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Avalanche Forecast

Archived

Mar 27th, 2012–Mar 28th, 2012

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

Regions

South Columbia.

Confidence

Fair - Intensity of incoming weather is uncertain on Thursday

Weather Forecast

The Gulf of Alaska drives a relatively moist weather pattern for the second half of the week. The region should pick up around 5 cm Tuesday evening along with moderate southerly winds. Wednesday: Another 5 cm of snow are expected. Freezing level is relatively well behaved staying around 1500 m. Winds out of the SW, light at treeline, moderate in the alpine. Thursday: 5 - 15 cm expected above 1000m. Winds SW, mod at treeline, strong at ridge top. Friday: Snowfall starting late in the day, 10 - 15 cm expected by Saturday morning.

Avalanche Summary

Numerous point releases out of steep solar aspects where observed. No large avalanche activity reported from the region.

Snowpack Summary

Spring the season has arrived, and it's not just calendar spring either, it's really felt different in the mountains the past week. The snowpack is far from isothermic, but the mercury has climbed above 0 as high as 2500m over the last 7 days. These warm temps have really helped to settle out the upper snowpack. Professionals throughout the region are reporting a very well settled & firm upper snowpack with minimum concerns in the upper 150cm. The spring sun is increasing in strength as each day grows by a few minutes. It takes very little time for S, SE & SW aspects to feel the heat of the sun now. W & E facing slopes are just starting to be affected by the sun as we head into the tail end of March.The effect of the sun becomes very important at this time of the year. We're expecting 5 - 10 cm of snow above 1500 m the next few days. As soon as the sun comes out, watch for roller-balling & pin-wheeling to start surprisingly quickly. Wet point release avalanches won't be far behind on slopes receiving direct sun.There's a lot of strong snow between recreationists and the February surface hoar layers and it's been a few days since there was a large deep avalanche in the region. That being said, it could still be triggered. I'm thinking of three different scenarios at the moment: 1. The most likely scenario is a large cornice or icefall failure impacting the slope below and producing a very large avalanche. Managing this piece of the hazard puzzle is done by monitoring what's happening above you. Cornices or slopes receiving direct sun are suspect. If you feel like there's a question as to whether or not a piece of cornice is warming to its breaking point, then, there's no question, it's time to get off that slope. 2. Just last weekend an experienced party remote triggered a very large avalanche in Glacier Park near Mt. Tupper. This makes me think that it may still be possible for skiers or sledders to trigger very large avalanches failing 1.5 - 2m in depth. The most likely location for this type of failure is where the snowpack goes from thick to thin. This is most likely near ridge crests, the edges of slopes and especially around rock outcroppings. 3. While I don't foresee it occurring in the next few days, a slope that does not experience an overnight refreeze is suspect for producing large avalanches. This is something to think about as we flip our calendars to the April page.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.