Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory 
for Thursday, December 10 at 7:30 a.m.  This advisory does not apply to operating ski areas.

Mountain Weather: 

With recent temperatures dipping into negative double digits, a mere -5 degrees F seemed 
relatively warm as I walked into the office this morning.  Mountain temperatures were 
near -10 degrees F this morning except near Cooke City where they were -20 degrees F.  
Winds have been blowing 15-30 mph from the west northwest and will continue at those 
speeds today with temperatures warming to just above zero.  Since yesterday morning snow 
showers produced a trace to one inch of new snow, and today some snow may fall but will 
not accumulate.

Snowpack and Avalanche Discussion: 

The Bridger, northern Gallatin, northern Madison Ranges and mountains around Cooke City:

Yesterday Doug and I went to the northern Bridger Range spending most of our time dealing 
with a dead snowmobile battery, strong winds, and serious wind chills that had us wearing 
multiple down jackets while skinning uphill.  Near Fairy Lake we found evidence of more 
faceting in the snowpack as a result of recent cold weather, but the layer of most concern 
was buried 4-6 inches deep under snow that fell last weekend.  Currently this layer does 
not have enough stress from overlying snow to create a serious problem.  Skiers just north 
of Bridger Bowl also experienced strong westerly winds forming thick wind slabs that easily 
cracked but did not slide.

The northern Gallatin Range also has nearly three feet of supportable snow similar to that 
in the Bridger Range.  The northern Madison Range has a snowpack 2-3 feet deep with weak 
faceted snow sandwiched between denser layers.  On Tuesday the Big Sky Ski Patrol triggered 
a thick wind slab that stepped down into these faceted layers running 1500 vertical feet.  
Also on Tuesday both the Big Sky and Yellowstone Club ski patrols found surface hoar at all 
elevations.  In many places strong winds likely destroyed this potential weak layer while in 
other areas light snowfall may have preserved it.  Near Cooke City south facing slopes have 
a snowpack similar to that in the Big Sky area with layers of faceted snow sandwiched between 
crusts.  On north facing slopes near Cooke City the snowpack is deeper and a little stronger 
more like the snowpack in the Bridgers. 

Today, the primary avalanche concerns are wind slabs formed by recent west and northwest 
winds.  While these wind slabs do not appear very sensitive they are widespread and human 
triggered avalanches are possible.  For this reason the avalanche danger is rated MODERATE. 

The southern Gallatin and southern Madison Ranges, the Lionhead Area near West Yellowstone: 

Heading further south leads to a thinner snowpack which can be observed driving from Big Sky 
to West Yellowstone.  At the ground the snowpack temperature is always 32 degrees F while 
temperatures at the snow surface can be the same as air temperatures which have been as low 
as -35 degrees F leading to big temperature differences in the snowpack.  These differences 
combined with a thin snowpack create large temperature gradients that form weak faceted snow.  
This snow makes riding difficult without getting stuck, but it also makes a good recipe for 
avalanches once more snow falls.  Until then watch out for recent wind drifts that could 
fracture and slide.  For today, the avalanche danger is rated MODERATE on wind-loaded slopes 
and LOW elsewhere.