General Snow and Weather Information

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November 28, 2014 7:30 am by Scott Savage

Bottom Line: A potent storm will create dangerous avalanche conditions in the Sawtooth and northwestern Smoky Mountains where 15-30" of dense snow and strong W winds are expected through Saturday evening. Natural and human triggered avalanches will become likely by late Friday. The snow will fall on a thin, early season snowpack containing crusts and sugary, faceted layers - larger avalanches that entrain the entire snowpack are possible and both avalanche starting zones and large runout zones should be avoided as the storm develops. In the mountains closer to Ketchum and Fairfield, snowfall amounts will be lighter but the avalanche danger will also increase. We may issue Avalanche Warnings for some areas as the storm develops.

Daily avalanche advisories are tentatively scheduled to begin in early to mid-December (travel conditions dependent).

Weather discussion: An upper level low and strong westerly flow pull abundant moisture into central Idaho today and Saturday, creating heavy snowfall and strong SW to W winds through Saturday afternoon. Snowfall begins Friday afternoon, peaks in intensity overnight, and diminishes Saturday during the day. By Saturday evening, expect 18-30" at upper elevations in the Sawtooths and NW Smoky's, 10-18" near Galena Summit, and 4-12" in the mountains near Ketchum and the Soldier's. Snowfall amounts will be much greater at upper elevations than near the valleys. Strong southwest winds increase and shift westerly today, blowing 30-50 mph on the ridgetops. Mountain temperatures slowly drop from near 30 degrees F during the snowfall event before plummeting to zero F to -20 degrees F Saturday night.

Snow and weather history: Unseasonably warm temperatures over the past few days - and rain to near 8000' in the Sawtooth's - have created widespread crusts at the snow surface. While the warm temperatures have likely strengthened the faceted layers lower in the snowpack, they still exist and remain suspect when they receive a large, rapid load.

What's it mean?: Snowpacks like boring, conservative "lives" - they don't like rapid change. The thought of 20-30" of dense snow in 24 hours makes the hair on the back of my neck stand up…when you add the expected strong winds and surface crusts that formed over the past few days to the equation, ugh. If the snowfall amounts pan out, the avalanche danger will spike dramatically by Saturday morning. Exercise conservative decision making if it's dumping where you're playing today. Reevaluate your terrain choices as the snow piles up - recognize that any upper elevation starting zones above you are likely receiving much more snowfall and wind-transported snow than more sheltered slopes below treeline. Natural avalanche activity, snowpack collapses, and shooting cracks are flashing neon signs saying "Danger - unstable snow and avalanches ahead!"

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General Information

Produced by Sawtooth Avalanche Center.