Avalanche Forecast

Issued: Jan 7th, 2015 8:15AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs, Loose Wet and Persistent Slabs.

rbuhler, Avalanche Canada

Northwest Coastal.

Lingering storm instabilities means conditions may remain tricky for a couple days. Rapid warming or sun may increase the likelihood of triggering a slab.

Summary

Confidence

Fair

Weather Forecast

A strong warm ridge of high pressure sits over the SW part of the region while cold Arctic air sits to the NE. On Thursday, mostly cloudy conditions with periods of sun are expected across the region with light alpine winds. Freezing levels in the south of the region may reach as high as 3000m with the warmest layer of air sitting between 1500m and 2000m (+5 deg C or warmer possible). The north of the region should remain below zero but a temperature inversion is expected. On Friday, some of the above-freezing air may reach the north of the region but the valleys should remain cold. The inversion and warm air are expected to break down on Friday night and freezing levels should be around 500m on Saturday. Winds should remain light on Friday and Saturday. 4-8mm of precipitation are forecast for Saturday.

Avalanche Summary

On Tuesday, several natural size 2 avalanches were reported in the Terrace area. On Monday, natural and explosive triggered avalanches up to size 2.5 were reported in the central part of the region. Natural avalanches activity is expected to decrease on Thursday but isolated natural avalanches are possible. The potential for human triggering remains high on Thursday.

Snowpack Summary

Storm snow amounts vary across the region. Since the weekend, southern areas received 50-80cm of new snow and the north probably around half that. Strong winds are one common theme in all areas though. Ridge winds were cranking from the SE-SW stripping windward slopes bare and probably forming hard or dense wind slabs in lee and cross-loaded areas. A buried surface hoar layer down around 70cm may be more prevalent in northern sections like Bear Pass and Ninginsaw Pass. The mid December crust can be found down around 1m and is sandwiched with facets and surface hoar. The November crust down near the bottom of the snowpack is generally well bonded but is still reactive in some test profiles. The deeper snowpack weaknesses could 'wake up' with heavy loading from new snow and wind.

Problems

Storm Slabs

Heavy snowfall and strong winds have built storm slabs in the south of the region. In the northern areas that received less snowfall, wind slabs are the primary concern.

Be cautious as you transition into wind affected terrain.>Avoid steep, open slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Loose Wet

Warm air and periods of sun may destabilize the snow surface. Sluffing is expected from steep sunny slopes and have the potential to trigger larger slab avalanches.

Be cautious of sluffing in steep terrain.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

There are a couple buried persistent weak layers in the upper and mid snowpack, primarily in northern areas like Bear Pass and Ninginsaw Pass. The weight of the new snow may increase the likelihood of triggering one of these layers.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Use caution around convexities, ridge crests, rock outcroppings and anywhere else with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Jan 8th, 2015 2:00PM