Glacier Country Avalanche Center

• --Rocky Mtn. Outfitter, 135 Main Street, Kalispell
• --The Sportsman and Ski Haus in both Kalispell and Whitefish
• --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
• --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
 
We thank Pady and Pete for their recent snow reports from Marias Pass and Jewel and Kimmerly Basins.  You too can leave your snow, avalanche, and accident observations, comments, or questions at gcac@digisys.net.

This week our region began to see more seasonable weather conditions, particularly in air temperatures .  Temps generally cooled this week over the entire area with mountain daytime highs of 20-25 F common.  Nighttime lows were often around the mid teens.

New snowfall amounts were only “dribs and drabs” and in a normal year these would hardly have caused notice.  But in this year of far below normal storm activity, even light, scattered snow showers are events of notice.

Winds west of the Divide have mostly been light to non-existent.  Along and east of the Continental Divide however, strong, generally S-SW’erly winds have been blowing since Tuesday.  These were transporting snow from windward slopes and redepositing onto leeward ones.

Our observations and the reports that we received this week were generally finding a snowpack with appreciable strength.  Our observations on Thursday were in the Many Glacier Valley, at Noisy Basin in the Swan Range, and at Scenery Mountain in the northern Cabinet Range on the Kootenai.  We had reports earlier in the week from Marias Pass on the Divide, Kimmerly Basin in the southern Whitefish Range, and Noisy Basin in the Swan.

On Tuesday Pady was reporting very unstable conditions in the Marias Pass area.  Cold temps and significant wind loading was creating at that time soft to hard wind slab instability on steep east facing slopes.  Her party was able to trigger slides on these slopes as they traveled at some distance away on the corniced ridges.  These 12” deep slides were easily sliding into timber lower on the slopes.  Pady felt they posed a serious trauma threat to travelers there on Tuesday.

Our observations and reports elsewhere and later in the week, were not finding this degree of instability.  The weaknesses that early season existed at the base of the region’s snowpack continue to settle and strengthen as the snowpack grows in depth.  This layer is becoming insulated from the colder air temperatures at the surface.  Mid layers continue to display their dominating strength.  The most significant weaknesses appear to be near the surface.  These are associated with the recent new snowfall and wind deposited snow.  Cold air temperatures for at least part of the day are keeping the surface snow loose and weakly bonded.  Wind compaction in some areas is the major densifying force at work..

Below 5500’ in elevation we are finding that the snowpack is generally stable with only isolated areas of instability.  Natural avalanches are very unlikely there, while human triggered avalanches are unlikely.  Shallow snowpacks coupled with abundant anchoring generally makes backcountry travel safe there.  Normal caution however is always advised.

Above 5500’ a higher level of snow instability continues to exist.  Unstable slab layers remain possible on steep, open slopes there.  Natural avalanches are unlikely, but human triggered avalanches are possible.  The two main areas of concern we have here relate to the weakly bonded layer at the base of the snowpack, particularly in the more shallow snow covers, and with the slab potential at the surface in areas that recently received significant deposits of wind transported snow.  These are of particular concern along and east of the Continental Divide.  Recent nighttime cold temperatures could have also weakened the bond between mid-pack to near-surface layers.

The weather forecast this weekend is for a progression of weakening upper level disturbances bringing scattered, light accumulations of new snow to the region.  Weak westerly flows aloft on Friday and Sunday will be separated by a weak upper ridge of drier air on Saturday.

On Friday we expect mostly cloudy conditions with scattered light snow.  New snowfall in the mountains on Friday should be 1-2”.  Daytime high temperatures are forecasted to be in the low 20’s F, with mountaintop winds W’erly 10-20 MPH.

Saturday morning light, isolated, orographic snow showers should linger as  moist air lifts over our N-S oriented mountain ranges.  By afternoon drier air is expected to pressed into the region by a weak upper ridge of higher pressure.  Mountain daytime highs should remain in the low 20’s.  Mountaintop winds are still forecasted to be W’erly, but dropping slightly from Friday to 5-10 MPH.

Sunday should continue cloudy with scattered light snow showers redeveloping.  New snowfall amounts in the mountains are expected to be another 1-2”, with mountaintop winds W’erly 10-20 MPH, and mountain daytime high temperatures still in the low 20’s F.

These conditions should keep the snow stability and avalanche danger in limbo this weekend.  We don’t expect any dramatic changes in the stress side of the stability equation.  Scattered light snow showers will not significantly load the snowpack.  Light to moderate wind activity would be the most concern in areas where conditions did produce wind transport and redeposit of snow.

Nor do we expect a significant change in the strength side of the stability equation.  Seasonable temperatures with at least significant cooling at night should maintain the surface layers of the snowpack cold and weakly bonded.

Backcountry travelers will need to remain alert to varying snow instability.

Next week the avalanche center and David Thompson Search and Rescue will be offering a public Level II Avalanche Awareness training session in Libby.  The lecture series portion of this program will be held Thursday and Friday, January 25&26 at the David Thompson SAR “barn” between 3rd & 4th Streets, starting at 7 PM.  The all-day field session on Saturday, January 27, will be at Turner Mountain.  A prerequisite for this program is a prior completion of a Level I Avalanche Awareness course.  More information can be obtained by calling Jon Jeresek at 293-8246 or Terry Crooks at 293-6629.

Flathead Valley & Outside Montana  -- 406-257-8402

Toll-free Within Montana -- 1-800-526-5329

In an effort to improve our service to the public we are attempting to define the users of this advisory message. Please e-mail us a message at gcac@digisys.net with a message listing your backcountry interests. Are you a snowmobiler, snowboarder, mountaineer, snowshoer, or skier? Also let us know where you reside.
 

Thank you for your continuing support of Northwestern Montana's Glacier Country Avalanche Center.
 

MODERATE DANGER ...unstable slab layers are possibleon steep terrain. Natural avalanches are unlikely, while human triggered avalanches are possible. Backcountry travelers should use caution in steeper terrain on certain aspects.

CONSIDERABLE DANGER ...unstable slab layers are probableon steep terrain. Natural avalanches are possible, while human triggered avalanches are probable. Backcountry travelers should be very cautious in steeper terrain. Be aware of potentially dangerous areas of unstable snow.

HIGH DANGER ...unstable slab layers are likely on a variety of aspects and slope angles. Both natural and human triggered avalanches are likely. Travel in avalanche terrain is not recommended. Safest travel is on windward ridges or on lower angle slopes without steeper terrain above.

EXTREME DANGER ...extremely unstable slab layers exist on most aspects and slope angles. Widespread natural and human triggered avalanches are certain . Large destructive avalanches are possible. Travel in avalanche terrain should be avoided and travel confined to low angle terrain well away from avalanche path runouts.