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Avalanche Forecast

Archived

Mar 5th, 2012–Mar 7th, 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 avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Rockies.

Confidence

Fair - Due to limited field observations

Weather Forecast

The South Rockies should see 10 -15 cm during the day Monday and another 10 cm Monday night. Tuesday starts out cloudy & cold accompanied by light N/NE winds, there may be the occasional sunny break in the afternoon. The freezing level should stay near the surface Tuesday. On Wednesday warm air floods the region, as a result freezing levels climb to 1700m. Winds should be moderate out of the W at treeline Wednesday, Strong out of the NW at ridgetop. Thursday looks to be the warmest day with the freezing level climbing to 2500m in the afternoon. The models currently show a 3000m freezing level on Friday.

Avalanche Summary

Our field team remoted a size 2 avalanche from the flats Wednesday. It's worth checking out the details of the incident report linked to this forecast as it illustrates just how tender the persistent slab problem is in the So. Rockies. On Saturday a group of sledders remote triggered a size 1.5 avalanche which failed on the Feb.09 SH in the Coal Creek area on a North facing, 37 degree slope at 1600m.

Snowpack Summary

10cm of new snow fell during the day Monday & another 10 cm is expected Monday night along with strong NW winds. The Feb. 09 surface hoar is now down between 40 & 90 cm. The depth varies throughout the region. This weak layer continue to perform, our head field technician was out for a ski and noticed a remote triggered avalanche on Saturday. See the details below. Snowpack tests continue to show sudden moderate failures on this interface. The weekends strong winds and mild temperatures formed the upper snowpack into a more cohesive slab. Our field team will be out Tuesday so we should have a better handle on the upper snowpack later in the week. Lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones.Our field team was out in the Crowsnest Thursday where they observed a much stronger snowpack. The So. Rockies forecast is intended to give trends for the region as a whole, and as such, conditions will vary between the different sub regions.

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.

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.

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.