Recent snow, combined with moderate to strong winds, have formed dangerous avalanche conditions. Above 5000 feet the avalanche danger is CONSIDERABLE with human triggered avalanches likely. Evaluate the snowpack and terrain carefully before committing to any slope. Below 5000 feet the avalanche danger is MODERATE but may rise to CONSIDERABLE if we receive more rain than what is forecast.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Continued moderate to strong southwest winds have created fresh wind slabs on the leeward sides of ridgelines and cross-load mid-slope terrain features. In some locations these slabs were either deposited directly onto a rain crust formed Friday (2/12) or on top of dry cohesionless snow above the rain crust. This rain crust extends to over 7000' in many locations throughout our advisory area and will provide a great sliding surface for these slabs. In isolated areas these fresh wind slabs may sit on top of surface hoar formed last week.
Yesterday's combination of warm air temperatures, wet snow at upper elevations and rain at mid/lower elevations weakened the surface snow. Yesterday evening we saw a brief refreezing of the snow surface before rain and wet snow returned late last night. Above freezing temperatures are expected today at all elevations which, combined with continued rain and/or wet snow, will create a wet avalanche hazard. Today, as the snow surface becomes increasingly moist/wet and pin wheels/rollerballs start to form on steep slopes, you will need to reassess the terrain you are traveling in. Loose, wet avalanches can start small but entrain a substantial amount of snow and do a lot of damage.
In addition to the loose, wet hazard the potential exists to see thin wet slabs forming on top of the recent rain crust. Though they will be thin, they will be more difficult to manage than a wet sluff since they could potentially fracture above you. Keep in mind that even small avalanches can add rapid stress to deeper instabilities and step down.
Buried surface hoar and faceted snow about 1-2.5 feet from the surface exists. In upper elevation locations this has become a hard slab in many locations, and is increasingly more difficult to trigger. However, recent natural avalanches triggered by cornice fall within the past week show this is a low probability/high consequence scenario that should be treated with respect. A couple of these avalanches propagated far and wide (photo 1, photo 2). The additional stress put on these layers with new snow, rain on snow, and wind drifted snow may cause them to become more reactive. These hard slabs are more likely to exist on previously wind loaded slopes. This weak layer is also spotty in distribution making it tricky to identify.
Weak snow surrounding the January 28 and January 17 rain crusts also exists 2-3 feet from the surface. Recent stability tests suggest that these weak layers are gaining strength, but its' still important to dig in the snow and do a stability test. Avoid areas where you are more likely to affect these layers like in shallow snow and in steep, rocky areas.
Cornice formation and failure: Recent new snow with moderate to strong winds have continued to build cornices at upper elevations throughout our advisory area. Above normal air temperatures and wet snow/rain is expected again today which will weaken these features. Today is not the day to ski/ride on or below cornices.
Monday: BNSF Avalanche Safety reported a slab avalanche on Nyack Mountain in the Flathead Range with a crown depth estimated at 3-4 feet deep. Active wind loading was observed at upper elevations. Guy rode into the Canyon Creek drainage of the southern Whitefish Range and observed rollerballs, wet loose avalanche activity and wind loading. In his snowpit he found a decomposing surface hoar layer 14" below the snow surface (observation).
Sunday: Mark was on Sub-Shields in the Flathead Range where wind was actively transporting the new snow and forming thin wind slabs and cornices (video). A seperate party of skiers on Sub-Shields noted about 4 inches of new snow on the rain crust and observed minimal results in stability tests (observation). Skiers in the Marion Lake area also in the Flathead Range found a layer 75 cm from the surface that fractured with hard force in Extended Column Tests and produced clean shears (Q1) in shovel shear tests.
Saturday: We were on Hash Mountain in the Swan Range and found the previous night's snow levels were higher than expected. At 7050 feet there was a rain crust with only 1-2 inches of snow on top. 10-15 mph winds were drifting the snow, there just was not much of it. We found the thin late January crust with weak snow around it 2.5 feet from the surface (photo). This layer did not fracture in our stability tests.
Friday: We were in McGinnis Creek in the southern Whitefish Range and found a wet snow surface up to at least 6000 feet. We noted a layer of decomposing buried surface hoar that was 6-10 inches from the surface that fractured in stability tests (observation).
Thursday: BNSF avalanche safety noted a moist snowpack, warm temperatures, and experienced collapsing on a southeast aspect with a shallow snowpack (observation). They also observed a cornice triggered slab avalanche on Mt. Cameahwait in the Flathead Range (photo), but are uncertain of the date of occurrence. Glacier Park rangers observed recent wet avalanche activity on the south aspects of Mt. Stanton yesterday (observation). Snowmobilers in Canyon Creek in the southern Whitefish Range also observed recent loose, wet avalanches (photo).
Visit our Observations page and our You Tube channel for more observations from the entire season.
Thanks to everyone for submitting observations. They are extremely useful and could help save lives.
HOW TO SUBMIT OBSERVATIONS:
Email: [email protected]
Call and leave a message: 406.387.3821
You can also submit quick observations via text: 406.241.4571 (FAC mobile)
OR
Submit Snowpack Observations: http://www.flatheadavalanche.org/node/add/snowobs
Submit Avalanche Observations: http://www.flatheadavalanche.org/node/add/avyobs
After a break from precipitation during the day yesterday rain and high elevation snow returned to our area late last night. In the past 24 hours we have picked up approximately 0.5 inches of snow water equivalent and up to 5 inches of snow. Winds were out of the southwest at 10-20 mph with gusts from 16-58 mph. As of 6:00 am, temperatures above 6000 feet range from 28º-34º F, and winds continue to blow out of the southwest at 10-27 mph with gusts from 16-39 mph. Today we should see continued rain/snow showers with snow levels rising to 5500 feet. Winds will continue out of the west and southwest at 15-30 mph with gusts in the 40s.
| 0600 temperature: | 28-34 deg. F. |
| Max. temperature in the last 24 hours: | 29-36 deg. F. |
| Average wind direction during the last 24 hours: | SW |
| Average wind speed during the last 24 hours: | 10-20 mph |
| Maximum wind gust in the last 24 hours: | 12-57 mph |
| New snowfall in the last 24 hours: | 0-5 inches |
| Total snow depth: | 72-89 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Continued rain/snow with rising snow levels. | Light precipitation. | A few light showers. |
| Temperatures: | 40-48 deg. F. | 26-33 deg. F. | 38-45 deg. F. |
| Wind Direction: | W-SW | SW | S |
| Wind Speed: | 14-19 gusts 39 | 5-11 gusts 29 | 5-6 |
| Snowfall: | 0-2 in. | 0-1 in. | 0 in. |
| Snow Line: |
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
