout with no notable persistent weaknesses. On Monday, a sun crust is expected to have formed on south aspects. Melt-freeze conditions are expected to be widespread this week with very high freezing levels.

Problems

Cornices

Large cornices are expected to get weak with warming and sun exposure, and natural cornice releases are possible in the afternoon. They can be destructive by themselves, and may also become the trigger for a 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, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Wind Slabs

Wind slabs should be expected in immediate leeward features on all aspects in exposed terrain. Wind loading was from the south over the weekend but switched to north on Monday causing reverse loading.

Avoid travelling in areas that have been reverse loaded by winds. >Stay off recent wind loaded areas until the slope has had a chance to stabilize. >Be cautious as you transition into wind affected terrain. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

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.

Start and finish early before the surface crusts melt. >Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

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