Avalanche Forecast

Issued: Mar 11th, 2014 9:38AM

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

rbuhler, Avalanche Canada

Sea To Sky.

Strong solar radiation and high freezing levels may elevate hazard and could trigger natural avalanche activity on south facing slopes during the day.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

High pressure conditions will remain for Wednesday and Thursday but a pulse of moisture may cross the region late Wednesday. A more organized system is expected for Friday and will likely result in light flurries or rain. Wx models are currently uncertain regarding precipitation amounts and timing for Friday.Wednesday: A mix of sun and cloud, scattered flurries in the evening 0-3cm, freezing level 600-800m overnight, ~2000m afternoon, ridgetop wind 15-30 km/h SWThursday: A mix of sun and cloud, freezing level 800-1200m overnight, ~1700m afternoon, ridgetop wind light SWFriday: Snow or rain 3-10mm, freezing level 1000-1200m overnight, ~2000m afternoon, ridgetop wind 15-30 km/h SW

Avalanche Summary

During the storm on the weekend, we saw widespread natural slab avalanche activity. Most of this activity involved the storm snow itself but there were numerous avalanches which stepped down to the early-March weak layer or possibly even the February weak layer. Now that the storm is over, natural activity is tapering off but large avalanches are still possible. On Monday, we received reports of slab avalanches up to size 2.5, both natural and human-triggered. At lower elevations, loose wet sluffing from steep solar aspects is being reported.

Snowpack Summary

The weekend storm produced 30-50 cm of dense snow with strong southerly ridgetop winds. Freezing levels have been cycling between valley bottom and roughly 1700m, and low elevation terrain saw significant rain on the weekend. Expect to find a crust at or near the surface below treeline. The early March melt-freeze crust is now down roughly 90-150 cm. This layer was found on all aspects at treeline and below, and on all but North aspects in the alpine. The early-Feb weak layer is down over 1.5m and is generally not a concern for human-triggering but avalanches or cornice falls have the potential to trigger it.

Problems

Storm Slabs

Weaknesses may still exist within or under the storm snow from the weekend. Old wind slabs in exposed NW through E facing terrain are being more stubborn but may still be a concern. Use increased caution during the heat of the afternoon.

Choose well supported terrain without convexities.>Avoid steep lee and cross-loaded features - typically exposed North and East facing slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Persistent Slabs

There are a couple of old weak layers buried between 100 and 200 cm deep. It has become much less likely to trigger these but storm slab avalanches or cornice falls may step down to one of these layers.

Be aware of the potential for large, deep avalanches.>Avoid thin, rocky or sparsely-treed slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Cornices

Cornices may become weak during daytime warming.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Stay well back from cornices.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Mar 12th, 2014 2:00PM