Wasatch Cache National Forest

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Avalanche advisory

THURSday,  FEBRUARY 21, 2002  3:30 pM

 

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Good afternoon, this is Evelyn Lees with the Forest Service Utah Avalanche Center with your backcountry avalanche and mountain weather advisory.  Today is Thursday, February 21, 2002, and it’s 3:30 p.m.

 

Current Conditions:

Under mostly clear skies, mountain temperatures have climbed to near 30 at 10,000’, and winds are light out of the west.  Yesterday’s storm rather evenly distributed the snow, with about 10 inches in Big Cottonwood and the Ogden, Park City and Provo mountains, and up to 16 inches in Little Cottonwood.  The new snow was denser than our usual Wasatch powder, ranging from 10 to 15 percent water content.  During the storm, the west and northwest winds were very strong along ridges and in open bowls. 

 

Avalanche Conditions:

There have been three distinct patterns of avalanche activity today – avalanches breaking within the new snow from yesterday or Monday, slides breaking into the more deeply buried faceted weak layers, and wet snow activity from heating.

 

New snow instabilities settle out rapidly and today’s observers are reporting mostly stubborn, pockety activity within the new snow, breaking on the density inversion in Monday’s few inches of light snow.  So while much of the new snow has stabilized, there are certainly a few drifts that will still be sensitive on steep slopes, especially at wind exposed upper elevations where the most drifting was occurring yesterday. 

 

Many slopes in our forecast areas have layers of more deeply buried weak faceted snow.  Although there was not enough weight added by this storm to start a major avalanche cycle, there are areas where slopes are right on the edge.  There were reports of 2 remotely triggered slides from the Provo mountains today that broke on these weak faceted layers.  They were on steep, northeasterly facing slopes at about 9,000’, broke out 1 ½ to 3’ deep, about 100’ wide and piled up debris 4 to 5’ deep.  Some of these slopes with weak underlying snow exist at all elevations and in most areas, but the weaknesses are especially prevalent on mid and lower elevation shady slopes.  Weak underlying snow is particularly widespread in the Provo and Park City mountains, in the Mill Creek drainage and in the Uinta Mountains.   A slide triggered with in the new snow may be able to step down into one of these deeper weak layers.

 

And finally, heating and direct sun caused some wet loose snow sluffs today, and I expect this problem to be more widespread tomorrow.  Thin clouds tomorrow could also help warm even the shady slopes.  So if you find the snow getting wet and mushy, get off of and out from under steep slopes.

 

Bottom Line: 

The danger of human triggered avalanches is MODERATE on slopes of about 35 degrees and steeper, especially with recent deposits of wind drifted snow.  With day time heating on Friday, the danger may rise to CONSIDERABLE on and below steep slopes. The danger is lower in areas that received less than about 6 inches of new snow.

                                                                                                                      

(Provo Area Mountains)

The danger of human triggered avalanches is CONSIDERABLE on and below steep slopes in the Provo Mountains, especially where wind loaded. 

 

(Ogden Area Mountains)

The danger of human triggered avalanches is MODERATE on steep slopes in the Ogden Mountains, especially on wind loaded, upper elevation slopes and on shady low and mid elevation slopes.

 

(Western Uinta Mountains)

The danger of human triggered avalanches is CONSIDERABLE on steep slopes, especially with recent deposits of wind drifted snow.  Human triggered avalanche are likely and natural avalanches possible.

 

Mountain Weather:

High pressure will remain over Utah for tonight and Friday.  Tonight, there will be mostly clear skies light with winds from the northwest.  10,000’ temperatures will continue to warm, reaching near freezing by dawn.  8,000’ lows will be in the mid 20’s.  Friday will be much warmer, with highs in the upper forties at 8,000’ and mid 30’s at 10,000’, and a few high thin clouds moving past.  Then there will be strong winds Friday night ahead of Saturday morning’s fast moving cold front.

 

General Information:

To report backcountry snow and avalanche conditions, especially if you observe or trigger an avalanche, you can leave a message at (801) 524-5304 or 1-800-662-4140.  Or you can e-mail an observation to [email protected] .org, or you can fax an observation to 801-524-6301.

 

During the Olympics, we will issue both morning and afternoon advisories.  We’ll use the 364 -1591 line for more detailed or additional avalanche information.  Wasatch Powderbird Guides will not be flying during the Olympics. 

 

We have a new icon-based, short advisory posted each day at www.avalanche.org.  We would appreciate any feedback on this new product.

 

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. 

 

Bruce Tremper will update this advisory by 7:30 Friday morning.

Thanks for calling!

_____________________________________________________________________________

For more detailed weather information go to our Mountain Weather Advisory

National Weather Service - Salt Lake City - Snow.

For an explanation of avalanche danger ratings:

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