Avalanche Forecast

Archived

Mar 10th, 2012–Mar 11th, 2012

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Regions

Kootenay Boundary.

Confidence

Fair - Timing of incoming weather is uncertain on Monday

Weather Forecast

Saturday Night: I expect light snowfall above 1300m Saturday night with freezing levels dropping down to about 1400 m by Sunday morning. Ridge top winds should be strong overnight, with very little wind below treeline. Sunday: Freezing levels stick around 1500m for most of the day, dropping to the surface with the passage of the cold front Sunday night. I expect 10 - 20 cm of snow during the day Sunday above 1300m. Winds remain strong & steady out of the SW at ridge top. Monday morning offers brief respite from the precip and warmth. Freezing levels creep up to 1500m after lunch Monday ahead of a pacific bomb which is forecast to bring 20 -40 cm in combination with extreme SW winds beginning Monday evening, continuing through Tuesday afternoon.

Avalanche Summary

No activity to report from Friday. I've left the observations from Thursday below to shine some light on the sometimes spooky nature of the buried surface hoar problem:From Friday:Several natural avalanches were reported Thursday to size 3. One noteworthy event was a size 2 avalanche that was triggered by cornice fall. The size 2 ran 50m before triggering a size 3 avalanche in lower angle terrain. The crown was reported to be 200cm in depth, failing on the Feb. 08 SH. One reported avalanche was remote triggered from 20m away on a 35 degree slope.

Snowpack Summary

Field reports indicate that a few wet cm's of snow fell Friday night landing on surface hoar, 2-6mm on north aspects and a 2cm sun crust on solar aspects. Moist snow was found Friday to 1800m, I suspect there was little change Saturday. The leap year SH is now down around 40 - 50 cm and is failing as a resistant planar shear in snowpack tests. The early February surface hoar is down 80 - 140cm, snowpack tests show moderate to hard forces generating sudden planar shears on this layer.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.