19-20

Skier triggered avalanches in the new snow in Middle Basin

Middle Basin
Northern Madison
Code
SS-ASc-R1-D1.5-I
Elevation
9300
Aspect
W
Latitude
45.33840
Longitude
-111.37700
Notes

My partner and I toured over from Beehive into Middle Basin today (saw your car in the parking lot) and finding relatively dry snow in the shade headed for a west facing chute on the ridge that divides Middle and Bear Basins. The chutes walls kept it mostly shaded all morning and it was mostly cloudy as we started skinning up its apron. We had no cracking or signs of cohesion as we approached and a relatively easy boot pack up the chute. A couple of hand pits on the way up showed little cohesion within the top layer and a fairly dry snowpack underneath. We made plans for sluff management with protected spots to let it pass on both sides of the chute. While stomping out a platform we were able to kick off boot sized chunks of snow with no reaction My partner dropped first and his first turn kicked off a storm slab a couple of inches thick from his skis a few feet to his right against the wall of the chute. After a jump turn into a ski cut to one of those protected spots, he triggered a larger storm slab about 4” thick that propagated from the edge of our boot pack on one wall of the chute to the other wall about 20/30’ across and then ran the rest of the chute onto the apron about 300’ below us. No one was caught or injured. We skied out of the chute on the crust bed surface and spent the rest of the day enjoying some low angle trees. The chute was around 40° at 9,000’-9,500’ and west facing. We also noted a point release on an east aspect at about 9,300’ off the ridge separating Beehive and Middle Basin. It looked like a block of snow fell from a south facing cliff onto the slope below. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
1
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness
4.0 inches
Vertical Fall
300ft
Slab Width
25.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

After a jump turn into a ski cut to one of those protected spots, my partner triggered a storm slab about 4” thick that propagated from the edge of our boot pack on one wall of the chute to the other wall about 20/30’ across and then ran the rest of the chute onto the apron about 300’ below us. No one was caught or injured. We skied out of the chute on the crust bed surface and spent the rest of the day enjoying some low angle trees. The chute was around 40° at 9,000’-9,500’ and west facing. Photo: C. Oshiro-Leavitt

Northern Madison, 2020-03-09

After a jump turn into a ski cut to one of those protected spots, my partner triggered a storm slab about 4” thick that propagated from the edge of our boot pack on one wall of the chute to the other wall about 20/30’ across and then ran the rest of the chute onto the apron about 300’ below us. No one was caught or injured. We skied out of the chute on the crust bed surface and spent the rest of the day enjoying some low angle trees. The chute was around 40° at 9,000’-9,500’ and west facing. Photo: C. Oshiro-Leavitt

Northern Madison, 2020-03-09

Natural Wet, Loose Avalanches Hyalite

Hyalite - main fork
Northern Gallatin
Code
WL-N-R1-D1-I
Latitude
45.44720
Longitude
-110.96200
Notes

Today in Hyalite there was roughly 5" new snow. It quickly lost cohesion when the sun came out and many size 1 dry and wet loose came off of steep rocky areas. I did not observe anything larger. Yesterday I observed a cornice fall on an E aspect of Mt. Bole around 9500 ft that probably occurred on 3/6. It ran several hundred meters downhill, entrained some surface snow, and appeared to trigger a size 2 slab when it encountered steeper terrain. That being said I was at G1 so I didn't really get a good look at it.

Number caught
0
Number buried
0
Avalanche Type
Wet loose-snow avalanche
Trigger
Natural trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Slab Thickness
5.0 inches
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Skier triggered avalanches in the new snow on Saddle Peak

Saddle Peak
Bridger Range
Code
SS-AS-R2-D2-I
Elevation
9000
Aspect
E
Latitude
45.79320
Longitude
-110.93500
Notes

Multiple laps on Saddle today. New snow peeling cleanly on hard crust on ski cuts at steep roll overs. Would run until pitch tapered off. Ran slow but pretty big. Debris was 4-6 feet deep. South Central (upper face) of South Saddle and Face of North Saddle under 2nd rock were the biggest producers.

Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
2
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness
8.0 inches
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Natural Dry, Loose Avalanches on Blackmore

Mt Blackmore
Northern Gallatin
Code
L-N-R1-D1-I
Elevation
9800
Aspect
E
Latitude
45.44450
Longitude
-111.00200
Notes

Dry loose avalanches on Blackmore. The snow stayed surprisingly cold and dry throughout the day.

Number of slides
4
Number caught
0
Number buried
0
Avalanche Type
Loose-snow avalanche
Trigger
Natural trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Sun Mar 8, 2020

Snowpack and Avalanche Discussion

<p>I was happy to see temperatures cold enough to make snow instead of rain. Four to seven inches of snow is measuring about .5” of snow water equivalent—enough to improve the skiing and riding conditions yet not enough of a load to increase the <u>dry snow</u> instability. Conditions will change rapidly today when sunshine and above freezing temperatures moisten the new snow and trigger wet avalanches. These slides will be confined to slopes getting sunshine. Yesterday, small wet avalanches were seen around Cooke City (<strong><a href="https://www.mtavalanche.com/images/20/natural-wet-loose-avalanche-cooke…;) and skiers triggered a slab avalanche (likely wet) in Hyalite on an 8700’ east-facing slope to the north of Mt. Blackmore. They kicked off a cornice which broke 150’ wide in the old snow and ran 1,000’ downslope (<strong><a href="https://www.mtavalanche.com/node/22360">photo, video and details</a></strong>). Ian was nearby on Mt. Ellis and found wet snow to the ground on a similar aspect and elevation (<strong><a href="https://youtu.be/H5030DBBQhQ">video</a></strong&gt;). Although colder weather prevails in the next few days, deeply buried wet snow will not refreeze quickly.</p>

<p>Wet avalanches are a function of water melting bonds and weakening the snowpack structure. Dry avalanches are a function of slopes getting a critical load that breaks a weak layer. We load slopes by skiing and riding on them, from snowfall and from cornices falling. Right now cornices are huge and easy to break. There is weak, sugary snow at the bottom of the snowpack in all our ranges and a cornice fall could trigger an avalanche on this layer. Give these overhangs of snow a wide berth if you travel along a ridge and avoid being underneath them.</p>

<p>If you step off your skis and sink to the ground in wet snow, like Ian did yesterday, then you should back off your objective. This is a sign the snowpack has lost strength. Wet snowpacks are unpredictable and could avalanche as the skiers in Hyalite discovered. If the snow is dry, then slopes will be generally stable. For today the <u>dry snow</u> avalanche danger is rated LOW. However, the <u>wet snow</u> avalanche danger will increase to MODERATE on slopes getting direct sunshine.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an <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

March 13 and 14, Friday and Saturday, (last of the season) 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