An AVALANCHE WARNING was extended today. Large, natural avalanches were reported as recently as last night. The storm dropped up to 4.5 inches of SWE (over 50 inches of snow) in some locations since Friday onto a weak snowpack. While the storm tapered yesterday afternoon, the snowpack needs time to adjust to this new load. Travel in avalanche terrain and run-out zones is not recommended. The danger is High above 5000 feet today. See Whitefish Range here.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
You are likely to trigger a wind slab today. The colliding air masses over the past three days resulted in variable winds from both the southwest and north over the past few days. Winds were moderate to strong from both directions. So what? This means that wind slabs exist on most aspects above 5000 feet. Wind slabs today 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 avoided smooth, rounded pillows of wind drifted snow today.
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. We all have powder fever, but now is not the time to charge and ski or ride aggressive terrain. Most avalanche accidents occur during or immediately following a storm. So, give the snowpack a few days to adjust to this most recent load. Enjoy this storm snow on low angle terrain that is 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: 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 at least a size 3 (D3) on the destructive scale. It deposited 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.
Sunday: Riders in the South Canyon area of the southern Whitefish Range noted storm slab avalanche activity. Skiers on Skookaleel Ridge in the southern Whitefish Range observed a tender storm slab that easily produced fracturing by stepping on the snow surface. Skiers on Triangle Peak, in the Flathead Range, noted an upside down snowpack, shooting cracks and small windslab avalanche activity.
Storm Totals (2/3/17 to 2/6/17) of SWE (Snow Water Equivalent) and Snow Depth (settled snow total). Settled snow accumulation is likely an underestimation of actual snowfall. For instance, Devil Creek received 39 settled inches and 52 inches of observed interval (12 hour interval) snowfall.
| Station | SWE (inches) | Settled Snow Accumulation (inches) |
| Flattop Mt. SNOTEl (6300 ft.) in Glacier Nat. Park | 4.8 | 27 |
| Stahl Peak (6030 ft.) in northern Whitefish Range | 3.4 | 25 |
| Noisy Basin (6040 ft.) in Swan Range | 3.5 | 41 |
| Big Mt. Summit (6737 ft.) in southern Whitefish Range | 2.1 | 29 |
| Devil Creek (4300 ft.) | N/A | 39 settled (52 inches accumulation) |
Currently, temperatures above 6000 feet range from -12 to 18º F with winds out of the northwest and southwest at 7-18 mph with gusts of 9-27 mph. Today, lingering snow showers should taper mid-morning. Temperatures will rise to the upper teens but remain cooler near the Continental Divide. Winds will be variable across the advisory area but decrease to 5-10 mph with gusts in the 20 mph range.
| 0600 temperature: | -12-18 deg. F. |
| Max. temperature in the last 24 hours: | 15-31 deg. F. |
| Average wind direction during the last 24 hours: | Variable |
| Average wind speed during the last 24 hours: | 5-20 mph |
| Maximum wind gust in the last 24 hours: | 20-35 mph |
| New snowfall in the last 24 hours: | 3-8 inches |
| Total snow depth: | 72-113 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Tapering light snow. Partly/mostly cloudy. | Partly cloudy and cold. | Mostly cloudy and slightly warmer. |
| Temperatures: | 15-25 deg. F. | -4-12 deg. F. | 18-26 deg. F. |
| Wind Direction: | West-Southwest | Southwest-Northwest | West-Southwest |
| Wind Speed: | 4-5 mph | 3-5 mph | 5-8 mph |
| Snowfall: | 0-1 in. | 0 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.
