General Snow and Weather Information

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November 22, 2014 7:30 am by Scott Savage

Bottom Line: Heavy snowfall and strong winds will load a thin snowpack and human triggered avalanches are probable. Where crusts and weak, sugary faceted snow crystals already exist, you could trigger relatively wide, persistent slab avalanches up to 4 feet deep. Be careful this weekend as thin, early season snowpacks are notoriously unpredictable and conditions will vary over short distances.

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

Weather discussion: Heavy snowfall continues through this morning with snowfall diminishing from south to north during the day. By Saturday evening, I expect storm totals of 6-12" in the southern areas and 8-16" in the northern and western portions of the advisory area. Strong S/SW winds shift to the NW and continue into the afternoon. Temperatures cool dramatically from near freezing to the teens F as the snowfall decreases. Sunday, expect mostly cloudy skies with continued snow showers in the north, moderate NW winds, and high temperatures in the teens to 20's F.

Snow and weather history: Small October storms followed by fair weather left "crusty" snow in shady upper elevation areas by Halloween. A Nov 1st storm deposited 3-10" of dense snow at middle and upper elevations throughout the advisory area. A week of generally clear, mild weather followed that storm. Most alpine locations and some shady middle elevation slopes still had significant snow cover following the early November period of fair weather. On Sunday, Nov 9th, a fast-moving storm and associated cold front produced 2-6" of low density snow; in many locations, precipitation appeared to have started as rain before changing to snow. Temperatures cooled dramatically during this small storm and remained unseasonably cold for most of the week. On Nov 13th and 14th, a strong storm dumped 6 inches to 2 feet of new snow in the mountains, favoring the northern and western Smoky's and the Sawtooths. Since then, inversions have kept temperatures warm at upper elevations while the valleys have been cold at night.

Snowpack discussion: The recent fair weather and temperature inversions have likely strengthened the near surface layers above pass level but weakened the snowpack in middle and some lower elevation terrain. On most upper elevation slopes, today's storm and wind-transported snow is being deposited on a relatively thin, early season snowpack containing weak, sugary faceted snow and crusts deep in the snowpack. At middle and lower elevations, I'd expect any pre-existing snow to be weak and faceted as well. Any slab avalanches you trigger have the potential to propagate fairly wide and entrain the entire snowpack to the ground.

What's it mean?: Exercise caution in all steep terrain this weekend and especially on slopes where crusts and/or sugary faceted snow exists. Expect newly formed wind slabs to be sensitive to triggering. Dig quick holes with your hands to see what the snow looks like closer to the ground - if you find sugary, faceted snow crystals or crusts, I'd stick to slopes less than 30 degrees. Natural avalanche activity, snowpack collapses, and shooting cracks are flashing neon signs saying "Danger - unstable snow and avalanches ahead!" The consequences of being caught in even a small avalanche can be especially severe when the snowpack is thin and there are hidden rocks, stumps and trees in the runout.

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General Information

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