Avalanche Forecast
Issued: Mar 4th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
An intense storm will impact the region over the day on Thursday. Storm slabs will build over the day and will likely become touchy once enough snow accumulates. The snow will also load a buried weak layer. Treat the danger as HIGH if you find 30+ cm of accumulation.
Summary
Confidence
Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.
Weather Forecast
WEDNESDAY NIGHT: Increasing cloud with early-morning snowfall, accumulation 5 cm, light increasing to strong southwest wind, treeline temperature -3 C, freezing level 800 m.
THURSDAY: Cloudy with snowfall, accumulation 15 to 25 cm and the most in the north of the region, strong southwest wind, treeline temperature -1 C, freezing level 1000 m.
FRIDAY: Early-morning snowfall then a mix of sun and cloud, accumulation 5 to 10 cm, light southwest wind, treeline temperature -4 C, freezing level 700 m.
SATURDAY: Cloudy with snowfall, accumulation 10 to 15 cm, light south wind, treeline temperature -5 C, freezing level 600 m.
Avalanche Summary
A few small (size 1) wet loose avalanches were observed in the North Shore mountains on Tuesday.
Avalanche activity is expected to spike on Thursday during the stormy weather.
Snowpack Summary
The next storm on Wednesday night into Thursday will drop around 20 to 30 cm of snow, with the most expected in the north of the region. The snow will likely consolidate into a storm slab as the day unfolds, with particularly touchy conditions during periods of rapid snow loading. The wind will be strong from the southwest during the storm, so expect wind slab development in lee terrain features, particularly near ridges.
In some of the region, around 50 to 80 cm of snow overlies a layer of surface hoar on north-facing aspects near and above treeline. The layer has been found to be reactive snowpack tests, such as in this MIN and this MIN. This persistent weak layer warrants investigation and a conservative terrain use strategy. Check out the latest forecaster blog that offers a deeper dive into these conditions.
The remainder of the snowpack is well-settled. The snowpack depth varies from around 250 to 300 cm at the peaks of the North Shore mountains (1400 m), tapering rapidly with elevation.Â
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Dial back your terrain choices if you are seeing more than 20 cm of new snow.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Surface hoar distribution is highly variable. Avoid generalizing your observations.
Problems
Storm Slabs
Around 20 to 30 cm of snow is forecast to accumulate across the region on Thursday. Storm slabs will grow over the day and become touchy during periods of rapid loading from snowfall and/or strong wind. The snow will fall with strong southwest wind, so the deepest deposits will be in lee terrain features. Use added caution if you find more than 20 cm of snow accumulate from the storm.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A weak layer of feathery surface hoar may be found around 50 to 80 cm deep on northerly aspects around treeline and lower alpine elevations. A persistent slab problem is not typical for the region and there is high uncertainty with regard to how quickly it will stabilize. Assess the layer in the snowpack prior to entering committing avalanche terrain or adopt a conservative mindset to avoid the problem.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 5th, 2020 5:00PM
