Avalanche Forecast

Issued: Dec 18th, 2017 5:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs.

istorm, Avalanche Canada

Lizard-Flathead.

Tuesday's danger ratings assume the storm gets going in the morning and is cranking in the afternoon. If the storm is delayed avalanche danger could be one level lower.

Summary

Confidence

Moderate - Timing of incoming weather systems is uncertain on Tuesday

Weather Forecast

The storm track is aligned with the Canada -- USA border; the Lizard and Flathead are in the bulls eye for Tuesday's storm.The region received higher than forecast amounts overnight Sunday with the Lizard range showing around 50 cm of storm snow by mid-day Monday. Light snow may continue overnight Monday with less than 10 cm accumulating by Tuesday morning.Tuesday: Snow begins again with heavy snow forecast Tuesday afternoon. Accumulations up to 35 cm are possible. Southeast or east winds with temperatures around -10 C. Snow continues overnight with another 20 to 30 cm likely.Wednesday: Mix of sun and cloud with flurries tapering off. Cool temps in the -15 to -20 range. Light northeast wind. Storm snow accumulations from Sunday evening to Wed morning may end up in the 100 to 150 cm range.Thursday: Mix of sun and cloud, nil precipitation, light west wind, alpine temperatures around -10 to -15 C.Beyond Thursday is looks continued cold and dry ....

Avalanche Summary

Natural and explosive triggered avalanche cycle reported in the Lizard Range up to size 2.5 or 3. All aspects except west facing and all elevations from 1600 m and higher.

Snowpack Summary

Monday morning dawned with up to 50 cm of fresh snow; triple what was forecast to fall overnight! Temperatures started cold and finished warmer so the storm snow is "upside down".Prior to Sunday's storm, at or just below the surface there is a wide range of conditions. Windward slopes have been scoured down to the old rain crust and/or rock. Sun and temperatures crusts have formed on south through west facing slopes. In sheltered terrain at and below treeline, large feathery surface hoar and sugary facets exist. Roughly 30 to 60cm below the surface you should be able to find a hard crust that was buried near the end of November. This crust is approximately 30cm thick and extends from 1600m to mountain top on all aspects. Below this crust, the snowpack is moist to ground. Average snowpack depths at treeline in the region range from 70 to 110cm.

Problems

Storm Slabs

Storm snow totals of 100 or 150 cm by Wednesday. Avalanches could be large and run further than expected. It's a good time to throttle back more than you think is required and minimize exposure to overhead hazard as well as the terrain you're on.

Minimize exposure during periods of heavy loading from new snow and wind.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.Be especially cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Dec 19th, 2017 2:00PM