Avalanche Forecast

Issued: Apr 20th, 2013 10:27AM

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

swerner, Avalanche Canada

South Columbia.

The Public Avalanche Forecasts and Danger Ratings will come to an end on Tuesday. General spring messaging will be found under the Forecast Details tab below.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

The Interior will remain under a cool, dry North-West flow through Tuesday. A slow warming trend will persist through the end of next week.Sunday: Scattered-broken cloud cover, allowing some sunshine through. Â Ridgetop winds will blow light from the North. Freezing levels 1400 m and falling to valley bottom overnight.Monday/Tuesday: Mostly clear, sunny skies. Ridgetop winds will blow light from the NW. Freezing levels 1700 m in the afternoon and falling to 1000 m overnight.

Avalanche Summary

On Friday, reports of the new storm snow was sluffing from steep terrain up to size 2.Â

Snowpack Summary

At higher elevations up to 25 cm of new snow sits on a series of melt-freeze crusts (solar aspects) and some smaller surface hoar crystals (northerly aspects). Touchy wind slabs exist on lee slopes and behind terrain features and cornices are huge, threatening slopes below.Deeper in the snowpack (60-120 cm down) a weaker interface exists comprising of crusts, and surface hoar. Earlier this week, very large avalanches were reactive on this interface in the neighboring Glacier National Park. I would practice caution and remain suspicious of steeper, high alpine slopes.

Problems

Wind Slabs

Wind slab problems exist on lee slopes and behind terrain features at treeline and above. Large looming cornices exist on ridgelines and pose a threat to slopes below. Keep well back and watch your overhead hazards.

Use ridges or ribs to avoid pockets of wind loaded snow.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

On Monday, an interface buried down about 60-120 cm created surprisingly large avalanches in neighboring regions. Smaller avalanches, cornice fall or the weight of a person hitting a thin-spot, may trigger a large avalanche & destructive avalanche.

Be aware of thin areas that may propagate to deeper instabilites.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 6

Valid until: Apr 21st, 2013 2:00PM