Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Wednesday, April 1st, at 7:30 a.m. Big Sky Ski Patrol in cooperation with the Friends of the Avalanche Center sponsor today’s advisory. This advisory does not apply to operating ski areas.
A moist northwest flow continues to give us snow. Three to five inches fell over most of our area with seven to nine inches accumulating around Big Sky and West Yellowstone. Mountain temperatures are in the teens and will rise into the low 20s today. Ridgetop winds are blowing westerly at 20-25 mph and will switch to the southwest later tonight. Another inch or two may fall today, but unsettled weather will bring even more snow Thursday and Friday. And that’s no April Fools joke.
The Bridger, Gallatin and Madison Ranges, and the Lionhead area near West Yellowstone:
Folks got out playing yesterday and sent in some great observations. First off, the winds blew at the ridgetop level creating wind slabs that were sensitive to triggering. These soft slabs broke 10 inches deep and were confined to the ridges. Skiers enjoying the last day of access up Hyalite found stable conditions on a snowpack deeper than most avalanche probes. Overall, thinner areas tend to be weaker. No matter if you’re in the Bridgers, on Mt. Ellis, around Beehive Basin or West Yellowstone, thinner slopes will be more unstable. Our stability tests and last week’s avalanche activity around Bozeman and Big Sky bear this out. I consider a three to five foot deep snowpack to be thin for this late in the season.
Weak snow two feet off the ground can still fracture, although we’re not finding it connected over a wide area—it’s more slope specific. I consider this good news since there’s many slopes to safely play on, but it’ll take some investigative work to find them. Signs of instability like collapsing and cracking are currently rare. It takes many pieces of evidence to determine if a slope is stable, but only one to tell you it’s not. One bad stability test, one huge collapse, one avalanche is all the information you need to notch it back and stick to lower-angled terrain.
Moderate winds last night continued unabated. These winds are responsible for our primary and most obvious avalanche concern—steep, wind-loaded slopes. Pillows of wind blown snow are mostly confined to higher elevation ridgelines. Two to three feet has fallen since Sunday providing a war chest of snow ready to be blown into drifts. For today, the avalanche danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all other terrain.
The mountains around Cooke City and the Washburn Range:
The mountains around Cooke City have gotten snow and wind like the rest of our area. However, because these mountains lack the weak layer found elsewhere, avalanche activity will be limited to the new, wind blown snow. Above treeline the winds have set the stage for human triggering. As tempting as it is, be careful highmarking or skiing on these open, wind affected slopes. For today, the avalanche danger remains CONSIDERABLE on all wind-loaded slopes. On slopes not affected by the wind a MODERATE danger exists if it’s steeper than 35 degrees and LOW everywhere else.
Mark will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or send us an email with your observations. You can reach us at 587-6984 or at mtavalanche@gmail.com.
