Avalanche Forecast

Issued: Mar 2nd, 2020 1:00AM

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

Bill Phipps, VIAC

Vancouver Island.

Numerous observations were reported of natural slab avalanche activity as the recent storm snow failed (Fridays storm) in the west and northern areas of the forecast region, with multiple avalanches up to size 2-2.5.

Summary

Past Weather

10 to 50 cm of new snow fell with Friday's storm. Accompanied by strong winds from the SE-SW this new snow created reactive windslabs in in the alpine and treeline elevation bands. The new snow came in warm and luckily had a half decent bond to old surfaces. Things calmed down Saturday through Sunday with light new snowfall and winds. Clear skies and warmer temps Saturday gave the snow surface a thin sun crust on solar aspects before the light snow fell Saturday night.

Weather Forecast

Moderate snowfall and strong winds are forecast for this period. Monday- 4 to 12 mm of new precip (possibly falling as rain at low and mid elevations and snow up high). Winds moderate to strong from the SW. Temps +2 to 0. Freezing levels 2000 to 2500 m. Tuesday- 5 to 15 cm of new snow. Winds light SW rising to strong SW-SE. Temps 0 to -5. Freezing level 800 to 900 m.Wednesday- 5-10 cm of new snow. Winds moderate SW-SE. Temps -5 to -8. Freezing level 700 to 800 m.

Terrain Advice

Moderate new snowfall over the next three days will increase the load on our persistent weak layer (in our mid snowpack) and strong winds will move this new snow to lee slopes and create wind slabs. Be cautious as you enter, or even better avoid these windloaded slopes at treeline and in the alpine elevations bands.

Snowpack Summary

Well it seems winter is not done with us yet! With a decent storm Friday dumping 10 -50 cm of fresh we are still deep in ski and sled mode. More new snow falling during this forecast period in moderate pulses will add more weight to our persistent weak layer in the mid snow pack and strong winds will create and add to wind slabs on lee slopes.

Snowpack Details

Surface: a few cms of new snow falling on a thin sun crust on solars and on old snow on non solars
Upper: Fridays storm snow 10-50 cm falling on older storm snow (20 to 50 cm) with a few thin crusts
Mid: a thick crust with weak snow crystals on top and some weak crystals forming below as the crust degrades
Lower: well settled

Confidence

High - Weather models in agreement and good field data.

Problems

Persistent Slabs

The persistent weak layer of snow crystals (surface hoar and facets) over a crust is now down 30 to 100 cm in our snowpack. This layer is slowly becoming less likely to react as it settles, but more new snow will increase the potential size of avalanche it could produce. This weakness is found on NE-NW aspects at treeline and is possible to unlikely to trigger with human and natural activities and could produce up to size 3 avalanches.

Likelihood

Possible

Expected Size

1 - 1

Storm Slabs

Fridays storm snow plus more moderate snowfall over the next three days will result in beefing up already existing and creating new storm slabs. Strong winds will mean that most of these slabs will be located on lee slopes (NW-NE) at treeline and alpine elevation bands. These slabs will likely produce avalanches with human activity and may possibly trigger naturally up to size 2.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Mar 3rd, 2020 1:00AM