Avalanche Forecast

Issued: Dec 21st, 2013 8:55AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs and Deep Persistent Slabs.

ghelgeson, Avalanche Canada

Northwest Coastal.

An extremely conservative approach is essential Monday!

Summary

Confidence

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

Weather Forecast

Synopsis: The weather for the next 24 hours is super complex. The bottom line is that the NW coast is going to get hammered by southwesterly flow. The models suggest that the most extreme warming will be west of Terrace where the freezing level is forecast to go to 2000m Sunday. Bear Pass is forecast to see a freezing level of 900m. As a result, I'm going to issue a Wx for Kasiks and then a separate Wx that should be closer to a regional average for the rest of the NW Coastal Region.Kasiks:Sunday: Freezing Level: 2300m Precip: Snow & Rain, heavy at times 15 /25mm 30 /50cm Wind: Mod gusting Extreme, SWMonday: Freezing Level: 700m Precip: 5/10mm 10/20cm Wind: Mod gusting Strong, W Tuesday: Freezing Level: 700m Precip: 1/5mm - 2/10 cm Wind: Lht W occasionally gusting Strong.Regional Average:Sunday: Freezing Level: 700m 1000m Precip: Snow & Rain, heavy at times 15 /25mm 30 /40cm Wind: Mod gusting Extreme, SWMonday: Freezing Level: 700m Precip: Trace Wind: Strong, W Tuesday: Freezing Level: 700m Precip: Trace Wind: Lht W occasionally gusting Strong.

Avalanche Summary

On Friday the region saw a storm cycle that averaged Size 2.0 with one natural 3.0 reported from a steep start zone. Lot's of loose snow moving on Friday too.

Snowpack Summary

Total snowpack depth in the region ranges between 150 - 250cm. On December 20th Kasiks (Between Terrace & Rupert) picked up almost 50cm while Bear Pass saw around 20cm. This snow rests on a variety of old surface layers: old wind slabs, a crust that formed on Dec. 14 in some locations and even small grained surface hoar. This brings the total load of snow on the December 12 layer to 75 - 130 cm. December 12th is a surface hoar/facet combo formed during the early December cold snap which rests on old wind slabs and melt freeze crusts. Strong winds out of the South & West have been working overtime to redistribute storm snow from the past week into what is now a widespread wind slab problem at and above treeline.The mid pack is composed of various faceted layers and crusts. A significant basal facet/crust combo lingers near the base of the snowpack and is most prevalent on NW - E facing aspects at the upper TL and alpine elevations.

Problems

Storm Slabs

The big test for our dog's breakfast of a snowpack is upon us. Significant snow and rain will likely result in a large and destructive avalanche cycle. Travel only in gentle well supported terrain free of overhead hazard.

A very conservative approach is essential at this time.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 5

Deep Persistent Slabs

If we're going to see a cycle that involves the deep persistent slab failing near the ground, the time is now. The only terrain suitable for backcountry travel on Sunday is very, very gentle terrain free of overhead hazard.

Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid areas with overhead hazard.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 6

Valid until: Dec 22nd, 2013 2:00PM