Stevens Pass Avalanche Forecast
Jan 15th, 2020 10:00AM
The alpine rating is Wind Slabs., the treeline rating is , and the below treeline rating is Known problems include
Easterly winds may ruin the powder party on open slopes, creating unstable conditions on Thursday. Look for thickened slabs in exposed areas, and expect them to be larger and more dangerous the higher you go. Avoid trusting slopes steeper than 35 degrees that have drifts.
A cold, snowy regime continues. Over 6 feet of snow has fallen at Stevens Pass since the 10th, accumulating to over 4 feet of snow on the ground. A small (D1.5) recent storm slab was noted near Stevens Pass Mountain Resort on Wednesday on a southeast aspect at 5,600ft. The crown was roughly 8" deep and 50ft wide. Snowpack tests point to lingering potential instability at the old storm interface, buried on January 10th. This layer is now at least 4ft below the surface, and bears consideration before venturing into larger terrain.
With all the new snow, travel conditions are deep and challenging. Remember that even away from avalanche slopes, hazards exist like tree well falls and snow immersion suffocation. Make sure you’re informed and travel with a partner (www.deepsnowsafety.org). Expect the coldest temperatures of the season to date.
January 12th update: In the past week, there have been two fatal avalanche accidents to the east of NWAC's forecast area. One occurred near Kellog, ID and another outside of Baker City, OR. Local avalanche centers will perform accident investigations including final reports. You can find preliminary accident information at avalanche.org.
January 9th, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
As we said Happy New Year and rang in 2020, snow was turning to rain at many trailheads and lower elevation Passes, not exactly the fresh start winter recreationalists had in mind. The snowpack was already looking a little thin throughout the region, especially at lower elevations. Low snow in places like Snoqualmie Pass made backcountry travel difficult and hazardous. NWAC’s snow depth climatology report was showing snow depths 25-64% of normal to kick off the start of 2020.
Things can change quickly in the Pacific Northwest and they did as we entered an extended storm cycle between January 2nd to January 8th. Strong winds, fluctuating temperatures, and heavy precipitation offered few breaks in the weather over this period limiting observations and hampering travel. Despite periods of rain at lower elevations, most areas saw several feet of new snow with big jumps in total snow depths as a westerly storm track strongly favored the West Slopes of the Cascades and the Olympics for the highest precipitation totals.
Total Snow Depth (in) 1/2/20
Total Snow Depth (in) 1/8/20
Heather Meadows Mt Baker
Crystal Mt Green Valley
Paradise Mt Rainier
White Pass Upper
Mt Hood Meadows
We may have started with a shallow snowpack, but most locations increased their snowpack by 70% or more over this storm cycle!
During this extended and impressive storm cycle that included backcountry avalanche warnings, natural avalanches were reported in many areas Jan 6th-7th.
The Stevens Pass area was especially active over the period with over 100(!) avalanche observations made on the 6th and 7th. Professionals reported numerous avalanches in places that they hadn't previously observed avalanches and some paths avalanched multiple times in a 24 hour period. Observers reported a few very large (size D2.5-3) avalanches, originating at upper elevations with deeper crowns that likely formed from wind drifting. Topping off an active couple of days, warming temperatures lead to a widespread loose wet avalanche cycle.
The southern Washington Cascades, the Wentachee Mountains and Mt. Hood either saw less precipitation, warmer temperatures leading to more rain than snow, or some combination of the two and ended up with relatively less active avalanche conditions than areas further north.
A large natural avalanche on Rock Mountain near Berne along Hwy 2 east of Stevens Pass that released Jan 6th or 7th. Photo: Josh Hirshberg 1/7/20
Many small storm slabs released in the Crystal backcountry 1/6-1/7. Pinwheels in the photo suggest loose wet avalanche activity occurred when temperatures rose above freezing and snow turned to rain.
Another active and colder weather pattern is on it’s way. Enjoy yourself out there and be sure to check the forecast before heading out. Remember, NWAC is a community-supported avalanche center and when you submit an observation you make the forecast better!
It’s getting deeper! Photo: Jeremy Allyn
By the time morning rolls around the active wind loading may be over, but firm slabs may be prime for human triggering. East and southeast winds are funneling through the pass this evening, forming wind slabs in somewhat unusual places. The low density snow will be easily transported. In addition, there are previously formed slabs from northwest winds that will be hidden underneath new snow. You are most likely to trigger wind slabs in recently formed drifts in open terrain that is exposed to easterly winds. Look for hollow, drum like snow as you transition onto exposed slopes. If you see cracking and feel slabby snow, avoid slopes steeper than 35 degrees.
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Valid until: Jan 16th, 2020 10:00AM