Cascades - North West Avalanche Forecast
Jan 13th, 2020 11:03AM
The alpine rating is Storm Slabs., the treeline rating is , and the below treeline rating is Known problems include
Dangerous avalanche conditions will persist for another day at mid and upper elevations following a huge storm cycle. Assume you can trigger a large avalanche on steep open slopes with recent wind drifted snow. In sheltered areas, think about the consequences of a loose dry avalanche near terrain traps.
An active storm cycle with over 4 ft of snow in the West North zone is finally winding down. Low density snow piled up more than expected today, but the new snow was measured in inches instead of feet. Winds eased and temperatures plummeted into the teens as colder air filtered in. Widespread natural and human triggered avalanche activity was reported over the weekend with some slides triggered from lower angeled slopes (observation). While large avalanches were triggered during Monday morning's control work by Mt. Baker pro-patrol, professionals found storm snow layers becoming less likely to trigger later in the day.
With all the recent snow deep snow hazards are real. Before heading out, learn about tree well or snow immersion suffocation risks and travel with a partner (www.deepsnowsafety.org). Also, be prepared for the coldest temperatures seen this winter over the next several days.
A natural avalanche (D1) that failed about 1ft deep within new snow in Swift Creek on a NE aspect at 4600ft. 01/12/20 Photo: Robert Hahn
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
Observations from Monday in non-wind affected terrain show storm instabilities healing and the chances of triggering a storm slab avalanche decreasing. It's at higher elevations where we think you can still easily trigger a large avalanche on steep open slopes with wind drifted snow. Cold temperatures will help preserve sensitive interfaces within the upper snowpack.
Continue to make conservative terrain choices and avoid large open slopes steeper than 35 degrees where you see signs of wind transported snow such as cornices, and pillow-like drifts of snow. Give fresh cornices a wide berth when traveling along ridgelines and avoid traveling on slopes directly below them.
With cold temperatures and lots of new snow, you will find wind-sheltered areas with deep uncohesive loose snow. On very steep slopes loose snow avalanches or “sluffs” can be large enough to push you over or knock you into tree wells or open creeks.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Valid until: Jan 14th, 2020 11:03AM