Over the past week wind slabs have formed on a variety of aspects at upper elevation locations. Most of these have had time to strengthen but isolated pockets of instability may still exist, particularly in the alpine terrain. The avalanche danger is MODERATE on wind loaded terrain above 6000 feet where human triggered avalanches are possible. Carefully evaluate all wind loaded terrain before committing to a slope.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
Several generations of wind slabs exist on all aspects at upper elevation locations, particularly in the alpine terrain. Most of these have had time to strengthen and obvious signs of instability, such as cracking and collapsing, may not be so obvious today. These slabs were deposited onto a variety of surfaces including weak low density snow and wind scoured areas. Due to the lack of observations from the true alpine country of our area, and the variety of surfaces these slabs were deposited onto, we can not eliminate wind slabs as our #1 avalanche problem for today. It is still possible to trigger a wind slab avalanche today, particularly in the alpine. These areas will be isolated and therefore it will be easy to be lulled into complacency. Evaluate all wind loaded terrain before committing to a slope today.
Recent avalanche activity has been confined to the new snow/old snow interface with the new snow being essentially what has been deposited since last Monday (December 18). This new snow has gained strength but it is still important to assess the upper snowpack for potential weak layers like surface hoar and weak, faceted snow that formed prior to this 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!
Sunday: WMR ski patrol reported wind loading from northerly winds that formed pillows of snow that cracked but did not have the energy to propagate. Skiers in the Skyland area of the Flathead Range reported easterly winds which had redistributed the surface snow. They found a rain crust/surface hoar near the bottom of the snowpack but stability results did not produce any propagation.
Saturday: Skiers in the southern Whitefish Range reported some surface slab formation in open areas but they did not find this slab to be reactive. They did not find evidence of an obvious weak layer or strong slab within the top 2 feet of the snow surface. No other signs of instability were noted.
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.
Christmas Day was cool with mostly dry conditions and 0-4" of new snow over the past 24 hours. Currently, mountain temperatures range from 9-17º F, and winds are out of the southwest at 1-19 mph with gusts from 12-26 mph. Today, temperatures will warm into the mid teens to lower 20's with light southwesterly winds and occasional moderate gusts. Tonight a moist system enters our area bringing snow and windy conditions to all elevtions throughout Tuesday.
| 0600 temperature: | 9-17 deg. F. |
| Max. temperature in the last 24 hours: | 11-17 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 1-19 mph |
| Maximum wind gust in the last 24 hours: | 14-29 mph |
| New snowfall in the last 24 hours: | 0-4 inches |
| Total snow depth: | 50-69 inches |
| Monday | Monday Night | Tuesday | |
|---|---|---|---|
| Cloud Cover: | Dry conditions with seasonal temperatures. | Snow returning to our area with windy conditions. | Moderate to heavy snow with windy conditions. |
| Temperatures: | 17-24 deg. F. | 12-20 deg. F. | 21-30 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 9-12 mph with gusts to 24 | 14-18 mph with gusts to 47. | 17-22 mph with gusts to 40. |
| Snowfall: | 0 in. | 0-2 in. | 5-10 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.
