The Bottom Line: You can trigger a Loose Wet avalanche where direct sunshine and very warm temperatures combine with light winds to break down the surface crust. Wet snow that you can penetrate to ankle deep or greater should encourage retreat to slopes less than 35 degrees or less sun-affected aspects and away from terrain traps or terrain hazards.
Snow and Avalanche Discussion
We didn’t expect the 0.5-1” thick water ice crust to break down on Saturday, but it did. Slide for life conditions were a very real threat on Mt. Hood on Friday and on Saturday, an observer reported soft surface conditions on a variety of sun-influenced aspects that were deep enough to produce a loose wet avalanche. A crust should re-form Saturday night and we expect it to break down once again with similarly warm and sunny weather present once again, assuming winds stay light. You may encounter very slick or soft snow surfaces and winds are the major determining factor.
Cornices have been growing in the terrain. You are most likely to find them overhanging northerly slopes or on the edge of gully features. Don’t linger below these cornices on Saturday as the sun begins to warm them.
Sun 27th Jan 06:32
- Kenny Kramer
Weather Synopsis for Sunday & Monday
A strong ridge of high pressure will remain centered just offshore Sunday and Monday. This will maintain mostly fair weather and mild temperatures at higher elevations.
A shift from westerly flow across the Cascades and passes to easterly winds will occur Sunday evening and strengthen Monday. This will strengthen the inversion and maintain cooler temperatures at lower elevations as well as increasing low clouds and fog near the passes Monday.
Temperatures remain very mild for mid-winter under the strong high pressure with several NWAC stations in the low to mid 40's early Sunday morning.
Sat 26th Jan 09:00
The late January pause...
Now that we’re well into winter and in the midst of a prolonged period of quieter weather, this is a good time to assess the current snowpack. Most areas are hovering around 75% of average snowpack depth for the season to date. Many of this season’s storms have brought at least some rain to mid elevations at the passes and west of the Cascade Crest. Multiple periods of cool, clear weather formed persistent weak layers.
A prolonged period of warm quiet weather followed a storm on January 22-23rd that impacted most of the region. This weather system changed snow at the surface of the snowpack, drove an avalanche cycle, and tested or changed the latest persistent weak layers. The storm ramped up late on the 22nd in most areas. Intense precipitation (mostly snow) fell by dark with strong wind and warming temperatures. In the early morning hours of the 23rd snow switched to rain at the passes and western zones. Cold air to the east maintained low-density snowfall at most locations well east of the crest. In some areas, especially east of the crest, a new weak layer may have been buried at the January 22nd interface.
January 23rd avalanche cycle
The bulk of recently reported avalanche activity occurred on January 23rd with high precipitation rates and wind loading in the early morning hours or with liquid water in the snow from rain or warming and sun during the day.
At the passes and in the western zones, reported avalanches were generally running either at the new/old snow interface or within the new snow. Observers reported a mix of soft slab, wet loose avalanches from near and below treeline with a few reports of shallow slabs above treeline. As of January 24th observations at upper elevations have been limited, due to lack of visibility and access.
In the eastern zones at areas like Washington Pass, Icicle Canyon, and the Wenatchee Mountains, some reported slab avalanches were confirmed or suspected to have involved persistent weak layers. Most notable is the January 17th surface hoar/near surface facets. There were a few reports of widely propagating avalanches, up to destructive size 3. Wind loading was a factor in many avalanches that released at upper elevations. Observers reported a widespread point releases on steep sunny slopes in the new snow where skies cleared on the 23rd.
Persistent Weak Layers (PWLs)
The latest round of snow, rain, and warming that tipped the balance of the snowpack was a good test of existing persistent weak layers. While the ever-changing snowpack keeps us busy tracking changes, some trends are apparent.
West Slopes and Passes: With a few exceptions, persistent weak layers have gained enough strength through rounding or melt-freeze to no longer be a concern for triggering avalanches. The main uncertainty lies with the January 17th surface hoar at upper elevations near Stevens Pass. This PWL is no longer a concern below treeline or in other zones. It appears that surface hoar generally wasn’t a player in avalanche activity near and west of the Cascade Crest. At low elevations, it has either been wetted by rain or is capped with crusts and moist snow. There’s reason to prioritize other issues, like challenging travel conditions, below treeline.
Eastern Cascades: Triggering avalanches on persistent weak layers is possible east of the Cascade Crest. How much of a concern and exactly which PWL depends on where you are, north to south and east to west, in the range. The January 17th surface hoar/near surface facets is the main concern in the upper snowpack. Areas of shallower snowpack that lie further east of the Cascade Crest will have weaker snow and more pronounced weak layers in the mid to lower snowpack. In the Wenatchee Mounains you may find another layer of surface hoar (January 3rd) in the middle of the snowpack as well as weak facets near the ground. In places, like Washington Pass, the January 22nd surface hoar may become an issue with future storms.
We expect the potential to trigger a Loose Wet avalanche on slopes steeper than 35 degrees that are experiencing direct sunshine. If you experience loose snow deeper close to your boot top, seek lower angle terrain or adjust your aspect. These avalanches are most dangerous where they can push you into a terrain trap, over a cliff, or into a boulder, or a tree.
East, South East, South, South West, West.