Avalanche Forecast

Issued: Mar 23rd, 2016 9:02AM

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

jlammers, Avalanche Canada

Northwest Coastal.

Forecast snowfall amounts are uncertain for Wednesday night and Thursday. If more than 10cm falls, the avalanche danger may be higher than posted.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Generally light snowfall (5-10cm) is expected on Thursday. A dry ridge should develop on Friday bringing mainly clear skies while overcast conditions are forecast for Saturday. Ridgetop winds should be moderate from the southwest on Thursday and then become light for Friday and Saturday. Daytime freezing levels are forecast to hover between 1100 and 1200m for the forecast period.

Avalanche Summary

In the north of the region near Stewart, a few persistent and deep persistent slab avalanches to size 2.5 were reported on Tuesday. The avalanches were triggered by solar radiation or by large cornices falls. One of the avalanches (which was triggered by a cornice fall) occurred on a northwest aspect at about 1400m and is thought to have failed on the March 3rd surface hoar. The slab was 50cm deep, 40m wide and 80m long. New wind slab activity is expected on Thursday in response to new snow and strong winds.

Snowpack Summary

As of Wednesday morning, up to 5cm of new snow had fallen with moderate to strong southerly winds. At treeline and in the alpine small wind slabs are expected to have formed. These wind slabs overlie a variety of surfaces which include a hard crust on solar aspects above 1300, moist or refrozen snow on all aspects below 1300, and settled wind slabs in exposed high elevation terrain. A layer of surface hoar or melt-freeze crust buried on March 3 is down 50-80cm and has been on the radar of professionals in the mountains north of Stewart. A more widespread crust/facet layer buried in early February can now be found down over a metre. Both of these deeper layers have become less likely to trigger, but have the potential for large avalanches especially with a large trigger such as a cornice fall. I'd be increasingly cautious during periods of warming or solar radiation.

Problems

Wind Slabs

Continued light snowfall and strong southwest wind are forecast to form new wind slabs at treeline and in the alpine. Wind slabs may be particularly reactive due to underlying hard surfaces.

Be cautious as you transition into wind affected terrain. >Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Some cornices are the size of a bus, and will continue to grow with forecast snow and wind. Cornice collapses in the region continue to trigger large avalanches on the slope below.

Extra caution needed around cornices with current conditions.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 5

Persistent Slabs

A few persistent weaknesses exist in the mid snowpack (see snowpack description). These potentially destructive layers may become reactive with spring warming or with a large trigger such as a cornice fall.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >Conditions have improved, but be mindful that persistent instabilities are still present.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 24th, 2016 2:00PM