Wasatch Cache National Forest
In partnership with: Utah Division of State Parks and Recreation, The Friends of the Utah Avalanche Center, Utah Department of Emergency Services and Homeland Security and Salt Lake County.

“keeping you on top”

AVALANCHE ADVISORY

Monday, April 28, 2008
Hello, this is Bruce Tremper with the Forest Service Utah Avalanche Center and this is our end-of-season message.

Our money has run out and we have ended avalanche advisories for the 2007-08 season. This does not mean the end of avalanches. It just means that we have to draw the line somewhere and the end of April is where we usually do it.

Also, spring conditions tend to be much more predictable than winter and our advisories tend to sound like a broken record after awhile. (Does anyone even remember what a broken record used to sound like?) So here are a few boilerplate suggestions for dealing with typical spring conditions:

In spring, we usually have a clockwork-like alternation between snow storms followed by rapid warming and wet sluffs on steep, sun exposed slopes. Thus, your strategy has to rapidly adjust between one of two different avalanche dragons.

Storm Snow:

First, every time we get a fresh snowstorm you will need to deal with all the usual problems of storm snow such as wind slabs and weak layers within the new snow. As always, you should avoid any slope steeper than about 35 degrees with recent deposits of wind drifted snow. They will usually look smooth and rounded and they usually feel “slabby” meaning that harder snow lies on top of softer snow. You will often find them in upper elevation, above-tree-line terrain especially near ridges. In spring, these wind slabs are often short-lived because warm temperatures usually settle them out quickly.

Also, you need to carefully check for weak layers within the new snow even in non-wind loaded snow. Often spring storms will precipitate graupel, that pellet snow that looks like little Styrofoam balls, which behave like little ball bearings. Also, even on non-wind loaded slopes, lighter density snow can also be a weak layer during storms. Again, these instabilities often occur just during or immediately after the storms and settle out quickly in the warm temperatures.

Here’s how you deal with storm snow instabilities: jump on lots of small test slopes to see how well the new snow is bonded, simply dig down with your hand to cut out a little square of snow and pull on it. Finally, never jump into a slope without first putting in a good slope cut. Build up your speed and cut across the slope at about a 45 degree angle aimed at an island of safety so that if the slab does break, in theory, your momentum will take you off the moving slab into safer terrain.

Wet avalanches:

The second avalanche problem will be wet avalanches as the snow gets soggy in the strong spring sun and warmer temperatures. New, dry, cold snow will almost always turn to wet sluffs in a hurry as soon as the sun hits it for the first time. As a precursor, you will usually see roller balls or pinwheels in the new snow as it gets damp, which will later turn into larger, more dangerous, wet sluffs. Normally these sluffs are “manageable” unless one takes you into trees, rocks, over a cliff or into a narrow gully. People usually get into trouble in a couple of ways. First, they start out in dry snow up high and descend into wetter and wetter snow and before you know it, you’ve gotten yourself into a pickle. Second, they simply stay out too late in the day. The name of the game in spring is to start early and head home early.

You can also get into trouble with wet avalanches even in older, “corn” snow—snow that has melted and frozen several times to form larger, grained snow. Many snow connoisseurs live for corn snow, that baby-butt smooth, refrozen surface, which I also call “nature’s groomers.” The trick is to carefully watch the overnight temperatures to make sure the snow surface has refrozen. With cloudy overnight sky, you will need below freezing temperatures, but with a clear sky, combined with dry air, the snow surface can freeze even with overnight lows of around 38 degrees. (See links below for Internet links.) Next, you have to catch it just after the sun has softened up the surface enough so it’s not chattery and icy but before the sun has completely turned it to breakable mush. It’s a fine art, really. You need to start out on east facing slopes in the early morning, switch to south facing at mid morning and west faces by late morning. After noon, you definitely need to be headed home, first, because there is the danger of wet sluffs and second, because your deep tracks in mushy snow will freeze into something resembling concrete traffic barriers and ruin the surface for others the next morning.

Finally, each spring, like clockwork, we get very large, “glide” avalanches on steep rock slabs especially in places like Broads Fork and Stairs gulch in Big Cottonwood Canyon. They occur when meltwater lubricates the interface between the rock slab and the snow and then entire snowpack moves very slowly like a glacier for several days until it releases catastrophically in a huge avalanche. These can occur any time of day or night. So in other words, just avoid the slopes below these big glide cracks in the more radical, steep terrain.

Unfortunately, this spring, we’ve had two major dust storms, which put a thin layer of brown dust on the snow surface, so the snow will probably get much more sun cupped than usual, it will melt faster and it may produce more wet avalanche problems than usual. So be especially careful with the first major, prolonged warm up we have this spring.

Mountain Weather:

We have an embarrassment of riches for mountain weather products on the web. Here is a list of links that I regularly consult for mountain weather information:

Alta Forecast Graph (A wonderful forecast graph from the National Weather Service. This may be the only product you will need.)

48-hour Weather Observations (This is a compilation of the past 48 hour temperature, wind and snow from all the automated weather stations—a php script written by our own Brett Kobernik.)

Penn State Weather (Good weather forecast maps you can loop through.)

University of Utah Weather (The Theta-e time-height is especially powerful if you know how to read it.)
Alta Public Forecast (The good-old, non-technical, forecast for those who want a general summary in plain English and icons.)

Announcements:

We still want to know about any avalanche activity you see, especially if someone is caught, so please leave us a message at (801) 524-5304 or 1-800-662-4140, or email us at uac@avalanche.org. (Fax 801-524-6301)

The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

Thanks for a great season and we will be back around the first of November.