19-20

GNFAC Avalanche Forecast for Wed Feb 26, 2020

Snowpack and Avalanche Discussion

<p>In the mountains around Bozeman and Big Sky wind-loading is the primary concern. By yesterday morning snowfall totaled 8-12” around Big Sky and 15-20” in the Bridger Range and Hyalite. This snow bonded well to the old snow surface. Dave and I toured north of Bridger Bowl and dug on south, east and northerly aspects and did not find instabilities with the new snow (<strong><a href="https://youtu.be/Vodj5XGXV0o">video</a></strong&gt;). Westerly wind picked up yesterday afternoon at many elevations, not just at the ridgetop. This morning drifts at ridgelines and in gullies will be plentiful and ripe to avalanche. Shooting cracks is the #1 sign wind slabs will avalanche, so stay clear of drifted snow and stick to sheltered slopes that still hold powder.</p>

<p>The snowpack has an underlying weakness of sugary facets at the ground that could break from the weight of the recent snowfall, especially on slopes wind-loaded. Dave had a surprisingly poor stability test on this layer in Beehive Basin on Monday (<strong><a href="https://youtu.be/xNT0eYKpuoY">video</a></strong&gt;). This layer is not producing widespread instability, but it is in the back of our minds since avalanches failing on it would be large.</p>

<p>For today, triggering avalanches on wind-loaded slopes is likely and the danger is rated CONSIDERABLE. All other slopes have a MODERATE danger.</p>

<p>Ian was in Cooke City the last two days and found generally stable conditions, except on slopes that have been recently wind-loaded (<strong><a href="https://youtu.be/9g-x7o56ek8">video</a></strong&gt;). Yesterday’s wind created drifts that were easy triggered (<strong><a href="https://www.mtavalanche.com/images/20/small-natural-wind-slabs-crown-bu…;, <a href="https://www.mtavalanche.com/images/20/snowmobile-triggered-wind-slab-ne…;) and will remain sensitive today. On slopes without drifts he found stable conditions. We are always thinking about the sugary, weak snow at the ground, but it is dormant for now and triggering a slide on this layer is unlikely until the mountains get a large storm. For today, the avalanche danger is rated MODERATE on all wind-loaded slopes and LOW everywhere else. Wind-loaded slopes should be avoided. Recent avalanches or shooting cracks are signs to stay clear of wind-drifted terrain.</p>

<p>The southern mountains to West Yellowstone and Lionhead have not gotten snow lately, only wind. Wind drifts will be minimal and not easy to trigger. The snowpack in these mountains is conditionally stable. This may change with future snowfall, but today things are quiet and avalanches are unlikely. The danger is rated LOW on all slopes.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></strong></u>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.

COOKE CITY

Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.

BOZEMAN

Small natural and snowmobile triggered windslabs near Cooke City

COOKE CITY
Cooke City
Code
SS-AM-R1-D1
Latitude
45.02020
Longitude
-109.93800
Notes

Observed two small natural wind slab avalanches on the morning of 2/25 near Daisy Pass.

Then saw four small snowmobile triggered slides on windloaded slopes near Goose Lake that were triggered today. These slides broke 1-2' deep on small slopes. 

Number of slides
4
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
R size
1
D size
1
Slab Thickness
12.0 inches
Vertical Fall
40ft
Slab Width
40.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Tue Feb 25, 2020

Snowpack and Avalanche Discussion

<p>Dangerous avalanche conditions exist with 15-20” of new snow in the Northern Gallatin and Bridger Ranges (1.3” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> - SWE) and 5-10” in the Northern Madison Range (0.6” of SWE). Yesterday in Hyalite Canyon Doug noted that it was snowing and blowing hard, actively loading slopes at all elevations and quickly forming drifts that he carefully avoided. At the same time, I was touring in Beehive Basin and found new snow and the weak snowpack structure we have seen all year (<a href="https://www.youtube.com/watch?v=xNT0eYKpuoY"><strong>video</strong></a&…;). This winter’s snowpack has repeatedly demonstrated that snowfall and heavy wind loading leads to large avalanches failing on deeply buried weak layers. You can go to our <strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log">Weather and Avalanche Log</a></strong> to see this pattern.</p>

<p>Today, smaller avalanches are likely in many areas and there is a scary possibility of large avalanches especially on heavily wind loaded slopes like Saddle Peak. Use cautious route-finding to avoid high consequence avalanche terrain today. Human triggered avalanches are likely and the danger is rated CONSIDERABLE.</p>

<p>The mountains around Cooke City received 3-5” of new snow in the last 36 hours (0.4” of SWE) with strong wind gusts near ridgelines. Ian skied in the Republic Creek drainage yesterday and observed fresh drifts and some shooting cracks within the top 6” of the snow. Recently, the snowpack in Cooke City has been handling new snow loads well and avalanches are staying contained within the upper layers of the snowpack. However, the presence of deeply buried weak layers still gives us pause.</p>

<p>Today, avoid steep slopes with fresh drifts especially in high consequence terrain such as gullies, in the trees, and above cliffs. Larger, deep slab avalanches are unlikely as weak snow near the ground gets harder to trigger but remain vigilant to this lessening possibility by following safe travel protocols and looking for any sign of deeper instabilities. Human triggered avalanches are possible and the avalanche danger is MODERATE.</p>

<p>The Southern Madison and Gallatin Ranges and Lionhead area received 0-1” of snow in the last 36 hours. This fell on a strengthening snowpack and will not change the avalanche danger. Yesterday, winds gusted up to 40 mph from the north, but without much new snow available for transport wind loading will only be a factor in isolated areas. Watch Ian and Doug’s <strong><a href="https://www.youtube.com/watch?v=2IzNvRo0R3w">video</a></strong&gt; from Skyline Ridge to learn more about the current state of the snowpack.</p>

<p>Avoid the isolated slopes where you find fresh drifting especially in higher consequence terrain. Human triggered avalanches are unlikely and the avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank"><strong>observation form</strong></a>, email us (<a href="mailto:mtavalanche@gmail.com&quot; target="_blank"><strong>mtavalanche@gmail.com</strong></a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.

COOKE CITY

Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.

BOZEMAN