A strong wind event entered our area last night and will last throughout the day. These winds will drift the low density surface snow onto leeward aspects at mid and upper elevations. These winds may deposit this snow at a lower elevation than usual. The avalanche danger is CONSIDERABLE on upper elevation wind loaded terrain and MODERATE on all other slopes. Evaluate wind loaded terrain and look for signs of instability like cracking, collapsing and hollow sounding snow.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Unusual conditions produce unusual avalanches! A strong wind event entered our area last night and will last into tomorrow (Tuesday). Moderate to strong sustained winds with impressive gusts will dominate our weather today. These winds will easily drift the low density surface snow onto leeward aspects. In exposed areas this wind has the potential to deposit snow lower in the starting zone than usual. In extreme cases the snow may end up below the starting zone and deposited in the avalanche path. In some instances this snow will sublimate, or disappear, from our area altogether. Wind slabs formed today are not to be taken lightly. They have the potential to possess hard slab characteristics, meaning instead of breaking beneath your skis or machine they may tend to break well above you on the slope. Hard slabs have the tendency to propagate great distances and encompass low angle terrain. Look for smooth rounded pillows of snow and be cognizant of hollow sounds along with cracking and collapsing in the snowpack. Evaluate all wind loaded terrain before committing to a slope.
Following a somewhat lengty storm free period our area returns to a snowy and windy pattern starting today. Temperatures throughout this storm will rise and deposit progressively denser snow on top of our thick layer of low density surface snow. This is not a good recipe for safe recreating in avalanche terrain. As the new snow accumulates sluffing in this new snow layer will increase. In areas favored by snowfall be alert to the possibility of a storm slab (new denser snow) developing on top of the low density surface snow. This is a surface snow problem and can be identified by cracking and collapsing of the snow under your feet or machine.
In some locations across the advisory area we continue to find buried weak snow/crust combinations. These layers exist 1.5 to 2.5 feet from the snow surface. Recent stability tests illustrate the potential for these deeper weak layers to fracture and propagate across the slope. However, we haven't observed or received reports of avalanche activity on these layers in over 2 weeks. Yesterday, we found depth hoar in a shallow snowpack near the Continental Divide that propagated in our stability test (video). Continue to carefully assess each slope before committing to it. Areas that are particularly notorious for harboring these weak layers are typically steep and rocky with a shallow snowpack.
Sunday, WMR ski patrol observed no propagation in a pit dug within the ski area. They did report several layers that failed within the top 30cm of cohesionless snow and also found buried crusts. Inbounds skiers reported soft slab development in favored windy areas. This slab did not possess the energy needed to propagate. Skiers just east of the ski area observed easy failure in the top 25cm of new snow without propagation. They were able to trigger numerous sluffs during their tour.
Saturday, snowmobilers in the Sixmile area of the Swan Range reported that the snowpack consisted of 2 feet of light surface snow that sat atop a very dense base.
On Friday Guy traveled to the Skyland area in the Flathead Range, just west of Marias Pass. He found a thin snowpack with well developed depth hoar on southerly aspects and in stability tests this layer failed with propagation. On leeward aspects they found a soft surface wind slab that had bonded with the layer below.
Temperatures have moderated at all elevations as a strong southwest flow enters our region. Windy conditions developed overnight and will continue into tomorrow. Over the past 24 hours 1-7" of snow has fallen across our advisory area with winds increasing out of the south-southwest. Currently, temperatures above 6000 feet range from 9º to 16º F, and winds are out of the south-southwest at 13-27 mph with gusts from 25-44 mph. Today, temperatures will reach the upper teens with light to moderate snow and moderate to strong winds. Snow and winds will continue into tomorrow.
| 0600 temperature: | 9-16 deg. F. |
| Max. temperature in the last 24 hours: | 9-16 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 8-30 mph |
| Maximum wind gust in the last 24 hours: | 25-47 mph |
| New snowfall in the last 24 hours: | 1-7 inches |
| Total snow depth: | 39-59 inches |
| Monday | Monday Night | Tuesday | |
|---|---|---|---|
| Cloud Cover: | Snowy and windy. | Light snow with windy conditions. | Continued snow with windy and warmer conditions. |
| Temperatures: | 13-22 deg. F. | 12-20 deg. F. | 28-36 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 20-27 mph with gusts to 48 mph. | 13-18 mph with gusts to 39 mph. | 28-36 mph with gusts to 63 mph. |
| Snowfall: | 5-8 in. | 1-4 in. | 3-7 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.
