Increasing wind speeds yesterday afternoon and overnight have likely drifted snow and formed thin wind slabs on leeward aspects in alpine locations. These slabs will generally be found as isolated pockets in typical favored wind locations. The avalanche danger is MODERATE on upper elevation wind loaded terrain and LOW on all other slopes. Evaluate wind loaded terrain and look for signs of instability like cracking and collapsing.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
After a bout of northeasterly winds, wind direction has returned to a more typical southwesterly flow over the past 36 hours. Wind speeds increased yesterday afternoon and overnight with a maximum wind gust of 42 mph recorded at the Snowslip weather station in John F. Stevens Canyon. Our surface snow is a bit old and worked over but I believe that in favored upper elevation locations, particularly the alpine, this snow is still capable of being transported and forming thin wind slabs. These winds will be with us throughout the day transporting snow onto leeward slopes at upper elevation locations. 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.
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.
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.
Skiers in the Marion Lake area of the Flathead Range Thursday reported up to 3 to 4 inches of new, unconsolidated surface snow on protected aspects, and a layer of faceted snow about 18 inches from the surface that fractured and partially propagated across the column in stability tests at upper elevations. Skiers in the southern Whitefish Range found great skiing, but also layer of small facets about 2.5 feet from the surface that propagated across the column in stability tests.
Fortunately, temperatures have moderated at all elevations compared to Saturday's readings. Over the past 24 hours, only minimal snow has fallen across our advisory area with winds increasing out of the south-southwest. Currently, temperatures above 6000 feet range from -16º to 3º F, and winds are out of the south-southwest at 10-13 mph with gusts from 18-25 mph. Today, temperatures will reach the upper single digits to low teens at upper elevations with light snow and light to moderate winds with occasional strong gusts. A windy period begins tonight and lasts into Tuesday with favored locations receiving sustained moderate winds with strong gusts. Snow will also be on the increase throughout this period.
| 0600 temperature: | -6 to 3 deg. F. |
| Max. temperature in the last 24 hours: | -2 to 3 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 5-17 mph |
| Maximum wind gust in the last 24 hours: | 21-42 mph |
| New snowfall in the last 24 hours: | 0-1 inches |
| Total snow depth: | 10-58 inches |
| Sunday | Sunday Night | Monday | |
|---|---|---|---|
| Cloud Cover: | Light snow with breezy conditions. | Light snow with winds increasing. | Snow with moderate to strong winds. |
| Temperatures: | 8-14 deg. F. | 2-11 deg. F. | 18-24 deg. F. |
| Wind Direction: | West - Southwest | Southwest | West-Southwest |
| Wind Speed: | 10-13 mph with gusts to 25 mph. | 12-16 mph with gusts to 43 mph in the Flathead Range. | 20-28 mph with gusts to 53 mph in the Flathead Range. |
| Snowfall: | 1-3 in. | 1-3 in. | 5-7 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.
