UDOT PLANNED AVALANCHE CLOSURES!!

Forecast for the Salt Lake Area Mountains

Nikki Champion
Issued by Nikki Champion for
Thursday, December 12, 2019
With increased snow and wind the avalanche danger will be on the rise.

Today the avalanche danger is CONSIDERABLE on northerly and east-facing slopes at mid and upper elevations where a persistent weak layer of snow exists 2-4 feet deep. New snow and increased winds will only add stress to this layer making human triggered avalanches likely.

The avalanche danger is MODERATE on southerly-facing and west-facing slopes at mid and upper elevations which don't have the persistent weak layer on the ground. Winds will be increasing throughout the day, on these aspects watch for signs of developing slabs of wind drifted snow, and avoid them.

LOW avalanche danger exists at low elevations which continue to have generally safe avalanche conditions.
Low
Moderate
Considerable
High
Extreme
Learn how to read the forecast here
Special Announcements
Thanks to the generous support of our Utah ski resorts and Ski Utah, we have discount lift tickets available. All proceeds support the UAC. Get your tickets HERE.

Consider taking an avalanche class, there are many different options. Click on the Education menu for a full list of classes from the UAC and other providers. Check out the Know Before You Go eLearning program for free, online, avalanche classes.
Weather and Snow
Snowfall began this morning with a trace to 1.5 inches by 5 a.m. Temperatures this morning are in the upper 20s F at trailhead and low to mid 20s F at ridgetops. Westerly winds at ridgetops are averging 15-20 mph and gusting 25-30 mph.
Snowfall will continue through Saturday with the heaviest snowfall occurring tonight and into tomorrow morning. For today expect 3-5" of snow, temperatures in the mid-teens to upper 20s F, and westerly winds averaging 15-30 mph, and gusting up to 50 mph at ridgelines.
Over the past few days a variety of snow surfaces have been seen, a zipper crust on southerly aspects and surface hoar crystals on almost all aspects. These surface hoar crystals may already be capped an preserved by this morning's snow, and they could develop into a weak layer or poorly bonded interface moving into the weekend. Photo below of surface hoar crystals (M. White).
Total new snow amounts by Sunday could be 1-2 feet. For a complete weather briefing view the video at the bottom of the page under "Additional Info".
Recent Avalanches
Yesterday, one ski area triggered 3 avalanches in the old, weak facets on high elevation, north-facing, steep rocky terrain that had previously not been opened or received any explosive testing. The largest was 150 ft wide and 2 ft deep. These slopes had avalanched naturally during the Thanksgiving storm, and yesterday they produced what we call "repeater" avalanches. These slides are a good warning sign of what will begin happening in the backcountry.
Other avalanches have been occurring sporadically but enough to get our attention. View all of them HERE.
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Avalanche Problem #1
Persistent Weak Layer
Type
Location
Likelihood
Size
Description
As the name suggests, this layer is persistent and needs a lot of time to heal. Any slope facing northerly or east at mid and upper elevations has weak old faceted snow on the ground and a dense 2-4 foot slab on top of it. Moving into another weather system today through the weekend, the additional load and increased stress from new snow and wind could be enough to tip the scales and cause more avalanches on this layer.
Recent avalanches have been clear warning signs. Avoid mid to upper elevation north-facing and east-facing terrain, or stay on slopes below 30 degrees with no slopes above, below or connected that has a slope angle above 30 degrees.
The photo below shows the common snowpack structure, weak, sugary facets with a dense slab on top.
There is good news, with a few inches of refresh southerly facing terrain will continue to have fun riding conditions where this avalanche problem does not exist and possesses a primarily right side up snowpack.
Avalanche Problem #2
Wind Drifted Snow
Type
Location
Likelihood
Size
Description
We have had multiple consecutive days of westerly winds averaging 10-20 mph and gusting above 30 mph at ridgelines. With this storm, the westerly winds will continue and only increase. Expect gusts up to 50 mph at ridgelines today, and up to 60 mph at ridgelines tonight. As the storm continues to develop, the new snow will bond poorly to the old snow surface and we will expect to see wind drifted snow along upper elevation ridgelines and around terrain features such as gullies and chutes, especially into the afternoon.
Look for signs of wind-blown snow which often looks rounded and smooth, and sounds hollow. Other obvious signs include whumpfing, collapsing, and shooting cracks. Also, look for slopes that were scoured or eroded and consider where that snow was transported.
The simple strategy is to look for and avoid these slabs of freshly wind drifted snow on steep mid and upper elevation slopes.
Additional Information
General Announcements
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.