The avalanche danger is MODERATE above 6000 feet on wind loaded terrain steeper than 35º. Recent winds drifted snow onto a variety of surfaces like surface hoar and sun crusts that can cause instability to linger. Human triggered avalanches are possible today. Carefully evaluate the snowpack before committing to any slope, particularly in steep, wind loaded terrain. The avalanche danger is LOW on all other terrain.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Continued southwest flow has brought light winds with moderate to strong gusts at upper elevations throughout our advisory area. These winds have been strong enough to transport snow but observations of a reactive wind slab have been few and far between. However, don't let the recent lack of avalanche activity lull you into complacency. Some areas have seen slabs formed on top of a variety of weak snow surfaces such as surface hoar and near surface facets. Leeward and cross loaded sunny aspects (southeast and east) have developed a sun crust that snow is drifting on. It remains important to carefully assess windloaded areas before committing to a slope. Wind slabs are likely to be thicker in areas near the Continental Divide where wind speeds have been stronger. Look for smooth, rounded features on the slope especially on steep convex rollovers, on leeward sides of ridges and cross-loaded gullies.
New storm snow depositing on near surface weak layers and slippery sun crusts. With snow finally back in the forecast, we need to be aware that it may be falling on weak layers and/or sun crusts that were formed during our recent dry spell. Surface hoar and near surface facets (small, weak snow grains just under the snow surface) exist throughout the advisory area. Recent snowfall buried these weak layers, but they should not become an "out of sight, out of mind" issue. It is important to monitor the reactivity of these weak layers as new storm snow continues to accumulate on top of them. On sunny aspects, a sun crust formed that could become a potential bed surface as more snow falls as well.
As you dig deep into the snowpack you will encounter the remnants of the December 9 rain crust. Currently it is located about 2/3 below the snow surface. This crust/ice mass is a good landmark to monitor as the season progresses.
Sunday, skiers in the Middle Fork noted "lots of wind" that was transporting snow in the upper elevations but they noted that this newly drifted snow was not reactive.
On Saturday, Guy and I traveled to Baldhead Mountain in the Flathead Range. We found soft, cohesionless wind drifted snow on leeward aspects and buried surface hoar 2-4 inches deep (photo). We also noted weak snow near the ground that was unreactive in stability tests (observation).
Also on Saturday, skiers in the Marion Lake area, also in the Flathead Range found a shallow snowpack (about 3 feet deep). On sunny aspects they found a 1 inch crust with 2 inches of recent snow on top. Below the crust they noted weak snow that failed and propagated in stability tests.
Friday, Erich and Todd traveled up a ridge that divides the Lost Johnny and Wounded Buck drainages in the Swan Range. They observed buried surface hoar and near surface facets in the top 2-3 inches of snow. The snowpack in this area was deep and uniform (photo, video).
Thursday, Erich went on the hunt in the southern Whitefish Range for recently buried surface hoar, and was successful. He found it about 2 inches below the surface. See observation and video for details. Skiers in the Paola Creek drainage in the Flathead Range noted wind transport near ridgetops and developing wind slabs in exposed areas (observation).
On Wednesday, skiers in the Marion Lake area observed a wind slab in a cross-loaded gully on nearby Mt. Adams that appeared to be 1-2 days old, around 150 feet wide and up to 1 foot deep (photo). Also on Wednesday, on Sub-Shields in southern Glacier National Park, GNP rangers observed surface hoar (though melting on southerly aspects) and a snowpack that has settled considerably since last week. That same day nearby on Snowslip and Running Rabbit Mountains, skiers observed unreactive wind slabs, plenty of surface hoar, and a decomposing December 9 rain crust near the ground (observation).
Thanks to everyone for submitting observations. They are extremely useful for everyone.
Visit our Observations page and our You Tube channel for more observations from the entire season.
Please let us know what you are seeing out there. Your observations are important and valued.
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
Light southwest winds with moderate to strong gusts continued yesterday and overnight. Currently, we have light snow showers, mountain temperatures have warmed and range from 18º-24º F with winds out of the southwest at 4-15 mph and gusts up to 20 mph. Today, expect light snow to continue with the Swan Range favored, temperatures in the upper 20s to low 30s and winds to continue out of the southwest at 15-20 mph with gusts up to 40 mph in upper-elevations. Tonight a warm moist system enters our area bringing a much needed shot of moisture along with rising freezing levels and breezy conditions.
| 0600 temperature: | 18-26 deg. F. |
| Max. temperature in the last 24 hours: | 18-26 deg. F. |
| Average wind direction during the last 24 hours: | SW |
| Average wind speed during the last 24 hours: | 5-20 mph |
| Maximum wind gust in the last 24 hours: | 10-36 mph |
| New snowfall in the last 24 hours: | 0 inches |
| Total snow depth: | 45-60 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Light snow with the Swan Range favored. | Warm moist system enters our area. | Snow with moderate to strong winds and rising freezing levels. |
| Temperatures: | 26-34 deg. F. | 19-27 deg. F. | 29-38 deg. F. |
| Wind Direction: | SW | SW | SW |
| Wind Speed: | 9-14 gusts 32 | 9-11 gusts 36 | 11-16 gusts 31 |
| Snowfall: | 1-5 in. | 1 in. | 2-5 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.
