Periods of heavy snowfall with relatively warm temperatures overnight combined with increased wind speeds created dangerous avalanche conditions. Human triggered avalanches are likely, particularly in wind loaded terrain. The avalanche danger is CONSIDERABLE above 5000 feet. Cautious route-finding and conservative decision making are essential today.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
Another shot of snow and increasing winds thickened recently formed wind slabs. In some areas they may be 3-4 feet thick along exposed ridgelines. Additionally, winds funneling through canyons cross-loaded mid-slope terrain features so you're not necessarily out of the woods once you drop below the ridges. A skier triggered avalanche yesterday in Skook Chutes in the southern Whitefish Range is thought to have occured in previously cross-loaded terrain (observation). In isolated areas, reports of prolonged periods of graupel during the recent storm will increase instability of recent slabs formed on this layer. Wind loaded terrain is easily identified and should be avoided today. Look for smooth, rounded features on the snow surface. Watch for obvious signs of instability like cracking and collapsing while traveling along ridgelines and riding over low consequence wind loaded features.
Most of the snow across the area came in rapidly in the early morning hours. Given the relatively warm temperatures during the snowfall we could see a sensitive, upside-down storm layer. Watch for obvious signs of instability like recent avalanche activity, collapsing of the snowpack (whumfing), and cracking in the snow surface. Choose low angle terrain to play in while giving the new snow a chance to settle. Loose snow avalanches involving storm snow are also a possibility and can entrain a substantial amount of snow. If you're caught off guard a sluff can be consequential in terrain traps like narrow gullies, treed areas, and cliffs.
In most locations across the advisory area there is weak snow buried in the snowpack. These layers include: weak(faceted) snow formed during the cold period in mid-December, weak snow surrounding an early December rain crust, and we continue to find weak snow near the ground primarily in areas with a shallow snowpack. Though these layers of weak snow have been widely dormant it is extremely important to not let your guard down. I consider these layers ticking time-bombs. There is a lot of uncertainty around how much of a load they can handle before they become a problem and the transition can occur rapidly. The most common places to trigger these deeper slides are in steep, rocky terrain, and areas with a relatively shallow snowpack.
Yesterday we received a report of a skier triggered avalanche in the Skook Chutes in the southern Whitefish Range. The skier was reported as being partially buried but sustained no injuries. We will provide more information when it is available. Erich was around Snowslip Mountain in the Lewis Range in southern Glacier National Park and intentionally triggered a very small wind slab avalanche from a safe location above the ridge.
Skiers in the Essex Mountain area in the Flathead Range on Wednesday noted obvious signs of instability like collapsing (whumfing) in recently wind loaded terrain. they also observed cross-loaded slopes in the upper elevations. Another party nearby did not observe any obvious red flags but noted an upside down snow pack near the ridgeline.
Tuesday: BNSF Avalanche Safety reported avalanche debris at about 4800 feet in John F. Stevens Canyon in southern Glacier Park. Visibility was poor and they could not see the starting zone. Skiers in Pinnacle Creek in the Flathead Range reported poor stability involving the new storm snow in stability tests as well as cracking of this new surface snow. They also reported fracturing and propagation on a layer of weak facets near the bottom of a shallow snowpack.
See below for all observations this season.
Overnight we picked up 5-7 inches of snow, with snow water equivalents from 0.6-0.9 inches. Winds over the last 24 hours were 5-15 mph out of the southwest with gusts from 35-45 mph. Currently, Temperatures above 6000 feet range from 19º-24º F, and southwest winds are 12-18 mph with gusts in the 30s and 40s. Today we should see mostly cloudy skies with a few lingering showers becoming partly cloudy.
| 0600 temperature: | 19-24 deg. F. |
| Max. temperature in the last 24 hours: | 21-27 deg. F. |
| Average wind direction during the last 24 hours: | WSW |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 25-45 mph |
| New snowfall in the last 24 hours: | 5-7 inches |
| Total snow depth: | 55-80 inches |
| Friday | Friday Night | Saturday | |
|---|---|---|---|
| Cloud Cover: | Mostly cloudy with light snow showers. | Light snow showers. | Partly cloudy and cooler. |
| Temperatures: | 24-35 deg. F. | 9-16 deg. F. | 16-24 deg. F. |
| Wind Direction: | West | West | Southwest |
| Wind Speed: | 10-12 gusts 29-36 | 7-9 gusts 20-24 | 9-13 gusts 20-33 |
| Snowfall: | 0-3 in. | 0-4 in. | 0-3 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.
