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.

ďkeeping you on topĒ

AVALANCHE ADVISORY

Friday, April 27, 20072:00 pm
Good afternoon, this is Bruce Tremper with the Forest Service Utah Avalanche Center with your backcountry avalanche and mountain weather information.Today is Friday, April 27, 2007 and itís 2:00 in the afternoon.

 

This will likely be the last avalanche advisory for the season.

 

Current Conditions:

Itís been great lately if you like corn snow.We had a good refreeze last night with temperatures just under freezing and the clear skies allow the heat of the snow surface to radiate out into space, making the snow surface colder than the air temperature. But itís all history now because we are having a strong warming for the weekend.

 

Avalanche Discussion:
The warmer temperatures have already started some localized wet sluffs on the high elevation north facing slopes.Wet sluffs were noticed yesterday in upper Little Cottonwood Canyon and Iím expecting much more of them this weekend.

First, I should talk a little about how wet avalanches work.As Iím always saying, snow is just like people, it doesnít like rapid changes.Wet slabs tend to occur the first time that water percolates through a cold, dry snowpack, which is the snowpack equivalent of a person taking a cold, shower.Itís quite a shock at first but after awhile you get used to it.In mid March, we went through a big wet slab avalanche cycle when the cold, dry snowpack warmed up for the first time.But the temperatures were not warm enough to make the upper elevation north facing slopes get soggy.When Craig Gordon and I checked the snowpack this morning, we found lots of cold, dry snow above 9,500í on northwest through northeast facing slopes.In fact, we also found some of our old enemy, the cold, dry, faceted snow on slopes where the snowpack is less than two feet deep.In other words, most other slopes have already gone through their wet avalanche cycle, but the last to go are always the upper elevation north facing slopes, and it looks like it will get warm enough this weekend to make them active.

Weíre expecting temperatures in the mid 80ís in Salt Lake this weekend and in the mid 60ís at 8,000í, and the mid to upper 40ís on the ridge tops.In addition, the overnight lows will not drop below freezing for several nights, starting tonight.Combined with a clear sky, the snow surface radiates its heat into empty space, which allows it to cool down below the air temperature.Thus, we may get a superficial refreeze tonight and through the weekend especially in the mountain basin bottoms where the cool air pools, but once you get up on the slopes it will likely be less supportable.

The bottom line is that you should watch out for northwest through northeast facing slopes above 9,500í for the next several days.If you must go onto them, do it in the morning before they get wet and definitely get off of them after noon.Itís counterintuitive, but the south facing slopes (which face directly into the sun) may actually be safer because they have already gone through their wet avalanche cycle and they have well established drainage systems, similar to a summertime snowpack.Remember that most of the ski areas are closed for the season and no one is doing any avalanche control or rescue.

Mountain Weather:

Itís going to be a real cooker for the next several days with sunny skies, light winds and 8,000í temperatures in the mid 60ís.Ridge top temperatures will be around 50 degrees and it will be 40-45 degrees on the highest peaks.The peak of the warming should be Saturday and Sunday and it will cool down slightly for a couple more days with a strong cooling on Thursday.

Announcements:
UDOT highway avalanche control work info can be found HERE or by calling (801) 975-4838.

Our statewide tollfree line is 1-888-999-4019 (early morning, option 8).

For our classic text advisory click HERE.

We appreciate all the great snowpack and avalanche observations weíve been getting, so keep leaving us messages at (801) 524-5304 or 1-800-662-4140, or email us at [email protected]. (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.

This will likely be the last avalanche advisory for the season and we will issue an end-of-season message on Monday
.