Avalanche Forecast

Issued: Apr 1st, 2012 10:32AM

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

Avalanche Canada ghelgeson, Avalanche Canada

Snow & wind may begin in earnest Monday afternoon. If it does, danger ratings will quickly rise.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Active weather continues for the next few days, culminating with a heavy hitting storm impacting the coast Monday/Tuesday. The current models show the storm breaking up on the coast leaving little precip for the interior. Any potential spill over into the coast would occur on Tuesday, so, we'll have a better handle on that tomorrow. Monday: Strong & well organized system impacts the coast, freezing levels rise to 1500 m ahead of the system. Precip should start up late in the day. 5 - 30 cm are expected late Monday. I know, that's a wild spread in values, but, that's how much disagreement there is in models at the moment. Tuesday: Significant precip may spill over into the interior, or it may not. Again, we should have a better handle on that tomorrow. Freezing level *may* climb as high as 1900 m Tuesday afternoon. Wednesday: Skies clear behind the passage of the cold front, freezing levels sink to the surface.

Avalanche Summary

Avalanche activity on the March 27th crust/facet layer continued Saturday. In the north of the region a size 3 was skier triggered on a south facing slope. In this same area a group of skiers were on an E-SE facing slope when the group felt a significant collapse which resulted in a size 2.5 avalanche being triggered from 300m away. Observers saw a bit more evidence of Friday's cycle which produced avalanches on all aspects to size 2.5, likely involving the Mar. 27th crust/facet combo.

Snowpack Summary

The most recent storm produced 35 - 60 cm of total snowfall. The storm snow rests on a layer that is proving to be quite volatile; the March 27th crust/facet combo. This layer, consisting of a melt freeze crust & small grain facets has been quite active over the last 48 hours. Avalanches have been remote triggered on this layer from hundreds of meters away. At lower elevations below treeline the crust was moist at burial which resulted in a more substantial bond.Spring the season has arrived, and it's not just calendar spring either, it's really felt different in the mountains recently. The snowpack is far from isothermic, but the mercury has climbed above 0 as high as 2500m recently. These warm temps have really helped to settle out what now is the mid pack. Slopes below 1000 m continue to experience little or no overnight refreeze (recovery).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, observers report that SW, S & SE slopes are being cooked almost instantly when the sun pokes out. W & E facing slopes are jumping in the mix now too & will be affected by the sun as we enter early April. 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. There hasn't been a deep slab avalanche in the region since Saturday March 24th. Deep slab avalanches may still be possible. I'm thinking of two 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 cornices are warming to their breaking point, then, there's no question, it's time to get off that slope.2. At this point I think the probability of human triggering the deep slab is very low. I don't really want to be proved wrong though, as the result would be large and destructive avalanche 1.5 - 2 m 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.

Problems

Wind Slabs

An icon showing Wind Slabs
Wind and storm slabs up to a meter in depth rest on the highly reactive Mar. 27 crust/facet combo. This problem is exacerbated in steep open terrain, especially on unsupported or convex slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Loose Wet

An icon showing Loose Wet
The sun will likely make an appearance Monday & it won't take long for the new snow to warm up which will produce pinwheels and rollerballs quite quickly. Loose snow avalanches to size 2 won't be far behind.

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Cornices

An icon showing Cornices
Very large unsupported cornices loom over many lee slopes. I suspect that many of them are nearing their breaking point. Cornices may fail without warning with the potential to trigger large destructive avalanches when they impact slopes.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

2 - 6

Valid until: Apr 2nd, 2012 9:00AM