Avalanche Forecast

Issued: Nov 26th, 2018 5:05PM

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

ghelgeson, Avalanche Canada

Sea To Sky.

Significant snowfall accompanied by strong southerly wind is expected to produce a natural avalanche cycle above 2000 m that may persist into Tuesday. Better visibility, riding conditions and reduced avalanche danger are expected later in the week.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

An atmospheric river is expected to deliver significant precipitation, strong to extreme wind and warm temperatures to the Sea-to-Sky region through Tuesday. The overall flow should become more westerly Tuesday night allowing the freezing level to return to treeline by Wednesday. A weak ridge is anticipated for the latter half of the week with potential for another significant series of storms by the weekend.MONDAY NIGHT: Freezing level around 2000 m, strong to extreme south/southwest wind, 20 to 40 mm of precipitation (!) which will likely fall as wet heavy snow at upper elevations.TUESDAY: Overcast, freezing level beginning around 2000 m, lowering to 1700 m in the afternoon, moderate to strong southwest wind, 10 to 25 mm of precipitation expected.WEDNESDAY: Broken cloud cover, freezing level holding around 1400 m, light to moderate southwest wind, 2 to 8 mm of precipitation possible.THURSDAY: Scattered cloud cover, freezing level around 1000 m, light variable wind, no significant precipitation expected.

Avalanche Summary

On Monday natural loose wet avalanches to size 1 were reported on steep cutbanks near treeline. Loose wet avalanches to size 1 were also skier triggered. On Friday and Saturday natural and skier-triggered storm slab avalanches were observed out of steep, wind-loaded terrain at alpine elevations in the Whistler area. Please submit any observations you have to the Mountain Information Network here,

Snowpack Summary

Monday's intense precipitation event rain-soaked the existing snowpack up to 1800 m and left wet snow in place up to 2000 m. Strong to extreme wind on Monday likely created touchy storm slabs, cornices, and wind damaged snow in high elevation alpine terrain. The deepest snow is found at alpine elevations, with depths of 60 to 140 cm. See this report from Brew Lake and this report from Shovelnose Creek for an idea of recent conditions. Approximately 50 cm of moist new snow now lies above a thin rime ice lens formed over the weekend. A thicker melt freeze crust can be found 75 to 90 cm below the surface. This crust may be associated with weak faceted crystals in some places where it lies close to the ground. This is most likely to cause problems in glaciated terrain or on smoother, high elevation slopes where the summer snow did not melt out.

Problems

Storm Slabs

Touchy storm slabs are expected to continue to form at high elevations that see heavy snowfall instead of heavy rain. Strong winds will speed slab formation in the lee of wind-exposed terrain features.

Cornices are already looming large on many ridges lines. Avoid travel on or underneath them.Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.Be especially careful around wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Very Likely - Certain

Expected Size

1 - 2

Loose Wet

Heavy rain is set to saturate the snowpack at lower elevations and promote active loose wet avalanche conditions.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Use extra caution around steeper slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Very Likely - Certain

Expected Size

1 - 1.5

Valid until: Nov 27th, 2018 2:00PM