Avalanche advisory does not apply to developed ski areas

Issue Date: 6:30 AM, Friday, January 20, 2012 This advisory is a product of the US Forest Service, US Dept. of Agriculture. Along with other snow and avalanche information, it is originally posted Valid Until: Midnight, Friday, January 20, 2012 at http://www.fs.usda.gov/flathead. An audio summary is available via Next Update: Tuesday, January 24, 2012 telephone at 406-257-8402 Issued by: Stan Bones

All Mountain Ranges

Avalanche Danger Summary 7,500 ft. elevation 3 -Considerable : 5,500 to 7,500 ft. elevation on steep, open terrain 5,000 ft. elevation 2 - Mod : below 5,500

AVALANCHE – INSTABILITY DESCRIPTION All Mountain Ranges - 5,500 to 7,500 ft. elevation Danger Level 3 – CONSIDERABLE Confidence Good Dangerous avalanche conditions exist Travel Advice Careful snowpack evaluation, cautious routefinding, and conservative decision-making essential Natural avalanches possible Likelihood of Avalanches Human triggered avalanches likely Small avalanches in many locations or Avalanche Size & Distribution Large avalanches in specific areas or Very large avalanches in isolated areas

AVALANCHE – INSTABILITY DESCRIPTION All Mountain Ranges – below 5,500 ft. elevation Danger Level 2 - MODERATE Confidence Good Heightened avalanche conditions on steep, open slopes and gullies Travel Advice Evaluate snow and terrain carefully Identify features of concern Natural avalanche unlikely Likelihood of Avalanches Human triggered avalanches possible Small avalanches in specific areas or Avalanche Size & Distribution Larger avalanches in isolated areas Concern is steep, open slopes and gullies lacking vegetative and terrain anchors Because of the general nature of this advisory message, each backcountry party will always need to make their own time and site specific avalanche hazard evaluations. This advisory best describes conditions at the time of its issuance. As time passes avalanche and snow conditions may change, sometimes quite rapidly. Elevation and geographic distinctions used are approximate and transition zones between hazards exist.

Recent Mountain Weather Tuesday –Thursday ---A robust westerly flow of moist Pacific air collided with a Summary cold air mass sagging south from Canada Both mountain and valley locations received significant amounts of new snowfall – the biggest storm of the season to date S’ern Mission Range received the most (2.5 to 3.0+ inches of snow water Precipitation equivalent over the three days of Tuesday through Thursday Remaining mountain locations received lesser amounts (1 to 2 inches of snow water equivalent) Rocky Mtn Front and Continental Divide Passes - subjected to sub-zero and single digit temps F during the period West of the Divide – temperatures warmer Temperature o Wednesday was coldest day (single digits to low teens F, northern tier locations along the Canadian border being the coldest) o Thursday saw warming (high teens and low 20’s F) as the cold air mass began retreating eastward Winds have been highly variable both in intensity and direction Wind Thursday was generally calm to light

Field Observation Locations Scenery Mountain, East Cabinet Range, W of Libby Thursday, 1-19-12 Skookoleel -Smokey Ridge , S’ern Whitefish Range, N of Whitefish Noisy Basin, N’ern Swan Range, NE of Bigfork Observer Report Locations John F Stevens Canyon, along Hwy 2, W of Marias Pass Thursday, 1-19-12 Skiumah Lake area, Flathead Range, along Hwy 2, E of West Glacier

Thursday Avalanches Observed Yes o Shallow surface slab instability observed

Instability Concern / Level of Most Less Least  Avalanche Problem Concern

Significant amounts of new snow Tuesday through Thursday (approx. 10-20 inches of new depth) New Storm Wednesday’s snowfall generally cold, low density or  Thursday’s new snow rimed and of higher density Near Surface Snow Surface layers inverted with weak buried structure attempting to support heavier surface layer Tuesday and Wednesday winds highly variable in direction and intensity Wind Loading  Thursday winds relatively calm Significant amounts of light snow available for wind transport if winds do develop Recent cold temperatures has preserved, if not enhanced, Recent preexisting weaknesses associated with buried surface hoar or Persistent Buried  layers and buried rain crusts These weak layers reacting with moderate force in shear tests Weak Layer Currently buried around mid-pack by recent new snowfall Spring Wet Snow or Not applicable Melt-Freeze Rain-on-Snow Not applicable Rapid new cold snowfall has potential to produce cohensionless Loose Snow  loose snow point release avalanches Other Concerns

Unusually shallow snowpack with significant amount of vegetative anchors, Noisy Basin, N’ern Swan Range

Steep open unanchored slopes are likely to be established avalanche start zones and paths. Remote, skier triggered, shallow, surface slab avalanche, Noisy Basin, N’ern Swan Range

Weather Forecast Current NWS Backcountry Forecast Rollercoaster waves of fast moving high pressure ridges alternating with low pressure Summary troughs through the weekend Fairly steady precipitation for the next several days Precipitation Mountain snow should linger through next week Warming to the high 20’s and low 30’s Friday night and Saturday Temperature Cooling back into the teens and 20’s Saturday night and Sunday Wind Gusty W-SW winds Saturday

Avalanche Outlook Through the weekend we expect the avalanche danger to remain elevated near Trend current levels, if not escalate Concern More snow loading /rain / wind could rapidly and dramatically increase the danger Always carry and know how to use avalanche safety equipment Watch for a possible rapid change in weather conditions beyond forecast amounts Comment Be alert that if a slope is open enough to ski or highmark currently it is very likely an established avalanche path. Check out the site specific snow stability before jumping in or on

Upcoming Events

Beginning next Monday, January 23rd Flathead National Forest will be hosting a public advanced avalanche awareness and safety workshop particularly for snowmobilers: . Four night lecture series, Mondays and Wednesdays, January 23, 25, 30, & February 1 . Two Saturday field sessions, January 28 & February 4, location and time to be announced at lecture . This is a series of lectures that builds on previous topics, participants are encouraged to attend all sessions . Free of cost . No registration, just show at the door on the north side of the building. . Flathead Nat’l Forest Supervisor’s and Tally Lake Ranger District Office . 650 Wolfpack Way … On Stillwater Rd, west of Glacier High School, and just north of Montana State DNRC office . Time for night lectures is 6:30 – 9:30 PM