Cornices and glide cracks have the potential to fail and trigger wind slabs at upper elevations. Give both cornices and slopes with glide cracks a wide berth today. As snow accumulates today fresh wind slabs may form on top of widespread crusts. Weak snow near a series of crusts exists in the upper snowpack that should be assessed before committing to a slope. The avalanche danger is MODERATE above 6000 feet.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Recent observations report both natural and human triggered cornice fall. We observed some impressive cornices across the area. The huge amount of stress a falling cornice puts on the snowpack can trigger deeper weak layers like wind slabs or weak snow around the late February crust. Skiers near Mt. Grant observed cornice fall and subsequent slab avalanches Saturday. Skiers in the Avalanche Lake area reported massive amounts of cornice blocks that had fallen over the past week. Cornices can release farther behind the ridgeline than expected so it is important to keep a safe distance when traveling above them and limit your exposure time when traveling below.
As we progress into a spring snowpack glide crack formation and failure will become more prevalent. A recent glide crack avalanche was reported in the Flathead Range over the weekend (image). Due to their unpredictable nature it is best to avoid all slopes with glide cracks on them.
Old wind slabs can be found at upper elevation locations of our area. It is generally taking a large force (like a cornice) to trigger these slabs, but skiers in the Flathead Range reported recent wind slab avalanches triggered by both cornice fall and glide crack failure (image, image). The close call on Peak 6996 also involved cornice failure triggering a wind slab. As the day progresses and forecasted snow accumulates fresh, thin wind slabs will form on leeward aspects at upper elevations. With north and east winds expected today be aware of atypical loading patterns. These slabs will form on a crust on most aspect and may become reactive.
Additional concerns: Although we have not received any reports of avalanches failing on weak layers deeper in the snowpack we cannot write these layers off just yet. This weak snow surrounds a series of crusts that are 1.5 to 3 feet from the surface. Digging into the snow and performing stability tests is the only way to determine if this weak layer exists. Stability tests in some locations show they still have the potential to break across a slope (video1, video2). Where you find weak, faceted snow around these crusts it is important to choose appropriate terrain as it is possible to trigger an avalalanche. Put the odds in your favor by avoiding steep, convex roll-overs, and rocky terrain where the snowpack is notoriously shallow.
Monday: I traveled to the Canyon Creek area of the southern Whitefish Range where produced numerous pinwheels/rollerballs and small wet loose slides on top of a rain crust. We also observed several glide cracks on south facing terrain which had initially formed several weeks ago (observation).
Sunday: Skiers in the Avalanche Lake drainage of Glacier Park reported sizable wet loose activity from Saturday and also observed sizable wet loose slides during their tour (observation). Multiple parties of skiers in the Whitefish Range and the Flathead Range reported wet, loose avalanches up to size D2 (observations).
Saturday: Skiers in the Mount Grant vicinity in the Flathead Range reported wind slab, glide, and wet loose, natural avalanches that occurred yesterday (observation). A glide crack failed on smooth rock slabs that triggered a shallower slab (image). Another party of skiers in the Skiumah Drainage observed natural avalanche activity on north and northwest aspects on Mt. Penrose. Skiers on Elk Mountain in southern Glacier Park observed strong wind transporting snow along high ridgelines.
Friday: A skier on Peak 6996 near Marias Pass in the Flathead Range unintentionally broke two large blocks of cornice and was subsequently caught in a small soft slab avalanche. The cornice triggered an avalanche that propagated 40-60 feet across the slope and ran about 400 feet. The skier was caught and reported that he "got a little beat up" (observation).
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
Seasonal temperatures returned to our area yesterday with most upper elevation stations reporting max temps in the mid 30s to low 40s. Currently, mountain temperatures are 22º-36º F with winds out of the north-northeast at 4-16 mph with gusts from 14-27 mph. Snow showers with seasonal temperatures are on tap for today with the Flathead Range and Swan Range favored for precipitation. .
| 0600 temperature: | 22-36 deg. F. |
| Max. temperature in the last 24 hours: | 32-42 deg. F. |
| Average wind direction during the last 24 hours: | SW |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 23-36 mph |
| New snowfall in the last 24 hours: | 0-1 inches |
| Total snow depth: | 79-105 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Snow developing | Light snow showers | Light snow showers |
| Temperatures: | 33-44 deg. F. | 23-30 deg. F. | 34-45 deg. F. |
| Wind Direction: | E-SE | SW | W-SW |
| Wind Speed: | 4-5 | 3 | 9-10 gusts 20-24 |
| Snowfall: | 1-5 in. | 1-2 in. | 1-2 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.
