January 14, 2014 Avalanche Advisory
The avalanche danger is CONSIDERABLE on slopes steeper than 35 degrees. High winds and heavy snowfall have formed dangerous wind and storm snow slabs on steep terrain above 6000 feet. Natural avalanches are possible and human-triggered avalanche are likely in these areas.
The avalanche danger is MODERATE at all other locations and elevations. Natural avalanches are unlikely but human-triggered avalanches are possible on all other slopes steeper than 35 degrees due to the heavy snowfall and high wind west central Montana experienced in the past 3-4 days.
Good morning! This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday, January 14, 2014. This information is the responsibility of the Forest Service and does not apply to operating ski areas. The danger rating expires at midnight tonight.
Weather and Snowpack
Heavy snow and high winds this past weekend increased the avalanche danger prompting the first avalanche warning of the season. All locations including the southern Bitterroot mountains near Lost Trail Pass received nearly 30 inches of storm snow with winds gusting into the 50 mph range during this period. Twin Lake, Lolo Pass, Hoodoo and North Fork Jocko SNOTEL stations recorded 2.5 to over 3 inches of SWE from Friday to Monday.
This morning, mountain temperatures are in the thirties and SNOTEL stations picked up about 2 inches of snow overnight. Wind speeds at the Point Six and Deer Mountain RAWS stations are in the 40-50 mph range.
On Monday, avalanche specialists were in the Hoodoo Pass, Rattlesnake Wilderness and southern Swan range near Seeley Lake. Each site was experiencing high winds and heavy snowfall Monday making travel difficult and visibility poor.
At each of these locations, the primary avalanche problem is wind slab development on any steep lee aspect. The character of the high winds of the past few days makes assessment of this slab tricky. Many places can be wind loaded further down slope and more terrain cross loaded than is typical under these high wind events.
The secondary avalanche problem is storm snow slabs. The snow of the past 3 days was deposited on a weaker layer of snow and a thin layer of facets that formed during the last clear weather we had last week. While the new snow appears to be bonding well to the older snow surface, many of the stability tests were showing failures at this interface. See the pit profiles here.
The southern Swan did not receive as much new snow as other areas but the winds were strong here as well so wind slab formation is the primary concern. The newest snow had not yet formed a slab but was sloughing easily on slopes steeper than 40 degrees.
The more deeply buried facets near the ground show up in some of our pits mainly in the shallower snow packs or near rocky areas. The location of this weak condition is highly variable so the only way to know for sure is to dig down into the snow.
Weather and Avalanche Forecast
We can finally report that after today, the wind should not be a factor. The backcountry weather forecast issued by the Missoula National Weather Service Office indicates a relaxing of the wind as high pressure builds over the region during the next few days. Valley inversions will strengthen and mountain temperatures will rise into the 40’s by Saturday.
I expect to see the snowpack to continue adjusting to the heavy load it received over the past few days. It will also gain strength with the moderate temperatures in the forecast. We can also expect to see another crop of surface hoar and near surface facets develop during this clear weather which may be an issue after the next storm.
Dudley Improta will issue the next advisory on Friday, January 17.
Thanks to the folks at Bitterroot Brewery, the businesses who donated raffle items and to everyone who came out to support us at last Friday’s benefit in Hamilton. It was a big success and a ton of fun! THANK YOU!
