Advisory for Fri Nov 17, 2017

Good morning. This is Eric Knoff with early season weather and avalanche information from the Gallatin National Forest Avalanche Center on Friday, November 17th at 6:00 a.m. This information is sponsored by The Friends of the Avalanche Center and Montana State Parks. We will update this bulletin when conditions change. The GNFAC will begin issuing daily advisories on Friday, November 24th.

Mountain Weather

Over the past 24 hours the mountains around West Yellowstone and Cooke City picked up over a foot of new snow. The mountains around Big Sky including the northern Gallatin Range squeezed out 2-3” while the Bridger Range remained mostly dry. At 5 a.m. temperatures range from the upper teens to mid-20’s F and winds are blowing 15-30 mph out of the W-SW. Today, skies will remain mostly cloudy and light snow showers will linger in the mountains south of Bozeman, although no real accumulation is expected. Highs will warm into the upper 20’s to low 30’s and winds will gradually decrease blowing 10-20 out of the W-SW. A weak ridge of high pressure builds over the area tonight and this weekend looks to be mostly dry.

Snowpack and Avalanche Discussion

All Regions

The current storm has heavily favored the mountains around West Yellowstone and Cooke City, which have picked up over a foot of high density snow totaling 1.5 to 2” of SWE (snow water equivalent). This rapid and heavy load will be applying significant stress to any weakness in the snowpack. Stress will be especially concentrated on wind loaded slopes, which will likely produce human triggered avalanches today. Natural avalanches will also be possible, so carefully evaluate terrain and avoid traveling underneath large, steep slopes.

Winds have blown predominately out of the west-southwest, making slopes facing the east half of the compass most susceptible to heavy wind loading. However, all slopes have the potential to hold wind drifted snow, especially at higher elevations. Obvious signs of instability such as cracking and collapsing are obvious clues the snowpack is unstable. Also, keep an eye out for large cornices along the ridgelines. These are key indicators heavy wind loading has taking place. Yesterday, skiers up Beehive Basin near Big Sky observed a natural cornice failure that triggered as small slab avalanche on the slope below (photo). Today, I expect cornices and slopes below cornices to remain highly sensitive to human triggers.

Outside of wind loaded slopes, the snowpack has a few lingering instabilities. The main concern is the interface between the old snow surface (Sept.- Oct. snow) and the 2-4’ that has fallen over the past few weeks. On Wednesday, Alex and I got multiple ECT’s to propagate on this interface at higher elevations in the northern Bridgers (video). A large natural avalanche outside of Cooke City a week ago is a good example of what’s possible when slides fail on layers deeper in the pack (photo). This interface isn’t unstable on all slopes, so it’s worth digging a snowpit and doing a stability test to assess the relationship between all layers in the snowpack.

We are still collecting snowpack data from around the advisory area and will begin issuing danger ratings when we start daily advisories a week from today.

If you get out and have any avalanche or snowpack observations to share, drop a line via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Get Avalanche Smart – Episode 2: Don’t Be Like Dick

The Friends of the Avalanche Center present the second of 4 short films promoting avalanche education. Dick Aspen and Doug Chabot star in this episode to encourage you to “get the real forecast” VIDEO.

Upcoming Avalanche Education and Events

Events and Education Calendar

BUTTE

Tonight! Avalanche Awareness, 6-7:30 p.m., Butte, MT

HELENA

18 November, Avalanche Awareness and Beacon Practice for Snowmobiles, 9 a.m. at Montana Boat Center, Helena

7 December, Avalanche Awareness, 6-7:30 p.m. at Basecamp, Helena

BOZEMAN

6 December, Avalanche Awareness, 6-7:30 p.m. at REI Bozeman

7 December, Avalanche Awareness and Beacon Practice, 6-8 p.m. at Beall Park, Bozeman

Nov. 29, 30 and Dec. 2, 3 or 9, Introduction to Avalanches w/ Field Day, Info and Register Here

Jan. 12 and 13, Companion Rescue Clinic, Info and Register

Jan. 17, 18 and 20 or 21, Introduction to Avalanches w/ Field Day, Info and Register Here

Jan. 24, 25 and 27, Advanced Avalanche Workshop w. Field Day, Info and Register Here

Feb. 9 and 10, Companion Rescue Clinic, Info and Register

COOKE CITY

24 and 25 November, Current Conditions and Avalanche Rescue, 6:30-7:30 p.m. Friday and anytime between 10-2 on Saturday.


Forecasters’ Choice:

The best $30 you’ll ever spend, guaranteed: Our Intro to Avalanches with Field Day. Two evenings of lectures plus a full day in the field digging pits and learning about rescue. Info and Register Here


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