Impressively windy conditions, combined with new snow, formed wind slabs earlier this week. New snow overnight and throughout today, combined with northeasterly winds, will form thin wind slabs on atypical slopes. The avalanche danger is MODERATE above 5000 feet. Human triggered avalanches are possible today, particularly on wind loaded slopes. Carefully evaluate all wind loaded terrain before committing to a slope.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Earlier this week, moderate to strong winds combined with new relatively dense snow, formed wind slabs at mid and upper elevations. In many places these slabs were deposited on top of lower density snow raising a red flag for backcountry users. These slabs have had a bit of time to stabilize but due to the weak layer they were deposited on they should still be approached with caution. New snow yesterday and throughout today, coupled with east-northeasterly winds, will form new thin wind slabs on atypical slopes. In this case atypical meaning southeast, south, southwest and west. These slabs may be deposited onto previously scoured or wind buffed surfaces. In other cases they will be deposited onto a thin layer of new snow. BNSF Avalanche Safety reported an audible collapse (whumph) in a wind slab Thursday which is an obvious sign of instability. In isolated areas you may even encounter a few hard slabs. They will be supportable, feel hollow, and "drummy" and should be avoided. Pay attention to signs of instability like cracking and collapsing in the snowpack.
As the storm snow from early in the week settles into a more cohesive slab it is important to continue to evaluate the recent snow and old snow interface. It is important to assess the upper snowpack for potential weak layers like surface hoar and weak, faceted snow that formed during the dry, cold period last week. Look for this weak interface 1-2 feet from the surface and pay attention to obvious signs of instability. Also, in some locations, like John F. Stevens Canyon and approaching the Divide you may find weak (faceted) snow around crusts 1.5-3.5 feet from the surface (video). The most common places to trigger these deeper slides are in steep, rocky terrain, and areas with a relatively shallow snowpack.
Join us at the Kalispell Brewing Company on Tuesday, December 27th to support a great cause by drinking delicious, locally-made beer. Kalispell Brewing will donate $1.00 per every beer sold to Friends of Flathead Avalanche Center (FOFAC) between 5:00 and 8:00 p.m. See you at the brewery!
Friday: Guy traveled to Snowshed Mountain in the Flathead Range where he found entire slopes either scoured or wind loaded above 6800'. In his pit he found a variety of wind slabs and one thin faceted layer which was not reactive in his tests. Zack was in Noisy Basin in the Swan Range where he noted wind affected snow above 5000' and a thin breakable wind crust above 6000' on ridges and open slopes. His layer of concern was the weak snow at the old snow/new snow interface. Mark traveled to Peak 6996 in southern Glacier Park where he found a sun crust on steep low elevation southerly aspects and wind affected snow at all elevations. At mid elevations the newly formed wind slab sat on top of low density snow. In an upper elevation pit the basal layer consisted of weak faceted snow that sandwiched an ice mass.
BNSF Avalanche Safety was in the John F. Stevens Canyon Thursday and found variable conditions both on the surface and snowpack structure. They noted one audible collapse in the snowpack associated with recent windslab (observation). Whitefish Mountain Resort Ski Patrol reported minimal results using explosives for avalanche control.
Wednesday, we were in Canyon Creek in the southern Whitefish Range. There was wide-spread avalanche activity that occurred on Tuesday. Many of the crowns were difficult to see at first glance because they were mostly filled in by snow and wind blown snow. However, we could see remnants of crowns on Skookoleel Ridge and several on the ridgeline to Ghoulies Point. These avalanches ranged in depth from 12 to 18 inches and failed on the old pre-storm surface. Other skiers were in the same area and noted a more dense layer overlying the lighter old snow.
Light snow moved into our area mid day yesterday and continued overnight depositing 1-7" across our region. A weak arctic air mass also began moving into our area bringing with it east-northeast winds to most locations this morning. Currently, mountain temperatures range from 19-28º F, and winds are out of the east-northeast at 4-5 mph with gusts from 5-6 mph. Today, temperatures will not rise much above this mornings readings. Winds will generally be light with occasional moderate gusts. Light snowfall continues tonight with cold temperatures.
| 0600 temperature: | 19-28 deg. F. |
| Max. temperature in the last 24 hours: | 20-31 deg. F. |
| Average wind direction during the last 24 hours: | W/SW |
| Average wind speed during the last 24 hours: | 2-7 mph |
| Maximum wind gust in the last 24 hours: | 11-14 mph |
| New snowfall in the last 24 hours: | 1-7 inches |
| Total snow depth: | 45-65 inches |
| Saturday | Saturday Night | Sunday | |
|---|---|---|---|
| Cloud Cover: | Light snow developing with easterly winds. | Snow tapering with continued northeasterly light winds. | Cooler temperatures and dry with light northeasterly winds. |
| Temperatures: | 19-28 deg. F. | 1-9 deg. F. | 10-18 deg. F. |
| Wind Direction: | East-Northeast | Northeast | North |
| Wind Speed: | 7 mph with gusts to 23 | 12 mph with gusts to 28 | 5-6 mph with gusts to 17 |
| Snowfall: | 1-4 in. | 1-3 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.
