NW MONTANA GCAC BACKCOUNTRY AVALANCHE ADVISORY 2-28-97 This is Stan Bones with the Backcountry Avalanche Advisory for the Glacier Park and Flathead and Kootenai National Forest areas issued at 10:30 AM, Friday, February 28th, 1997, by Northwestern Montana's Glacier Country Avalanche Center. This advisory does not apply to developed ski areas and is brought to you in part by financial grants from: --Adventure & Glacier Motor Sports in Columbia Falls --Winter Sports, Inc. of Whitefish --The Aero Inn, Highway 93 South, Kalispell --Ski Mountain Sports in Whitefish --The Flathead Nordic Ski Patrol --Rocky Mtn. Outfitter, 135 Main Street, Kalispell --The Izaak Walton Inn located at Essex --The Runner-Up Sports Consignment Shop in downtown Whitefish --The Users and Supporters of the Glacier Country Avalanche Center --The Montana Department of Fish, Wildlife, and Parks For those of you accessing this message from within the Flathead Valley we remind you of the cheaper local access number of 257-8402. We would appreciate hearing from you. After the beep please leave your suggestions for improvement of this message and your snow, avalanche and accident observations. Names need not be given. At any time you can go directly to the beep by pressing *. In your message please include the time and date of your call. By computer we can be reached at the e-mail address of gcac@digisys.net. The avalanche danger is currently being rated as MODERATE-TO-HIGH on slopes steeper than 35 degrees that have received significant deposits of new snow loading from either precipitation or wind loading. The danger on all other slopes is rated MODERATE. ******************************************************* WEATHER & SNOWPACK ANALYSIS For the last three days Northwestern Montana has experienced a moist Pacific weather flow. This was capped on Wednesday night with a fast moving front that brought heavy snowfall to portions of our region. The strongest hit area appears to have been the moisture favored southern Whitefish and Northern Swan Ranges. Noisy Basin near Bigfork picked up nearly 3" of snow-water-equivalent in 15 hours Wednesday night. This translates into 20 inches of new snowfall. The southern Whitefish Range received approx. 12" of new snow, while Poorman Basin in the Cabinets near Libby picked up 7". Marias Pass, along the southern edge of Glacier Park, likewise had around 7" of new snow. This new snowfall was accompanied by variable winds. Our reports and observations were that speeds and directions were all over the map, with the strongest being through the Continental Divide passes and in the wind favored canyons west of the Divide. Wind direction on Marias Pass was reported to be from the east on Thursday, while Big Mtn was generally experiencing northerly winds. In the Cabinet and Swan Ranges winds were generally more light and variable. Snowpit investigations Thursday were finding considerable weaknesses associated with the new snowfall. Natural and artificial avalanches in the southern Whitefish Range Thursday were generally wind loaded slabs failing upon buried graupel and buried surface hoar and angular grain layers. These slides frequently had step fractures indicating that the initially failing weakness was higher in the snowpack, but as the moving snow would generate more energy and weight, a second or third more deeply buried weak layer would release. ******************************************************* AVALANCHE - INSTABILITY ADVISORY On wind sheltered slopes we are currently rating the avalanche danger as MODERATE. Unstable slab layers are possible on terrain steeper than 35 degrees. Natural avalanches are unlikely, while human triggered avalanches are possible. Backcountry travelers should use caution in steeper terrain on all aspects. Recent new snowfall is adding weight to the stress side of the snow stability equation on many of these slopes and the bonding between the new snowfall and buried bed layers tends to be weak in most locations. On wind deposited slopes we are rating the avalanche danger as being MODERATE-TO HIGH. Here the stress of rapid wind loading of snow is causing instability and unstable slab layers are probable. Natural avalanches are possible, while human triggered avalanches are probable. Travel in avalanche terrain receiving significant deposits of wind transported snow is not recommended. Safest travel is on windward ridges or on lower angle slopes without steeper terrain above. Backcountry tourers should avoid travel on or beneath wind deposited slopes steeper than 35 degrees. Tourers should also be aware that as one climbs higher the thickness and strengths of buried melt-freeze ice layers is less. This means that a greater potential exists for slab releases to occur on weak layers deeper than the newfallen surface snow layer. ******************************************************* WEATHER FORECAST & AVALANCHE OUTLOOK It appears that more weather is on the way. On Friday weak disturbances should move through the areas in a northwest flow and keep some scattered snow showers over us. On Saturday a developing low pressure system in the Gulf of Alaska should push a warm front toward us with a cold front to follow Saturday night. This system is expected to bring more significant snows to our region over the weekend. Temperatures are forecasted to remain mild to cool with mountain highs generally in the 20's cooling to the teens by Sunday. Less than 1" of new snow is expected Friday, however Saturday could see 6-10" of new snowfall in the mountains. Freezing levels should be their highest Saturday at around 4500' in elevation. The new snow is expected to be accompanied by 30-40 MPH SW winds. There is plenty of loose snow available in most all locations for wind transport. New snowfall coupled with moderate to strong winds and generally cool temperatures should keep the avalanche danger elevated this weekend. When traveling in the backcountry pay attention to the wind. Avoid travel on or beneath wind loaded slopes this weekend. Even on wind sheltered slopes steeper than 35 degrees stop and check the bonding of the new snow to last Sunday and Monday's surface crust. As you climb higher check the strength of the more deeply buried melt-freeze layers. There is some good powder skiing, boarding, and snowmobiling in the backcountry currently and it sounds like more is on the way. But there are also significant weaknesses within the snowpack that could turn an exhilarating run with friends into a tragedy. Check it out before jumping in or ripping up and always expose only one person to a potential avalanche risk at a time while the remainder of the party watches from safe locations. Always carry and know how to use avalanche transceiver, probes, shovels, and first aid kits. ******************************************************************* This concludes the current avalanche advisory. Because of other commitments the next regularly scheduled update will be issued at 9:30 AM, Monday, March 3rd, 1997 or earlier if conditions warrant. For those of you with access to the World Wide Web, check out this and other avalanche advisories at www.csac.org and at www.avalanche.org. ******************************************************************* In an effort to improve our service to the public we are attempting to define the users of this advisory message. Please stay on the line until after the beep and leave a message listing your backcountry interests. Are you a snowmobiler, snowboarder, mountaineer, snowshoer, or skier? Also let us know if you are calling from within the Flathead access area or outside and using the 1-800 number. 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 a transition zone between hazards exist. Because of the general nature of the advisory, each backcountry party will always need to make their own site and time specific avalanche hazard evaluations. For current information on snow conditions stop at the Glacier Park Ranger Station at your point of entry, or call a U.S. Forest Service Office. Thank you for your support of Northwestern Montana's Glacier Country Avalanche Center. ************************************************************