Avalanche Forecast
Issued: Apr 17th, 2019 4:41PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Storm Slabs.
cgarritty,
Avalanche Canada
First warm, then rain. A one-two punch over the coming few days is expected to maintain active loose wet avalanche conditions while bringing a test to any slabs that haven't quite bonded to the crust.
Summary
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Wednesday night: Mainly clear. Moderate to strong west winds. Freezing levels rising to 2500 metres.
Thursday: Mainly sunny with cloud increasing over the day and rain showers overnight. Moderate to strong southwest winds increasing over the day. Alpine high temperatures around +6 with freezing levels rising to 3000 metres, remaining elevated overnight.
Friday: Cloudy with light rain, increasing and transitioning to alpine snow overnight. Strong southwest winds. Alpine high temperatures around +5 with freezing levels dropping to 2500 metres over the day.
Saturday: Mainly cloudy with easing wet flurries bringing up to 10 cm of wet new snow to the alpine, including overnight accumulations. Light variable winds. Alpine high temperatures around 0 with freezing levels to 2000 metres.
Avalanche Summary
An observation from the Waterton Park area describes a very large (size 3) deep persistent slab having released with a cornice trigger at some time in the past week. This occurred on a wind loaded high (2500m) north aspect on Mt. Blackiston and initiated as a wind slab before 'stepping down' to weak faceted snow in the basal snowpack. This should be treated as a reminder of the potential for weak basal snowpack conditions persisting in high alpine terrain.
The following activity resulting from the recent storm occurred in the neighbouring Lizard Range:
On Sunday storm slabs were quite sensitive to human triggering to size 2 on north through east facing slopes in the alpine and down into treeline. A little further down into treeline the snowpack was well bonded to the old crust, check out this MIN report for more details.
A natural avalanche cycle occurred Saturday night, the highlights were storm slabs up to size 2 on northeast facing alpine terrain around 1700 m. A natural cornice failure was observed from a north facing ridgeline which subsequently triggered a size 2.5 storm slab involving the new snow. We received a great MIN report of a small storm slab from Saturday morning.
Snowpack Summary
New sun and temperature crusts are likely to be found on the surface on solar aspects and below the alpine, having formed above the 10 to 20 cm of dense snow from the past weekend's storm. A similar crust interface exists between this recent storm snow and another 10-20 cm from last week. The bond of recent snow to this interface remains in question under the upcoming warming pattern. However, the underlying, older storm snow is expected to be well bonded to a widespread supportive crust found beneath it.
North facing alpine terrain may still hold a cold, dry, snowpack and also harbours a deeply buried layer of facets. Although unlikely, human triggering of persistent slabs on this layer may still be possible in rocky alpine terrain with a shallow or variable depth snowpack.
Below treeline the snowpack has melted or is isothermal.
Problems
Loose Wet
Sunny breaks and steadily rising temperatures are expected to maintain potential for loose wet avalanche activity. The likelihood of loose avalanches increases as temperatures warm throughout the day and while sun exposure is strong.
- Areas sheltered from wind but exposed to sun will be the most prone to loose wet activity.
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
- A moist/wet snow surface, pinwheeling and natural avalanches all indicate a weakening snowpack.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
10-20 cm of storm snow rests on a widespread crust. The bond at this crust is likely strengthening, but it remains in question. Meanwhile, wind loaded slabs on high north aspects will see their first punch of heat on Thursday.
- Wet slab releases may occur if poorly bonded slabs become moist with sun exposure and warming.
- Look for signs of instability like whumphing, shooting cracks, and recent avalanches.
- Avoid recently wind loaded features near ridge crests, roll-overs and in steep terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 18th, 2019 2:00PM
