Snow & wind may begin in earnest Monday afternoon. If it does, danger ratings will quickly rise.
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
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.