Avalanche Forecast

Issued: Apr 16th, 2018 4:36PM

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

jmcbride, Avalanche Canada

Purcells.

More snow Monday night will add to the storm slabs at upper elevations. These may become more reactive as the day warms or if the sun appears on Tuesday. Also watch for loose, wet activity on sunny and lower elevation slopes.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Mostly cloudy, flurries. Accumulation 10-15 cm. Ridge wind moderate to strong, southwest. Alpine temperature near -5. Freezing level 1000 m.TUESDAY: Mostly cloudy, light flurries. Accumulation up to 3 cm. Ridge wind moderate to strong, west. Alpine temperature near -6. Freezing level 1700 m.WEDNESDAY: Mix of sun and cloud. Ridge wind light, southeast. Alpine temperature near -4. Freezing level 1800 m.THURSDAY: Increasing cloud. Ridge wind light, southwest. Alpine temperature near -1. Freezing level 2200 m.

Avalanche Summary

Sunday there was a report of a near miss for skiers who triggered a size 2 wind slab on a north aspect at treeline in the northern part of the region. While in the northwestern part of the region saw a warming-induced, natural avalanche cycle up to size 3 on large alpine features in the recent storm snow.Saturday, explosive control work in northern parts of the region produced several storm slab releases size 2-2.5 on predominantly treeline to alpine, west aspects with wide propagations up to 200 m. And ski cuts produced size 1-1.5 results on cross-loaded features.Friday several skier-triggered, size 1.5 wind slab releases were reported on north aspects at 2300 m. As well as a few solar-triggered storm slab releases (size 1.5) on steep, unsupported. west-facing features at 2200 m.Wednesday there was a report of an icefall-triggered size 1.5 wind slab (50 cm deep and 50 m wide) on a north aspect at 2400 m.

Snowpack Summary

About 20 cm on new snow overlies a crust on all aspects to at least 2000 m (and possibly higher on south-facing slopes), while 30-40 cm can be found at higher elevations (and up to 60 cm in some areas in the northwest of the region). Below 2200 m this new snow has thin surface crust, breaking down to moist or wet snow in the afternoons.Within the upper snowpack there a now several buried crusts with only the mostly recently buried posing a concern with the recent storm snow..There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 50 to 90 cm below the surface. This buried crust/surface hoar interface is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or cornice collapse)Deeper persistent weak layers from December and January are considered dormant at this time.

Problems

Storm Slabs

Snow and wind Sunday night and Monday will likely form touchy storm slabs in the alpine and at treeline.

Use caution on leeward and cross-loaded terrain near ridge crests.Choose well supported terrain without convexities.Be cautious of sluffing in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Loose Wet

Warming temperatures or bit of sun may destabilize surface snow and initiate loose wet avalanche activity, especially on steep south facing features. The likelihood of cornice failures also increases with sun and warming.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Cornices become weak with daytime heating, give them a wide berth when traveling above or below.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Apr 17th, 2018 2:00PM