Advisory: Salt Lake Area Mountains | utahavalanchecenter.org

Avalanche Advisory

Advisory: Salt Lake Area Mountains	Issued by Drew Hardesty for Wednesday - February 21, 2018 - 5:24am

bottom line

Areas of CONSIDERABLE danger exist in localized terrain on steep northwest to north to northeasterly facing slopes at the mid and upper elevations. Human triggered avalanches 1-3' deep are possible and may be triggered from below. Lingering wind slabs may still be triggered in steep wind drifted terrain and more commonplace in areas with an easterly component. Careful snowpack evaluation, cautious route-finding and conservative decision making remains essential today.

The Good News: excellent and safer skiing and riding conditions can be found on non-wind loaded southerly aspects. If headed to northerly terrain, the smart money stays on low angle slopes with no overhead hazard (ie-connected to steeper slopes above or adjacent to you).

special announcement

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current conditions

Skies are partly cloudy with winds out of the west-southwest blowing 10mph, gusting to 15. Mountain temperatures are the coldest of the season. It's Ice Station Zebra with temps down to -5°F along the ridgelines and as low as -10°F at the Spruces trailhead in mid-BCC. The wind chill registers as -24°F along the exposed ridgelines. Skiing and riding conditions are much improved and coverage now sits at 65-80" in the higher elevations of the Cottonwoods and the PC ridgeline.

recent activity

Avalanche activity reported from yesterday:

Clayton Peak - skier triggered wind slab 1' deep and 30' wide NE at 10,600'
Brighton periphery - skier triggered soft slab 8-12" deep and 70' wide NE aspect at 10,000'
Red Rocks area of PC ridge - skier triggered wind slab 1' deep East facing at 9500'
Cinder Chutes area of PC ridge - skier triggered wind slab 1' deep East facing at 9500'
Ski area control work produced some wind and storm slabs with ski cuts and explosives. An outlier - a ski cut that pulled out a 3' deep but only 15' wide pocket into old weak faceted snow at 8800' on a north facing slope in mid-LCC.

My own party experienced two very large, loud, resounding collapses and triggered a part of the hangfire while investigating Monday's close call in Toots-To-Boot in Alexander Basin of Mill Creek. Below ski guide and avalanche educator Allison Conover explains what we found at the slide. (YouTube link)

Avalanche Problem 2

type	aspect/elevation	characteristics
		LIKELIHOOD LIKELY UNLIKELY SIZE LARGE SMALL TREND INCREASING DANGER SAME DECREASING DANGER over the next 24 hours
description There's too much uncertainty. Two to three inches of snow-water-equivalent over the past week and strong southerly pre-frontal winds Saturday night into Sunday have clearly stressed - at the very least - thinner snowpack areas or areas that have avalanched previously this winter. At least five avalanches - some natural, some human triggered - have stepped into older faceted snow the last two days (Toots, Davis Gulch, West Monitor, mid-LCC control work, skier remote in the Provo mountains - all northwest through east). Loud, deep, guttural collapsing of these layers continued into yesterday, offering little reassurance of, well, much. Monday's Toots-To-Boot avalanche very well demonstrates the mercurial character of a persistent slab avalanche. The very experienced party skied on low thirty-degree terrain and it wasn't until the second person on the slope skied that it propagated back up and across the landscape to where the terrain reached the 44° steep headwall, pulling the whole thing down 300' wide. Standing just off to the side, the first skier watched the slide roar down, coming within 10' feet from where he was standing. Spatial variability exists across the range and across the slope. Areas most suspect are drainages of Mill Creek canyon, the Park City ridgeline, Summit Park, Mt Aire, Snake Creek - all areas along the periphery of the Cottonwoods. This is not to say the Cottonwood get the hall-pass; it's just that many riders may be able to get away with more...until they can't anymore. This structure showed its cards with noticeable stress cracks as low in 8500' . Slope-scale, the strength and structure can vary widely and wildly across the slope - many areas we dug near the Toots avalanche were not that alarming.

type

aspect/elevation

characteristics

LIKELIHOOD

LIKELY

UNLIKELY

SIZE

LARGE

SMALL

TREND

INCREASING DANGER

SAME

DECREASING DANGER

over the next 24 hours

description

There's too much uncertainty. Two to three inches of snow-water-equivalent over the past week and strong southerly pre-frontal winds Saturday night into Sunday have clearly stressed - at the very least - thinner snowpack areas or areas that have avalanched previously this winter. At least five avalanches - some natural, some human triggered - have stepped into older faceted snow the last two days (Toots, Davis Gulch, West Monitor, mid-LCC control work, skier remote in the Provo mountains - all northwest through east). Loud, deep, guttural collapsing of these layers continued into yesterday, offering little reassurance of, well, much.

Monday's Toots-To-Boot avalanche very well demonstrates the mercurial character of a persistent slab avalanche. The very experienced party skied on low thirty-degree terrain and it wasn't until the second person on the slope skied that it propagated back up and across the landscape to where the terrain reached the 44° steep headwall, pulling the whole thing down 300' wide. Standing just off to the side, the first skier watched the slide roar down, coming within 10' feet from where he was standing.

Spatial variability exists across the range and across the slope. Areas most suspect are drainages of Mill Creek canyon, the Park City ridgeline, Summit Park, Mt Aire, Snake Creek - all areas along the periphery of the Cottonwoods. This is not to say the Cottonwood get the hall-pass; it's just that many riders may be able to get away with more...until they can't anymore. This structure showed its cards with noticeable stress cracks as low in 8500' . Slope-scale, the strength and structure can vary widely and wildly across the slope - many areas we dug near the Toots avalanche were not that alarming.

Avalanche Problem 3

type	aspect/elevation	characteristics
		LIKELIHOOD LIKELY UNLIKELY SIZE LARGE SMALL TREND INCREASING DANGER SAME DECREASING DANGER over the next 10 hours
description Lingering wind drifts may stll be sensitive to human weight in steep wind loaded terrain and most pronounced on north to east to south facing slopes that may have been loaded or cross-loaded beyond ridgelines and other terrain features.

weather

We'll see increasing clouds with the first of many generally weak weather systems on tap for northern Utah. For today, winds will be from the south and southwest at 10-15mph. Temps will generally remain in the freezer for awhile...today they'll be in the single digits up high and the low teens at the mid-elevations. Saturday night into Sunday holds the best promise for additional snowfall.

general announcements

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This information does not apply to developed ski areas or highways where avalanche control is normally done. 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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