The heat is on and the game is changing. Direct sun and steadily warming temperatures are expected to destabilize the upper 20 to 30 cm of snow and a natural avalanche cycle is possible. Look up and avoid travel under avalanche paths and cornices.
Weather Forecast
The first big warm up of the season really begins to flex on Sunday. Say goodbye to any kind of temperature driven overnight re-freeze for the next few days. This weather event is going to have a pretty significant impact on our snowpack.SATURDAY NIGHT: Freezing level rising to 2000 m, light northwest wind, no significant precipitation, no overnight re-freeze.SUNDAY: Clear skies, light northerly wind, freezing level rising to near 3000 m, no precipitation, no overnight re-freeze.MONDAY: Clear skies, light southeast wind, freezing level holding at 3000 m, no precipitation, no overnight re-freeze.TUESDAY: Clear skies, moderate southeast wind, freezing level holding at 3000 m, no precipitation, no overnight re-freeze.
Avalanche Summary
No new avalanche activity to report from the last few days.
Snowpack Summary
Wind slabs are likely done at this point, zapped of their strength by time and warming.For Sunday, we're most concerned about the upper 20 to 30 cm of snow that sits on crust on steep south slopes and possibly weak surface hoar crystals on sheltered and shaded slopes.The bigger questions are deeper in the snowpack. A layer of weak and sugary faceted grains sits on a melt-freeze crust about 50 to 120 cm deep. The layer is likely most prominent in the North Shore Mountains and on north aspects. After Saturday night, we're not expecting an overnight re-freeze for at least a few nights. That's going to allow the snowpack to warm and start freeing up a lot of water which acts like lubrication. When it doesn't freeze overnight, this process gets turbo-charged. How many hot days and warm nights will it take to wake up the more deeply buried weak layers? We're not sure, but now is probably a time to let the mountains do their thing from afar and check back in when the freezing level returns to seasonal norms which could happen by next weekend.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.