Wasatch Cache National Forest

In partnership with: The Friends of the Utah Avalanche Forecast Center, Utah Department of Public Safety Division of Comprehensive Emergency Management, Salt Lake County, and Utah State Parks

The Utah Avalanche Center Home page is: http://www.avalanche.org/~uac/

Avalanche advisory

Thursday, March 20, 2003

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Good Morning. This is Ethan Greene with the Forest Service Utah Avalanche Center with your backcountry avalanche and mountain weather advisory. Today is Thursday, March 20, 2003, and it’s 7:30 in the morning.

Current Conditions:

Last night under clearing skies temperatures dipped into the mid to upper 20’s at 8,000’ and low 20’s at 10,000’. The winds have been from the south and southwest in the 5 to 10 mph range, and there is a trace of new snow this morning.

Yesterday there were both low and high level clouds over the mountains. The high clouds were quite thin by mid day, but the low clouds lingered all day in some areas. As a result the snow surface conditions will be a bit variable today. In general there are firm crusts below 8,000’ on all aspects and thin crusts on all but the northerly aspects below about 9,000’. If you’re searching for soft snow your best bet will be a mid or upper elevation slope that is sheltered from the sun.

Avalanche Conditions:

There was a variety of avalanche activity in the Wasatch Range yesterday. Avalanche control work produced 9 significant slides in Little Cottonwood Canyon. Most of these slides took out the new snow from last week and ran on density changes within the new snow layering or firm crusts that formed prior our last stormy period. At least two of these slides broke into deeper weak layers buried in the old snow. The new snow slides were generally a foot deep and 200 feet wide, but a couple were 4 feet deep and 400 feet wide. The deep slab avalanches were over 4 feet deep and about 200 feet wide with one running 2000’ vertically. These avalanches released from steep slopes that face northwest, northeast, and southwest and were all above 10,000’. Although they were triggered with explosives, the snow seemed fairly sensitive probably could have been triggered by a backcountry traveler.

Other avalanche activity from yesterday included natural wet sluffs off steep sun exposed slopes, a natural avalanche off rock slabs in Broads Fork, and human triggered wet sluffs on steep slopes below 8,500’. The human triggered avalanches were only 6 inches deep, but with aggressive ski cutting folks were able to get slides over 50’ wide to run several hundred feet vertically and they entrained a fair amount of snow on the way down.

Over the last few days were there has been a lot of avalanche activity in the new snow layers. These slides have generally been less than a foot deep and 100 feet wide. Time and warm temperatures have helped to stabilize the new snow, but we are not out of the woods yet. Although the areas where you can trigger a slab avalanche have decreased, if you trigger an avalanche today is will likely be several feet deep and over a hundred feet wide. The danger from these avalanches is greatest on steep upper elevation slopes that were wind loaded in the last storm. We had both north and south winds during the last week so look for loading in unusual places.

Today will also be the first day since the storm with extended periods of direct sun. The surface snow has been zapped by the heat, but natural point release avalanches are possible on steep sun exposed slopes today.

Finally, there remains an isolated chance of triggering an avalanche breaking into deeply buried faceted snow on a steep slope with a shallow snowpack above 9,500’.

Bottom Line (SLC, Park City, Ogden, and Provo Area Mountains)

Today there is a MODERATE danger of human triggered avalanches on slopes steeper than 35 degrees with recent wind drifts. These avalanches will be larger and more dangerous than they have been during the last week, and the danger is greatest on upper elevation slopes. Daytime heating will cause the danger of wet slides to increase during the day. The danger from wet slides could rise to CONSIDERABLE today. There is also a MODERATE danger of triggering deeper avalanches on slopes above 9,500 feet.

Western Uintas – call 1-800-648-7433 or click here for weekend and holiday forecasts.

Mountain Weather:

A short wave will move into northern Utah today. The ridge will cause the cloud cover to decrease through mid day, but high clouds ahead of the trough should move over the Wasatch this afternoon. Temperatures will rise into the mid 30’s at 8,000’ and low 20’s at 10,000’. The winds will gradually shift from the southwest this morning to the northwest this afternoon. Wind speeds will be in the 5 to 15 mph range most of the day. Snow flurries are possible this afternoon. Expect partly cloudy skies and mild temperatures on Friday and Saturday with a stronger system forecast for Sunday.

General Information:

Wasatch Powderbird Guides will be flying today in the Days, Cardiff, Silver and White Pine drainages with a home run in Grizzly Gulch. For more information call 801-742-2800.

To report backcountry snow and avalanche conditions, especially if you observe or trigger an avalanche, please leave a message on our answer machine at (801) 524-5304 or 1-800-662-4140, or email to uac@avalanche.org or fax to 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.

Tom Kimbrough will update this advisory by 7:30 on Friday morning.

Thanks for calling!

________________________________________________________________________

National Weather Service - Salt Lake City - Snow.

For an explanation of avalanche danger ratings:

http://www.avalanche.org/usdanger.htm