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Forecast for the Salt Lake Area Mountains

Mark Staples
Issued by Mark Staples on
Sunday morning, December 23, 2018
It remains possible to trigger a slab of wind drifted snow today. Look for signs of wind loading which are areas with smooth rounded or pillowly looking snow. These are typically found downwind of slopes where the wind has scoured or removed snow. An isolated chance exist of triggering a larger slab avalanche breaking near the ground mainly in areas with thinner snow on N and NE aspects.
For today the avalanche danger is MODERATE at upper elevations and MODERATE at mid elevations facing NW->N->E. The danger is LOW elsewhere.
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Weather and Snow
The storm that ended yesterday generally delivered 4-6 inches of snow with a few places in the upper Cottonwoods receiving 8-10 inches. The bigger issue was strong W and NW winds with this storm that were gusting yesterday morning 30-45 mph.
This morning mountain temperatures are mostly in the upper teens F under mostly cloudy skies. Winds shifted slightly and are blowing from the WSW at 10-15 mph gusting to 20 mph.
Today temperatures should rise into the 20's F and winds will remain about the same as they are this morning. This afternoon a few snowflakes may fall but not accumulate. Tonight about 2-4 inches of snow should fall with maybe another inch or so falling tomorrow morning. The storm that was supposed to bring snow over Christmas should drop further south and only bring clouds to northern Utah followed by very cold temperatures.
Recent Avalanches
Yesterday at ski areas and in the backcountry, most avalanches were slabs of wind drifted snow and sluffs of new snow. Go HERE for the full list. See the bottom of this page for photos. There were two notable slides.
  1. A skier unintentionally triggered a slide in Days Draw in Days Fork that was reported 175 feet wide and breaking 2 feet deep near the ground. They were not carried by this avalanche. See discussion below under Avalanche Problem #2.
  2. A person triggered a wind slab when ski cutting the east face of Reynolds Peak. The slab was harder and deeper than he expected and carried him a short distance before he was able to escape to the side. This avalanche broke 80 feet wide and 2 feet deep on a layer of graupel that fell last Wednesday.
Photo below of the slide on Reynolds Peak (Coyne).
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Avalanche Problem #1
Wind Drifted Snow
Type
Location
Likelihood
Size
Description
Yesterday's W and NW winds formed fresh slabs of wind drifted snow that were easily triggered. More are possible today but they should be less sensitive and a little harder to trigger. Hard slabs of wind drifted snow like the one on Reynolds peak (photo above) will be the toughest to deal with. Being so stiff, they can let you ride further onto them before they release.
Today's winds are not too strong, but they are blowing a little more southerly and may have formed a few more wind slabs in new places compared to yesterday. Look for these mainly above 9500 feet, but watch for them at any ridge or sub-ridge where you see evidence of wind.
The photo (M. DiBiaso) below of Toledo Chute is a good example of cross loading in which winds blew across the rideline formed a slab in the gully. There does not appear to be a slab of wind drifted snow further right in the photo were there are ski tracks and no avalanches.
Avalanche Problem #2
Persistent Weak Layer
Type
Location
Likelihood
Size
Description
Remember this problem? Old snow that on the ground prior to Thanksgiving formed a persistent weak layer of sugary, faceted snow crystals. Many slab avalanches slid on this layer in late November and early December. This layer has been dormant since then; however, yesterday's avalanche in Days Draw is a good heads up that this problem still exists. What stands out to me is that this slide broke at the ground but was only 2 feet deep.
On many slopes where the snowpack is 3-4 feet deep, this layer has adjusted to the load on top of it and appears to have gained some strength. On many other slopes with thinner snow (2-3 feet deep), this layer remains weak. There are two reasons some slopes have a thinner snowpack: they avalanched previously OR they are in areas that have received less snow this month. The slope in Days Draw likely avalanched in late November.
What to do? As shown in the aspect/elevation diagram, this layer exists on many slopes. However, it is weakest on slopes with a snowpack less than 3 feet deep on N and NE aspects above 9000 feet. Go to other slopes.
Additional Information
Photo below of a slab of wind drifted snow in Snake Creek (A. McLean)
Photo below of a slide on Mt. Tuscarora in upper Big Cottonwood Canyon (C. Gordon).
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This information does not apply to developed ski areas or highways where avalanche control is normally done. This forecast is from the U.S.D.A. Forest Service, which is solely responsible for its content. This forecast describes general avalanche conditions and local variations always occur.
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