Manti-La Sal Avalanche Center

US Forest Service Manti-La Sal National Forest               

Introduction:  Good morning!  This is Evan Stevens with the USFS Manti-La Sal Avalanche Center.  This is your avalanche and mountain weather advisory.  Today is Monday, February 21st, 2005 at 7:30 am.  This bulletin is sponsored in part by Western Spirit, offering cycling adventures in Moab and beyond, proud sponsors of the Friends of the Manti-La Sal Avalanche Center.  This advisory will expire in 24 hours.

 

To see past advisories check out the ARCHIVE.  To see current conditions go to our WEATHER PAGE.  To see photos go to the AVIPHOTOS page.

 

General Conditions:

We got another 4” of snow at the Geyser Pass Trailhead yesterday.  That means we got almost a foot of snow out of this storm at the trailhead.  The wind has been moving snow throughout the storm and will continue to do so today.  The snow is wind affected well into the trees, and slopes are wind loaded far below the ridgelines.  The more open North through East aspects have sizeable wind slabs sitting on them.  The wind has also done a great job of cross loading some unexpected slopes.  Again the sheltered treed runs are holding the best powder right now.

The road to the Geyser Pass Trailhead was plowed yesterday; a big thanks to the Grand County Road Crew.  4WD or chains (or both) will be useful for driving up there. 

 

Current Conditions: (click location for latest data)

Geyser Pass Trailhead (9,600’):  58” at the stake, it is 18 degrees at the TH at 6:00 am. 

Pre-Laurel Peak (11,700’): AARRGGHH!  Back to the drawing board on this one, hopefully by Monday evening we’ll have read-outs.   

Gold Basin and South Mountain:  82” of settled snow on the ground. 

 

Mountain Weather: (At 10,500’)

It looks like the unstable air mass that caused this storm has, well, stabilized.  Another strong low-pressure system building off of southern California could start sending some moisture our way tonight.  This low will continue to bring moist and unstable air through the area all week, causing some spotty precipitation.

Monday:  Scattered clouds with a 20% chance of isolated snow showers.  Highs 35 to 45.  Winds shifting to the South at 10 to 15 mph.
Monday night: Cloudy with a 50% chance of snow.  Lows in the 20s.  Southeast winds 10 to 15 mph
Tuesday: 60% chance of snow with 1 to 3 inches of accumulation.  Highs 35 to 45.  Southwest winds 10 to 15 mph.
 

Avalanche Conditions:

Well, the storm has abated and left us with more than 12” of new snow.  The wind, however, just keeps on blowing and piling snow onto those leeward slopes.  On the North through East slopes the rain crust (below 11,000’), the dense snow over light snow boundary, and the buried surface hoar layer still persist below this new snow. On the Western and Southerly slopes there is a weak but slippery sun crust below all of this new snow, and a few thin layers below that there is another slippery crust left over from our long high pressure at the end of January.  The stress that the new snow has put on these layers worries me.  The snow pack is on the cusp of failure; it is just waiting for a trigger (like us).  On the wind loaded slopes (mostly those North through East aspects) there is even more stress making those slopes even closer to failure.  The wind slabs are thick, stiff, and able to transmit force across large areas of the snow pack.  They break very quickly and cleanly and without much warning.  With all of this wind, slopes and areas that might not normally be wind affected will be loaded.  There are pockets of wind slab in the trees, hiding behind features on SW, and on cross-loaded slopes.  You could easily trigger a slide in these small unexpected wind slabs that would propagate out onto a larger slope.  Be aware and try to identify those tricky wind loaded areas; look for ripples in the snow, a random cornice in the trees (I did see a 3’ cornice well into a treed slope yesterday and when I kicked it off, the steeper slope below it failed!), riming on the trees, or any other signs of wind loading.  I was able to trigger small slides on most of my test slopes yesterday with minimal work.  One of them failed with a pole plant!  I heard widespread whumphs, and felt the snow pack collapse beneath my skis several times. I also saw a natural slide on the backside of Julie’s Glade.  It was on a 36 degree slope facing NE.  The Crown was about 40’ wide and like most of my test slopes it failed first in the new snow/wind slab and then stepped down to the older weak layers below.  I would expect to see both natural and human triggered slides exhibit more of this pattern and start with a failure in the wind slabs or new snow and step down to our underlying weak layers.  Be observant and alert!  Look for those signs of instability (avalanche activity, cracking under your skis, whumphing, collapsing, cracks in the slope, wind loading, signs of wind, etc.), and when you see them, pay attention. 

Again, I would try to ski lower angled, sheltered, treed slopes and ridgelines today.  Those North thru East aspects that are wind loaded are going to be scary!  Be aware of trigger points (places where we are more likely to cause failures in the weak layers) like steep convex rollovers, shallow rock outcroppings (where a skiers weight can transfer energy deeper into the snow pack), trees, and tender cornices on any slope.

The Bottom Line for today:  An avalanche danger of CONSIDERABLE with pockets of HIGH in the steeper  wind loaded areas (especially those North through East aspects) on all aspects at all elevations. 

 

 

Nordic and Skate Skiing:

There is a classic track set into Gold Basin and up to Geyser Pass.