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Forecast for the Logan Area Mountains

Toby Weed
Issued by Toby Weed for
Monday, December 24, 2018
MODERATE: The snow in most areas is stable and the avalanche danger is generally LOW, but heightened avalanche conditions exist on some drifted upper elevation slopes. You could trigger avalanches involving fresh wind-drifted snow. Dangerous hard slab avalanches failing on a sugary buried persistent weak layer are unlikely yet remain possible on isolated very steep upper elevation slopes with poor snow structure. Evaluate snow and terrain carefully.
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Weather and Snow
A little bit of light snow fell in the Logan Zone overnight, and you'll find nice shallow powder, stable snow, and Low avalanche danger in most areas. Exceptions will be on drifted upper elevation slopes where human triggered avalanches involving fresh or older wind drifted snow are possible. Looks like a dusting to an angry inch of new snow in the mountains this morning, but the remote sensors aren't updating.
It's 17º F at the 9700' CSI Logan Peak weather station, with 15 to 20 mph westerly winds.
A series of weather disturbances will bring periodic precipitation to much of the area through the upcoming week. We'll see snow in the mountains today, with 1 to 3 inches of accumulation possible. Expect a high temperature at 8500' near 26º F and 9 to 13 mph west-southwest wind. Snow is likely tonight, with 1 to 3 inches possible, low temperatures around 15º F, and 8 to 11 mph southwest wind, veering from the southeast in the evening. Snow is likely in the mountains on Christmas Day. High temperatures around 29º F and 10 to 15 mph east winds are expected.
Recent Avalanches
No avalanches were reported over the weekend, but yesterday I found evidence of a small natural involving freshly wind drifted snow in the Peterson Hollow fire scar.
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Avalanche Problem #1
Wind Drifted Snow
Type
Location
Likelihood
Size
Description
Heightened avalanche conditions exist on upper elevation slopes, and you could trigger avalanches consisting of wind drifted snow. Drifting occurred in exposed terrain much of last week, and there are some deeper hard wind slabs lurking under the fresh snow in places. Moderate east and southeast winds are expected on Christmas Day, which could create sensitive drifts at upper elevations in unexpected or unusual places.
  • Watch for and avoid fresh or older drifts on the lee sides of major ridges and in and around terrain features like cliff bands, scoops, gullies, stringers, and sub-ridges.
  • Avoid steep slopes that have a smooth, rounded appearance, or that sound hollow like a drum.
  • Hard wind slabs have a nasty tendency to let you get well out on them before releasing.
  • Cracking in the snow is a red flag indicating potential instability.
Avalanche Problem #2
Persistent Weak Layer
Type
Location
Likelihood
Size
Description
Although quite unlikely, dangerous human triggered hard slab avalanches failing on a persistent weak layer near the ground called depth hoar remain possible on upper elevation slopes. Avoid very steep previously drifted slopes with poor snow structure, including shady or rocky terrain at upper elevations.
The shallow snow on the ground in many areas has become loose, sugary, and faceted in the past couple weeks. I found particularly weak snow in the backcountry near Beaver Mountain, where the total snow is only about 2-feet-deep or less. In these areas the snow is currently stable despite it's weakness, but it'll get interesting when we get significant accumulation in the future.
Sugary, faceted snow from the Thanksgiving storm creates a persistent weak layer near the ground on slopes with shallow snow cover. This from 12/20/18, on a west facing slope at 8500' on Beaver Mountain's backside.
Additional Information
Have a safe and happy Christmas. I will update this advisory Wednesday morning.
General Announcements
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This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.
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