The Sawtooth Avalanche Center has issued a special avalanche bulletin for the Wood River Valley and surrounding mountains amid an ongoing heat wave pushing daytime highs 10 to 20 degrees above normal.
The bulletin—issued Friday afternoon and set to expire Friday, May 5—denotes “unusual and dangerous” avalanche conditions occurring outside of the Avalanche Center’s regular daily forecast season, which ended on April 16.
“Avalanches could impact roadways, trails, and structures in the valley bottom,” the bulletin reads. “They may be large enough to dam rivers, snap trees, and destroy a wood frame house.”
Temperatures in the south valley reached 76 F on Saturday, while temperatures in Stanley, Ketchum and Sun Valley clocked in closer to 70 F. Daytime highs across the valley should stay above the 50 F mark through Friday, according to the Weather Service.
The bulletin applies to the “Sawtooth, Smoky, White Cloud, Boulder, Soldier, Pioneer, and southern Salmon River Mountains,” including the Banner Summit, Stanley, Atlanta, Smiley Creek and Galena Summit areas and all cities in Blaine County.
Anyone recreating in the backcountry should stay off and away from the bottom of slopes steeper than about 30 degrees, the Avalanche Center stated.
In Friday’s avalanche bulletin, Avalanche Specialist Ethan Davis explained that above-freezing overnight temperatures and possible rain showers on Monday, Thursday and Friday will encourage meltwater to infiltrate weak, dry layers of snowpack, “weakening the bond of the overlying slab to release a wet slab avalanche.”
“As more of the snowpack turns to mush, these relatively thin slides will gouge deeper, creating larger and more dangerous avalanches,” he stated. “These slides have the potential to be massive, ripping what's left of the season's snowpack from the mountain. Wet avalanches are deceivingly powerful.”
The Sawtooth Avalanche Center has reported more than 102 avalanches so far in April, with the largest “D3” slides concentrated around Galena Peak, Pole Creek, Alturas Lake, Boulder Peak, Easley Peak and the Salmon River Headwaters.
Davis noted that he and Avalanche Specialist Jon Preuss observed “numerous wet loose avalanches” on Thursday on “very steep, upper elevation slopes of the Boulders, Smokys, and Sawtooths.
“This heatwave will be 10 degrees warmer and last three times longer than the warm-up that produced a widespread wet avalanche cycle on April 9th and 10th,” Davis stated. “Higher sun angles, longer days, and the threat of rain will only make matters worse.”
Davis said predicting the onset of avalanche activity will be “next to impossible,” but northern-facing slopes, including the avalanche paths out Warm Springs Road, are more prone to slides.
“Avalanches can occur at any time until the snowpack refreezes. Simply getting up early in an attempt to beat the heat will not significantly reduce your risk,” he stated. “Given the uncertainty associated with wet avalanches, the prudent move is to put our mountain objectives on hold while we wait for cooler weather.”
To submit an avalanche observation to the SAC, fill out an online observation form here or text 208-481-5921. Details on recent avalanche activity can be found here.
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