The widespread natural avalanche cycle has slowed, but human triggered avalanches are still likely and natural avalanches are possible. The storm ended Monday and the new snow has had a little time to strengthen, but it still sits on a weak snowpack and instabilities associated with the storm are lingering. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. The danger is CONSIDERABLE at all elevations today.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
You are likely to trigger a wind slab today. Winds quieted yesterday, but previous loading from strong and variable winds spread snow around all aspects at mid and upper elevations. Wind slabs could be up to 5 feet thick and are likely to exist on all aspects, and could be found mid-path as well as just below ridges. Look for and avoid smooth, rounded pillows of wind drifted snow.
Observers are still reporting human triggered and natural avalanches occurring within the storm snow at all elevations. Time should help but instability associated with the storm slab is lingering.
Temperatures increased on Sunday during the storm before dropping again. This produced a heavier layer on top of a softer, lighter layer (an upside down snow structure) within the storm snow that could still be sensitive to human triggers today. This storm snow also fell onto a variety of weak layers and crusts, including the Jan. 19 crust and facets surrounding, buried surface hoar, and near surface facets. Take time to dig into the snow, perform stability tests, and learn what's under your machine or feet.
The huge amount of new snow also fell onto a weak snowpack structure consisting of near surface weak layers and crusts as well as weak snow (facets) near the ground in some locations. An avalanche that initiates at the snowpack surface may step down to a deeper weak layer producing a much larger slide. Cracking in the snow surface is an obvious sign of storm slabs. Also, watch for loose, dry avalanches (sluffs) on steep slopes involving the new storm snow that could carry you into a terrain trap and bury you.
While the storm has ended, dangerous avalanche conditions still exist. Observers are still finding facets and buried surface hoar above the January 19 ice crust. This layer now has two to three feet of snow above it. Now is still not the time to ski or ride aggressive terrain. Enjoy this storm snow on low angle slopes that are not connected to avalanche terrain.
An avalanche incident occurred Saturday in the Lost Johnny area of the Swan Range. Two members of a snowmobile party were caught in an avalanche with one partial burial and one full burial. Fortunately no one was hurt (observation).
Tuesday: Seth ventured to Skookaleel Ridge in the Southern Whitefish Range and observed previous natural avalanche activity of small size and sensitive wind slabs on top of the January 19 crust. A public observation from the Central Apgar Range reported failure and propagation with moderate force in stability tests. Early Tuesday morning a large and destructive natural avalanche was reported by BNSF Avalanche Safety in the Wahoo drainage in the Flathead Range. The avalanche was estimated as a size 3 (D3) on the destructive scale. It left a debris pile about 50 yards wide and 5 feet deep on the railroad tracks.
Monday: BNSF Avalanche Safety reported 14 observed natural avalanches (11 of which reached the railway). Whitefish Mountain Resort Ski Patrol reported 6-12 inch storm slabs and wind slabs that released 12-24 inches deep. Guy and Erich joined Ski Patrol for control routes and also observed 5 natural avalanches just outside the ski area boundary on west aspects (near Ghoulie Point) visible from East Rim.
See below for all observations this season.
Currently, temperatures above 6000 feet range from 9 to 16º F with winds out of the northwest and southwest at 5-19 mph with gusts of 4-24 mph. Today should be mostly dry with temperatures rising to the upper teens and twenties. Winds will be light to moderate cross the advisory area from the West/Southwest at 6-10 and with gusts to 25 near the Continental Divide.
| 0600 temperature: | 9 to 16 deg. F. |
| Max. temperature in the last 24 hours: | 16 to 30 deg. F. |
| Average wind direction during the last 24 hours: | Variable |
| Average wind speed during the last 24 hours: | 1 to 19 mph |
| Maximum wind gust in the last 24 hours: | 13 to 29 mph |
| New snowfall in the last 24 hours: | 0 inches |
| Total snow depth: | 71-112 inches |
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Cloud Cover: | Partly/mostly cloudy. | Partly cloudy with increasing winds and snow. | Warm with strong South winds, snow and rain. |
| Temperatures: | 18-26 deg. F. | 13-22 deg. F. | 33-41 deg. F. |
| Wind Direction: | West-Southwest | South-Southwest | South-Southwest |
| Wind Speed: | 6-7 mph | 7-8 mph with Gusts to 21 mph | 12-22 mph with Gusts to 49 mph |
| Snowfall: | 0-1 in. | 3-6 in. | 5-12 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.
