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 well 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 Julies 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.