Avalanche Forecast
Issued: Mar 19th, 2020 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
Continue to weigh the consequences of loose wet avalanches on steep sunny slopes near terrain traps. You can avoid this problem by traveling earlier in the day when the snow surface is firm or by choosing lower angled supported slopes as temperatures rise and wet snow conditions develop.
Summary
Snowpack Discussion
March 19, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
This week brought a whirlwind of change to our community, the mountains, and the snowpack. It’s mind-boggling to think of how everything changed in just a few short days. Last weekend, a strong winter storm brought frigid temperatures and fluffy powder to many mountain locations. While the calendar read March, conditions felt more like mid-winter. The hands-down winner during this storm was Mission Ridge and the surrounding mountains. As the skies cleared, sunshine and warm temperatures settled into the northwest. Now we’re in the midst of a prolonged spring-like pattern as the snowpack slowly transitions. The biggest change this week may be the impact of the Coronavirus on our community, local mountain operations, and backcountry travel. We continue to work through and adapt to all of these changes in our daily lives as we mark the first official day of spring.
Wenatchees for the Win
We all know the Wenatchee mountains can receive serious dumps of snow, but this season conditions had been fairly dry. Prior to this past week, Snotel sites and weather stations in the Wenatchees reported only about 65% of average snow depth for the season. A strong low-pressure system began impacting the Pacific Northwest last Friday. However this storm did not follow the usual storm track, it meandered south off the coast, spinning moisture around its center, and sending snow into the Cascades from the SE. When moisture wraps around and approaches our mountains from this direction, it can pack quite a punch along the eastern slopes of the Cascades and in particular the Wenatchees. Early Friday morning, Mission Ridge entered a near 48hr stretch of continuous snowfall. A secondary impact of this low-pressure system was an influx of cold Canadian air which dropped snow levels to near sea level for nearly all locations. The cold air mass combined with the unusual storm track led to substantial accumulations of light fluffy snow; Mission Ridge quickly stacked up over 2ft of very light powder. This new snow and strong winds produced some of the spiciest avalanche conditions for this season in the East Central zone. Numerous natural and human triggered avalanches occurred during and following the storm, including some remotely triggered slides.
Skier triggered avalanche on the Diamond Head in the Wenatchee Mountains. NW, 5200’ 3/14 Photo: Adam Butterfield.
Other locations in the region only added a few inches to their snow totals for the season. The position of the storm only brought dribs and drabs to the mountains from about Hwy 2 and south. A few standouts further south managed to ring out around a foot (Mt St Helens, White Pass, and Paradise). Strong easterly winds in most areas significantly redistributed the new snow and resulted in reports of numerous natural and human triggered slab avalanches Saturday and Sunday.
Natural wind slab avalanche on Mt St Helens. W 5500’ 3/14: Photo Nate Berry
Spring has Sprung
Thursday the 19th ushered in the first official day of spring. All winter, we’ve seen storms creating sometimes unique and occasionally similar snowpacks and avalanche conditions for each of our forecast zones. Following the storm last weekend, a sunny and warm springtime pattern took hold of the region. As it did so, it brought with it a prolonged gradual warm-up and loose wet avalanche cycle. Consequently, differences formerly found in each region slowly resolved as the mountains transitioned into spring.
A natural loose wet avalanche near Washington Pass, Cutthroat Peak. 3/17. Photo: Gus Goldman
Two items still stand out about this spring transition. 1: the snowpack has not fully moved into a spring-like state. You can still find pronounced cold dry layers and firm icy crust in many areas. 2: We have not seen a spring “shed” cycle yet, where several large natural avalanches occur as the snowpack adjusts to percolating water and warmer temperatures. Forecasting spring shed cycles can be difficult, and it's still unclear when or even if a larger natural wet cycle will occur.
You can continue to support your community-based avalanche center by submitting observations.
Stay safe, stay healthy, and thank you for all your support.
Dallas Glass
Problems
Loose Wet
Another day of mostly sunny skies paired with mild spring temperatures will hit the repeat button regarding what to look for and think about avalanche-wise in the Mt. Hood area.
Generally safe conditions are expected with the exception of consequential terrain where you may trigger a small loose wet avalanche. The likelihood of triggering a loose wet avalanche will be lowest in the morning and increase during the day relative to the aspect, elevation, and the extent of the overnight snow surface refreeze. Look for signs that you could trigger a loose wet avalanche such as rollerballs forming in the recent snow, wet surface snow deeper than your ankle (greater than 4"), or if you observe natural loose wet avalanches releasing.
When you see these signs move to lower angled terrain or slopes with a firmer surface. Loose wet avalanches are often surprisingly powerful -- use extra caution near terrain traps like open creeks and cliff bands. As the sun moves across the sky, consider that the firm steep slopes you crossed in the morning may not be safe to cross in the afternoon.
Exercise normal caution around cornices. Give them a wide berth when traveling along ridgelines and don't linger below slopes with large cornices as the day warms. Realize that while you may be in the shade, cornices above you may still be receiving direct sun.
If you're out, please take a moment and tell us and the community what you see!
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: North East, East, South East, South, South West, West, North West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 20th, 2020 11:00AM
