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Avalanche Forecast

Archived

Nov 27th, 2018–Nov 28th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

As rain turns to snow in the alpine Tuesday night, storm slabs and cornices are expected to develop. Watch for changing conditions Wednesday, steady southwest wind may form human triggerable slabs.

Confidence

Low - Due to the number of field observations

Weather Forecast

The system that has brought over 50 mm of rain to the forecast region should offer one last pulse Tuesday night. Wednesday marks the start of what looks to be a pretty significant drying trend as cold air begins to descend from the Arctic. No significant precipitation is expected for the duration of the forecast period and it looks like there is potential for clear skies by Sunday.TUESDAY NIGHT: Freezing level around 1300 m, moderate to strong southwest wind, 5 to 20 cm of snow possible with rain in the valley bottoms.WEDNESDAY: Broken cloud cover, freezing level holding around 1300 m, moderate southwest wind, trace of precipitation possible.THURSDAY: Scattered cloud cover, freezing level around 1000 m, light northerly wind, no significant precipitation expected.FRIDAY: Scattered cloud cover, freezing level around 800 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. 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 about 1800 m and left wet snow in place up to 2000 m. Strong to extreme wind on Monday and Tuesday 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 new snow now lies above a thin rime ice lens formed last 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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.