Avalanche Advisory
Advisory: Salt Lake Area Mountains Issued by Trent Meisenheimer for Monday - March 12, 2018 - 4:11am
bottom line

The avalanche danger is MODERATE - large avalanches 2 to 5 feet deep can be triggered in isolated areas - avoid steep slopes facing northwest through southeasterly at the mid and upper elevations.

Warm temperatures and periods of sun will heat the snow, and wet loose avalanches can be triggered on all aspects on mid and low elevation slopes and on steep, sunny slopes later today.

Roof-avalanches are occurring as snow slides off building roofs, with debris piles deep enough to bury and kill a person.




special announcement

Alta Ski Area will close Grizzly Gulch on Today March 12th for helicopter rescue training. Grizzly Gulch is private property. Please respect this closure.

Alta may close access to Grizzly Gulch during upcoming storm events until avalanche mitigation on Patsey Marley is complete.

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current conditions

Under partly cloudy skies it should be a beautiful sunrise - Above 9,000' overnight temperatures hovered around freezing 32°F. Below 9,000' temperatures are above 32°F. Winds are calm, generally from the south and west, with even the highest elevation anemometers hardly spinning. Overnight temperatures just barely dropped below freezing so you can expect a shallow re-freeze of the snowpack surface and many of the crusted aspects will warm and soften quickly today. Upper elevation northerly facing slopes still hold dry soft snow.

recent activity

Another slab avalanche was triggered yesterday by a snowmobiler in the Guardsman's Pass area. It was on a SE facing slope at 9500' in elevation. This avalanche failed initially as a wind slab and quickly stepped down to the ground. It was 150' wide, and up to 6' deep, running 500' downslope. Nobody caught. (see pic below).

A long running wet avalanche was also observed in the south facing White Pine Chute by UDOT at 3:00 pm yesterday. They noted it was the largest wet slide of the season. It's been a wild week - HERE is a list of all the recent avalanche activity, it's worth clicking around and seeing the carnage from the past week.

Photo: Andrew Nassetta - Yesterday's sled triggered slab avalanche from Guardsman area.

Avalanche Problem 1
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Over the past seven days we have seen a number of close calls and large avalanches being triggered by people. These avalanches have been 2' to 5' deep and up to 800' wide. There are two weak layers responsible and both have been avalanching consistently over the past week. One of the weak layers can be easily found just below the February 18th dust layer (dig down 3' feet) to find a thin strip of weak faceted snow roughly 2-6" below the dust layer. The other layer of concern is the faceted snow from early November at the ground or just above the ground.

This activity has led us to change from a persistent slab problem to a deep slab problem. Both persistent slab and deep slab avalanches are caused from weak faceted snow buried in the snowpack. The main difference - the slides are larger, deeper, and typically involve the release of seasons snowpack, or a layer that is buried more than 3' feet deep.

Deep slab avalanches are hard slabs, typically difficult to trigger and very destructive. "Most people that get caught in one get killed. This makes it very difficult to learn from a close call. Your first encounter with a Deep Slab avalanche could very well be your last." The most suspect slopes are steep mid to upper elevation north-west through south-east facing slopes, especially those that have been loaded by the wind.

CONFUSED? Below are two links to help us understand this transition.

  • Read this write up by the Colorado Avalanche Center on Deep Slab Avalanches. HERE
  • Read this blog post by Brian Lazar on transitioning from Persistent Slab to Deep Slab. HERE​

Photo: (Meisenheimer) - Saturday's deep slab avalanche in Guardsman's Pass area.

Avalanche Problem 2
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 12 hours
description

Wet Loose: As the temperatures warm into the 30s and 40s today, the snow will once again become wet and sloppy. Rider triggered or natural wet loose avalanches will be possible on all aspects and elevations except the mid and upper northerly facing slopes. This is an easy problem to avoid. When the snow surface becomes damp or you start seeing roller balls cascading down from above - it's time to change to a cooler, more shady aspect, or go home.

Cornices have softened and are sensitive, often breaking back further than expected, on what looks like flat terrain. So give them a wide berth and avoid travel below them.

Roof-avalanches: Buildings are starting to shed their winter snow, so look up and avoid travel below steep roofs.
weather

Partly to mostly cloudy skies and warming temperatures are on tap for today. Mountain temperatures will climb into the 30's and 40's. Winds will remain from the south and west blowing 5-15 mph at the upper elevations. The warming trend will continue into Wednesday, with a chance for mountain snow and cooler temperatures late in the week.

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.