Northwest Coastal Avalanche Forecast

Issued: Nov 24th, 2021 4:00PM

Thu Nov 25th Current Conditions
Alpine High Treeline High Below Treeline Moderate
Fri Nov 26th 2 Day Outlook
Alpine Considerable Treeline Moderate Below Treeline Low
Sat Nov 27th 3 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Moderate

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

Avoid travelling in avalanche terrain on Thursday. Large destructive avalanches are likely due to intense precipitation and wind.

Summary

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

An intense frontal system is crossing the region on Wednesday night with heavy precipitation, strong wind, and mild temperatures.

WEDNESDAY NIGHT: Precipitation intensity peaks overnight with a total of 30-50 mm possible, freezing level around 1000 m will result in snow at upper elevations, extreme southwest wind with gusts to 120 km/h.

THURSDAY: Precipitation continues with another 15-25 cm of snow above 1200 m and rain below, strong southwest wind with gusts to 90 km/h, freezing level around 1200 m.

FRIDAY: Mostly cloudy with some light flurries, moderate southwest wind with gusts to 50 km/h, freezing level at valley bottom with treeline temperatures around -5 C.

SATURDAY: Next system arrives with 15-25 cm of snow by the evening, strong southwest wind, freezing level climbs to 800 m with treeline temperatures around -2 C.

Avalanche Summary

Last weekend's storm resulted in a widespread avalanche cycle with numerous reports of size 2-3 storm slab avalanches at upper elevations and wet loose avalanches below treeline. These avalanches were reported at all elevations and aspects.

Expect a similar avalanche cycle to start on Wednesday night and continue into Thursday with the current weather system.

Snowpack Summary

40-60 cm of new snow will likely accumulate in the alpine by Thursday afternoon. Somewhere between 1000 and 1200 m the snow will transition to rain, resulting in a relatively narrow elevation band with dramatically different conditions.

A progression of intense storms over the past month has resulted in impressive snow depths, with total depths at treeline ranging from 200 to 250 cm. The snow from these storms has generally been strengthening and bonding quickly. A prominent crust from early November can be found in the lower snowpack, but does not appear to be a problem. Many areas below treeline are still below threshold depths for avalanches.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Remember that the snowpack will be significantly different at higher elevations than lower down.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Very Likely

Expected Size

2 - 3

Heavy precipitation and extreme wind will drive a natural cycle of storm slab avalanches on Thursday. Human triggering is very likely under these conditions. At lower elevations there may be a mix of wet loose and thinner storm slabs.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Nov 25th, 2021 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.