Avalanche Forecast Lizard Range and Flathead

Thursday 7th February 2019

Avalanche Danger Ratings Thu 7th Feb 5:02PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Considerable Danger Ratings Below Treeline: Moderate Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs

Avalanche Canada Forecaster: cgarritty

Date Issued:

Valid Until:

Check out the Forecasters' Blog here for insight on managing the persistent slab problem affecting the Lizard Range.A Special Public Avalanche Warning is in effect in this region.

Confidence

High -

Weather Forecast

Thursday night: Cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds.Friday: Mainly cloudy with continuing scattered flurries bringing a trace to 3 cm of new snow, continuing overnight. Alpine high temperatures around -17 and falling over the day.Saturday: Mainly cloudy with continuing isolated flurries and a trace of new snow. New snow totals of around 5-10 cm. Light northeast winds. Alpine high temperatures around -27.Sunday: Cloudy with sunny periods. Light northeast winds. Alpine high temperatures around -22.

Avalanche Summary

Another size 1.5 slab was ski cut on an east aspect at 1800 metres in the Fernie area on Wednesday. The slab was 40 cm deep and is described as a storm slab, failing at our most recent new snow interface. A 50 cm-deep size 1.5 persistent slab was triggered with a ski cut on Monday. This occurred on a north aspect at 1720 metres in the Fernie area. This is the latest of several recent observations of persistent slab avalanches failing on the persistent weak layer that was buried in mid-January. It was more widely reactive during and immediately after the storm this past weekend. The persistent weak layer producing these avalanches is described in the Snowpack Summary below.The past few days have also produced reports of wind slabs reacting to ski cutting and to explosives in the Fernie area. Sizes ranged from 1-2 and results have been focused on northeast to northwest aspects.

Snowpack Summary

Around 60 mm of precipitation fell last Friday. Above 1600 m, this produced 30-40 cm of new snow which has since been redistributed by strong winds from both north and south. It may sit on weak and feathery surface hoar crystals in shaded and sheltered areas. Below 1600 m, the precipitation fell mainly as rain and formed a new melt-freeze crust on the surface.Above 1600 metres, the mid-January layer of surface hoar and/or crust is now buried around 40 to 60 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m. The melt-freeze crust is found on south aspects at all elevations. Slabs that exist above a combination of surface hoar and crust are likely to be particularly reactive. This layer is the subject of our Special Public Avalanche Warning.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may hold weak and sugary faceted grains near the base of the snowpack.

Persistent Slabs Persistent Slabs

Likelihood

Likely - Possible

Expected Size

1.5 - 2.5

The recent storm brought a critical load to a persistent weak layer now buried 30-70 cm deep. This layer consists of surface hoar preserved in shaded, sheltered areas between 1600-2000 m. It may coexist with a crusty sliding surface on south aspects.

Increase caution around open features from 1600-2000 m, such as cutblocks, gullies, and cutbanks.Choose simple terrain and low-consequence slopes in areas where buried surface hoar may be preservedWatch for signs of instability such as whumpfing or cracking. Especially at treeline and below.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

More
Wind Slabs Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Recent snow above 1600 m has been redistributed by southwest winds that switched to northeast. Deposits in the lee of wind-exposed terrain features may remain reactive to human triggering, particularly near ridges.

If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Use caution around recently wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

More
Offline, Anywhere Members can email a forecast to themselves, meaning it's available offline Join