The Bottom Line: Firm surface crusts exist on all aspects and elevations after several days of clear very mild weather, limiting the avalanche danger. Another sunny and warm day Monday will compete with increasing easterly winds limiting snowmelt and the Wet-Loose avalanche potential. Watch for deeper melting surface snow on steep sun-facing slopes sheltered from the wind.
Snow and Avalanche Discussion
A nearly 1-inch thick ice crust broke down on Saturday and Sunday with very warm temperatures and sunshine. Hard surface crusts also made for hazardous conditions from uncontrolled falls, especially early in the day. These conditions should continue Monday, especially early in the day before crusts soften.
Recent cornices have been evident 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 Monday as the sun begins to warm them.
Mon 28th Jan 13:28
- Kenny Kramer
Weather Synopsis for Monday night through Wednesday
A ridge of high pressure will remain centered offshore on Monday night and weak gradually through Wednesday, maintaining fair and dry weather. Surface high pressure has strengthened east of the Cascades Monday causing increasing easterly winds across the Cascade crest and through Stevens, Snoqualmie and White pass. Surface high pressure and cooling easterly winds have strengthened a temperature inversion with below-freezing temperatures returning to the passes and lower elevation areas, especially along the east slopes.
Some high clouds will continue to spill over the ridge at times through Wednesday, however, plenty of sunshine will persist both Tuesday and again Wednesday.
The current weather pattern typically causes extensive low clouds and fog along the east slopes and valleys, however, a lack of sufficient low-level moisture is limiting clouds and fog to just patchy areas.
The moderate easterly winds Monday should gradually subside Tuesday through Wednesday, allowing for warmer temperatures.
The next approaching weather system expected to undercut the offshore ridge has been consistently forecast to move southward well offshore Tuesday and head towards southern California Wednesday, missing the region entirely.
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 and sheltered from increasing easterly winds. 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.