Heightened avalanche conditions exist due to reactive persistent slab instabilities and fresh wind loading following last weekend's storm. Recent reports of collapses in the Flathead Range highlight the potential for triggering a large and dangerous avalanche. Carefully assess the snowpack before committing to steeper terrain.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
Monday's avalanche burial in the Northern Whitefish Range exemplifies our persistent slab avalanche problem. In the Flathead Range, persistent slabs 3 to 5 feet thick over weak facets or faceted crusts lurk on slopes that didn't shed during our recent avalanche cycles. These slabs have been reactive to human triggers following our most recent storm, especially in the eastern portion of the forecast area, evidenced by several reports of a collapsing snowpack. Use cautious terrain selection, and avoid traveling on or directly below slopes harboring poor snowpack structure (as demonstrated in this video). This type of avalanche can be triggered remotely from below or adjacent to a connected slope. Shooting cracks or collapses are clear indicators of unstable conditions.
Slabs of recently drifted snow can be triggered in steep, leeward terrain at higher elevations. Observers on Monday and Tuesday reported fresh drifts and wind slab formation. These slabs could drag you into a terrain trap or be large enough to bury you on heavily wind loaded features. Look for evidence of recent wind drifting such as blowing snow or smoooth, lens shaped pillows, and avoid wind loaded or crossloaded terrain features.
Our last storm and avalanche cycle ended on December 30th. Storm instabilities are gradually mending, and we removed storm slabs from the problem list today. Keep an eye for isolated exceptions, evidenced by cracking snow. Look for and avoid recent wind drifting at higher elevations, especially in the Flathead Range which has seen gustier winds.
The main avalanche problem concern today stems from the facets or faceted crusts that were buried in mid December following our prolonged drought. Skiers in the John F Stevens Canyon reported several collapses yesterday and snowmobilers in the Northern Whitefish Range triggered a number of persistent slab avalanches on Monday, one of which resulted in a partial burial. Our weak layers were widespread, especially at mid and upper elevations, prior to our December storm cycles (Remember this video?) Subtleties in storm totals, previous avalanche activity, wind loading, temperatures, and a freezing rain event have now created a complicated pattern of which slopes remain problematic. Noisy Basin in the Swan Range has the deepest, warmest, and strongest snowpack. In general, the further you migrate north or east of this bullseye, the shallower and more reactive the persistent slab problems are, but there is a lot of uncertainty and slope to slope variability to this general pattern. When the snowpack is the question, terrain is the answer. You can always default to simpler terrain to manage uncertainty regarding this potentially destructive avalanche concern. Simpler terrain means lower slope angles, shorter vertical relief, more slope support or anchors, and/or fewer terrain traps.
The tree well fatality over the weekend is a tragic reminder to maintain visual or voice contact with your partners while riding in the deep, unconsolidated powder conditions this week.
The Flathead Avalanche Center presents two engaging and free one-hour Avalanche Awareness talks this week. Join us at at Stumptown Snowboards in Whitefish on Wednesday, January 3, from 7 PM - 8 PM ro Stonefly Lounge in Coram on Thursday, January 4, from 7 PM - 8 PM. The class includes general information about avalanche hazard, how to avoid it, and proper equipment for traveling in avalanche terrain. . Contact [email protected] with any questions.
A weak shortwave embedded in a high pressure ridge will bring a few snow flurries today. A warming trend continues with temperatures rising from the teens into the upper 20s today under light winds. The ridge continues its eastward migration on Thursday, bringing our final day of mild, sunny weather before a Pacific storm makes landfall on Friday.
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Cloud Cover: | Snow flurries | Decreasing clouds, inversion developing. | Mild and sunny |
| Temperatures: | 23 to 28 deg. F. | 1 to 6 deg. F. | 25 to 30 deg. F. |
| Wind Direction: | West | Southwest | Southwest |
| Wind Speed: | 0 to 10 | 0 to 10 | 0 to 10 |
| Snowfall: | 0 to 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.
