Avalanche Forecast

Issued: Mar 3rd, 2012 10:04AM

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

ghelgeson, Avalanche Canada

South Rockies.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Monday

Weather Forecast

Mild temperatures and strong ridgetop winds persist through the forecast period. SUN: Cloudy with sunny breaks. FZLVL tops out near 1900m in the afternoon. Trace to 5 cm of snow expected. Ridgetop winds Strong to Extreme NW. Moderate Chinook. MON: A fast moving cold front crosses over the region, the timing of which is a bit hard to pin down. The current best guess is late in the day Monday. Regardless, freezing levels will fall with the passage of the cold front & 5 - 10 cm of snow is expected. Winds should increase with frontal passage, we can expect strong winds out of the W, switching to NW in the evening. Tue: A ridge of high pressure slides into the region bringing more seasonal cool temperatures, high solar & light winds.

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

Strong winds and have formed wind slabs up to 20 cm deep in wind exposed terrain at and above treeline as of Saturday afternoon. 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. This weekend the upper snowpack is changing character as strong to extreme winds at ridge top & mild temperatures form the old storm snow into a more cohesive slab. 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

Persistently weak buried surface hoar demands continued diligence and conservative decisions. The potential for remote triggering, step down avalanches, and wide propagations, makes this weakness particularly tricky to predict.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 6

Wind Slabs

Generally lurking below ridgecrests, behind terrain breaks, and in gullies. Fresh wind slabs are expected to be touchy and continued strong winds over the forecast period may overload weaknesses.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Cornices

Freezing levels climb to ridgetop this weekend which will loosen up the large cornices that have formed on many ridge crests. Large cornice falls have the potential to trigger deep slab avalanches.

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Mar 4th, 2012 8:00AM