Avalanche Forecast
Issued: Feb 23rd, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
ghelgeson,
Avalanche Canada
This is a rather unusual situation where storm slabs may actually be most sensitive to triggering at lower elevations because the new snow rests on a touchy layer of buried surface hoar. Stick to simple, mellow, well supported terrain and avoid convexities and terrain traps.
Summary
Confidence
Low - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
A few light systems look to be with us for the first half of the week ahead of some heavy hitters that begin to impact the region Wednesday, then it’s one big storm after the next through the weekend.
SUNDAY NIGHT: Freezing level around 800 m, moderate northwest wind, 2 to 6 cm of snow.
MONDAY: Scattered cloud at dawn building to overcast by sundown, freezing level around valley bottom, light west/northwest wind, no significant precipitation expected.
TUESDAY: Overcast, freezing around 700 m, strong southwest wind, 5 to 10 cm of snow during the day, with another 5 to 15 cm expected Tuesday Night.
WEDNESDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 5 to 20 cm of snow.
Avalanche Summary
On Saturday natural slab avalanches ran on the February 19th surface hoar producing avalanches to size 2 on north and northeast facing aspects at 1200 m. Storm slabs running on the surface hoar were sensitive to skier triggering between 1300 and 800 m, this is worth highlighting as these elevations are at and below treeline. Small loose dry avalanches were also reported in the Shames backcountry in this MIN report.
A widespread natural storm slab cycle up to size 2.5 occurred during the storm Thursday night and Friday. Skier accidental and remote triggered storm slabs were reported up to size 1.5, releasing on the underlying surface hoar. The slabs were 30 to 50 cm deep and on north to east aspects.
Snowpack Summary
40 to 70 cm of new snow has formed storm slabs at all elevations. The slabs are likely deepest in lee alpine terrain features, as the snow fell with strong south to west wind.
These slabs may slide easily where they overly a couple layers of surface hoar that may be found in sheltered terrain at and below treeline or a melt-freeze crust on sun-exposed aspects. You may find these layers around 50 and 80 cm deep.
A thin layer of weak and sugary faceted grains that formed in January may be found about 120 to 170 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers produced a few large natural avalanches in early-February but have recently been unreactive.
Terrain and Travel
- Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
- The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
- Be especially cautious as you transition into wind affected terrain.
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
Problems
Storm Slabs
Storm slabs are a serious problem at all elevations and may actually be the most sensitive at lower elevations. At and below treeline up to 60 cm of snow rests on well-preserved surface hoar. The alpine is a bit of a different story, there the storm snow has been heavily affected by wind and slabs are 30 to 90 cm in depth. Storm slabs may rest on a melt-freeze crust on sun-exposed aspects too. The deepest deposits will likely be in lee terrain features near ridges, as the snow fell with strong south to west wind.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 24th, 2020 5:00PM
