Avalanche Forecast Snoqualmie Pass

Date Issued: Valid Until:

Josh Hirshberg,

Avalanche Forecast

Sat Jan. 26th · 6:00PM

Alpine

Danger Ratings Moderate

Treeline

Danger Ratings Low

Below Treeline

Danger Ratings Low
Wind Slabs Wind Slabs

Alpine

Danger Ratings Moderate

Treeline

Danger Ratings Low

Below Treeline

Danger Ratings Low
The Bottom Line: Expect the warmest temperatures of the winter, so far. Warming, sun, and uncertainty of the snow layers at upper elevations will maintain heightened conditions. If you are heading to higher slopes, use caution on slopes 35 degrees and steeper.

Snow and Avalanche Discussion

With warming and sun, uncertainty about the snowpack is increasing. Most loose wet avalanches you will see are a few days old. Watch for wet avalanches if you see soft, wet snow on sunny slopes and at low elevations. The lower elevation snowpack continues to creep and glide under the weight of recent rains. While no glide avalanches have been reported, they are on our mind. If you see crevasse like features on a slope, limit you exposure by avoiding traveling on or below these areas.

Expect difficult travel conditions at lower elevations including breakable crust, wet heavy snow, and open creeks.

Evidence of Wednesday’s avalanche cycle is easy to find. Debris from several large and very large avalanches Has been reported around the Alpental Valley. Check out the Regional Synopsis for more details of recent avalanches and conditions.

Very large natural avalanches on Chair Peak from Wednesday’s avalanche cycle: Photo: Jeremy Allyn

Weather Forecast

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.

Regional Synopsis

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.

Icicles hanging off of a snow feature are evidence of recent rain and daily temperatures swings. Stevens Pass. Photo: Josh Hirshberg


Recent conditions

 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.

Wet loose avalanches on Mt Herman, near Mt Baker from 1/23. Photo: Lee Lazzara


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.

A highlighted crown of a slab avalanche in Wenatchee Bowl, adjacent to numerous loose avalanches. Avalanches ran on January 23rd in recently fallen snow. Stevens Pass. Photo: Josh Hirshberg


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.

A slab avalanche on 1/23 (likely ran on the January 17th surface hoar) in Varden Creek drainage, near Washington Pass. The crown extends out of the photo, over 300ft wide.


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.

Problems

Wind Slabs

Wind Slabs

Recent storm snow should be gaining strength. However, we have a high degree of uncertainty at higher elevations. You may still trigger lingering storm slabs on very steep slopes, near convex rollovers, or in unsupported terrain. If you see evidence of wind drifted snow, storm slabs in these areas may be deeper and easier to trigger. A little patience and caution will go a long way if you are traveling into alpine areas or more remote locations.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 2