NW MONTANA GCAC BACKCOUNTRY AVALANCHE INFORMATION 12-15-00 This is Stan Bones with Backcountry Avalanche Information for the Glacier Park and Flathead and Kootenai National Forest areas issued at 10:00 AM, Friday, December 15th, 2000, by Northwestern Montana's Glacier Country Avalanche Center. This message does not apply to developed ski areas and is brought to you in part by financial grants and support from: --Winter Sports, Inc. on The Big Mountain --The Aero Inn, Highway 93 South, Kalispell --The Izaak Walton Inn located at Essex --Kalispell Regional Medical Center --Rocky Mtn. Outfitter, 135 Main Street, Kalispell. --The Sportsman and Ski Haus in both Kalispell and Whitefish --Burlington Northern Santa Fe Railroad --The Flathead Nordic Ski Patrol --The Montana Department of Fish, Wildlife, and Parks --The National Forest Foundation --The Users and Supporters of the Glacier Country Avalanche Center ******************************************************* Because of new snowfall accompanied by warming temperatures and often by strong, gusty SW and W winds we are currently rating the avalanche danger over Northwestern Montana to be HIGH on steep open slopes lacking vegetative anchors. ******************************************************* WEATHER ANALYSIS Following upon the heels of last weekend's arctic front a strong, surface, low pressure system began to move over Northwestern Montana Thursday night. This system brought with it increasing temperatures, locally heavy snowfall, and occasional strong SW and W'erly winds. Low temperatures Thursday morning at many mountains locations were in the teens. Daytime highs in the northern half of our region warmed pretty much into the high teens during the day Thursday, while in the southern half they warmed into the mid 20's. By Thursday night most night time low temperatures in both halves were in the low to mid 20's. By Friday morning many locations over our region, particularly in the southern half, were beginning to experience strong gusty winds. Gust speeds around Flathead Lake were near 30 MPH from the SW Friday morning. At St Mary N'erly winds were gusting into the 20's. Thursday night and Friday morning most all mountains locations received significant amounts of new snowfall. Stations like Flattop in Glacier Park, Noisy Basin near Bigfork, North Fork Jocko at the southern end of the Mission Range, and Bear Mtn on the Idaho border, that typically receive big precipitation, all registered at least 1" of SWE Thursday night and Friday morning. Drier sites received at least 0.5" of SWE. ******************************************************* SNOWPACK ANALYSIS Our backcountry tours on Thursday were continuing to find a very loose, weak snowpack over our entire region. Cold temperatures had weakened the early season snowpack, transforming it into a layer of weakly bonded grains at best, totally cohesionless at worst. Continuing cold temperatures this past week insured that any new snowfall received was light and fluffy. So on Thursday even in snowpacks of 2-3' boot penetration still was often completely to the ground. Ski, board, and snowmobile flotation was hardly better. This loose, cold snowpack was the base that Thursday night's new snow began to be deposited upon. Warming temperatures and strong winds are guaranteed to have created an inverted snowpack with heavier, more dense snow upon a deep base of weak, loose snow. Wind deposited snow almost always forms into cohesive slabs on leeward slopes. These slabs are expected to have captured beneath them layers of loosely, poorly bonded snow. ******************************************************* AVALANCHE - INSTABILITY DESCRIPTION Because of the significant amounts of new snowfall Thursday night accompanied by warming temperatures and often strong winds we are currently rating the avalanche danger on steep open slopes as HIGH. Unstable surface slab layers are likely overlying a base of colder, weakly bonded snow. Both natural and human triggered avalanches are likely on slopes lacking vegetative anchors. Travel in avalanche terrain is not recommended. Safest travel is on windward ridges or on lower angle slopes without steeper terrain above. ******************************************************* WEATHER FORECAST & AVALANCHE OUTLOOK The weather forecast is for more potent weather systems to move over Northwestern Montana through the weekend. Warming temperatures are expected through Saturday. Saturday night a trailing cold front is forecasted to produce a cooling trend. Through out the weekend the forecast is for mountain and valley snow. New snowfall of 14-20" is expected in the mountains Friday, with 12-18" additional Saturday, and 8-12" more on Sunday. Valley snowfall is expected to be just slightly less. Ridge-top winds Friday and Saturday should be from the W at 40-50 MPH. These strong winds are forecasted to continue Sunday when they shift more to the NW. Night time temperatures should remain below freezing through the period, with day time highs reaching near freezing in the lower valleys on Saturday. On Sunday temperatures are expected to begin another cooling trend. Mountain day time highs Friday should be in the lower teens, warming to the upper 20's on Saturday, and dropping to the upper teens on Sunday. These combinations of additional significant snowfall, warming temperatures, particularly on Saturday, and consistently strong winds should keep the avalanche danger and snow instability at elevated levels during the period. Backcountry travelers should keep their tours this weekend to avalanche safe routes. Let the snow settle and strengthen before venturing onto hazardous terrain. Out of this event will come better conditions as we begin to build a genuine base to the snowpack, but this weekend is probably a good time to finish up your Christmas shopping. ******************************************************************* This concludes the current avalanche message. The next regularly scheduled update will be issued by 11:00 AM, Tuesday, December 19th, 2000. ******************************************************************* In January the avalanche center will again be offering its public avalanche awareness training session. This program consists of a 4-night lecture series held at the Summit Health and Fitness Center in Kalispell on the evenings of Mondays and Wednesdays, January 8,10,15,&17, 6:30-9:30 PM. These will be augmented by field days on Saturdays, January 13&20. More information can be obtained about these sessions by calling me Stan Bones at 758-5284 during the day or 837-6022 evenings. ******************************************************************* This message 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 message, each backcountry party will always need to make their own site and time specific avalanche hazard evaluations. Thank you again for your continuing support of Northwestern Montana's Glacier Country Avalanche Center. ************************************************************