Avalanche Forecast
Issued: Mar 18th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
wlewis,
Avalanche Canada
Steer clear of steep and consequential slopes, give the snowpack time to adjust to the new load of recent heavy snow and warm temperatures.
Watch for reactivity in wind loaded features, and be aware of the buried layers potential to produce large, wide propagating avalanches.
Summary
Confidence
Moderate
Avalanche Summary
The storm produced avalanche activity up to size 3 in Haines Pass with impressive propagation in large connected features on north facing slopes (lee to southerly winds). White Pass also saw natural avalanche activity but to a lesser extent likely due to warm temperatures encouraging bonding.
Storm snow is expected to remain reactive to human triggers in wind loaded features.
Snowpack Summary
Around 50 cm of storm snow has fallen around White Pass, with lesser amounts as you move east. Southerly winds have built deeper deposits on north facing terrain features near ridges.
In Haines Pass upwards of 50 cm of storm snow fell, with rain on snow occurring below 700 m. Storm totals also taper inland here, with winds rapidly redistributing snow and leaving soft snow to be found in sheltered gullies and side valleys.
In all areas, storm snow overlies previously wind affected snow (sastrugi) in exposed areas and faceted snow in sheltered features. Warm temperatures have helped storm snow to bond to these weaker surfaces, but reactivity may remain in specific terrain features.
A buried weak layer of surface hoar can be found about 80 cm deep in Powder Valley, Tutshi, and Paddy Peak areas, 150 to 200 cm around White Pass and 80-200 cm deep in Haines Pass. This layer is most prominent on northerly slopes sheltered from the wind. On other aspects, this layer is a hard melt-freeze crust with weak facets around it. To date this layer is has been most problematic in alpine terrain.
The remainder of the middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack, particularly in thin snowpack areas.
Weather Summary
Saturday Night
Mostly cloudy with strong southerly winds. Freezing levels drop below 500 m. Snowfall begins - up to 5 cm for White Pass, and around 15cm for Haines Pass.
Sunday
Cloudy with moderate southerly winds. Up to 5 cm of snow. Freezing levels reach 1000 m.
Monday
Cloudy with light to moderate southeast winds. Up to 5 cm of snow. Freezing levels reach 1000 m.
Tuesday
Mix of sun and cloud with light southerly winds. No snow expected. Freezing levels remain around 500 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Conditions may have improved, but be mindful that deep instabilities are still present.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Problems
Wind Slabs
Up to 50 cm of storm snow with strong southerly winds has formed reactive wind slabs on north and west facing terrain features. Watch for wind loading as you travel through terrain, local wind patterns have varied from southerly in White Pass to more easterly in Haines Pass.
While warm temperatures have encourage this snow to bond, storm snow sits over weak surfaces and reactivity may linger.
Fresher wind slabs are likely to be found in the Haines Pass area, as snowfall continues.
Aspects: North, North East, East, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar and/or faceted grains around a hard crust sit in the mid snowpack. This layer is buried around 80 cm in the eastern portions of the region and up to 200 cm around White Pass and Haines Pass.
This layer has previously produced widely propagating avalanches in alpine terrain and it is capable of being remotely triggered from a distance. The most likely area for riders to trigger it is in wind-sheltered, north-facing terrain, and in rocky terrain where the snowpack is thin.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 19th, 2023 4:00PM
