This message does not apply to developed ski areas and is brought to you in part by financial grants from GCAC Sponsors
INTRODUCTION:
This is Tony Willits with the backcountry avalanche advisory issued by the U.S. Forest Service Glacier Country Avalanche Center at 8:00 AM, Tuesday, March 9th for Glacier Park, Flathead and Kootenai National Forest areas.
HAZARD ANALYSIS
The avalanche danger between the elevations of 5,000 and 7,500 ft. is currently being rated MODERATE on all large, steep, open slopes lacking vegetative and terrain anchors. On anchored slopes below 7,500 ft. and all slopes and aspects below 5000 ft., we are rating the avalanche danger as LOW.
These danger ratings expire at midnight, Tuesday, March 9th. The outlook is for the avalanche danger to remain at current levels through Wednesday although Thursday could have increased avalanche hazard during the day with the return of high pressure and potential thawing during peak solar warming.
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.
WEATHER ANALYSIS:
New snow accumulations since 2100 hours last night, resulted in .2 to .5 of a snow water equivalent increase which equated to 3 to 6 inches of new accumulation. Winds were light on Monday with daytime temps just above freezing up to 7,500 ft. elevation.
SNOWPACK ANALYSIS:
Our backcountry observations on Monday, were from Noisy Basin on the Flathead National Forest and from Garden Ridge in the Purcells on the Kootenai National Forest.
No new slab activity was noted or was reported on Monday. Snowpack was isothermal from surface to ground with mostly cloudy conditions overhead. Thawing over Saturday and Sunday produced free water within the snowpack but percolation channels had refrozen overnight Sunday. Stress tests revealed some clean shear planes but required a very hard force to release. Although extended column tests were resulting in propagation down about 50 cms across the column and still is a concern in some locations. Solar aspects were very firm.
AVALANCHE - INSTABILITY DESCRIPTION:
We're currently rating the avalanche danger between the elevations of 5,000 and 7,500 ft. as MODERATE on all large, steep, open slopes lacking vegetative and terrain anchors. Unstable deep slab layers are possible. Natural avalanches are unlikely, but human triggered avalanches are possible. Backcountry travelers should use caution in big, steep, open terrain on all aspects.
On anchored slopes below 7,500 ft. and all slopes, all aspects, below 5,000 ft., we're rating the avalanche danger as LOW. The shallow snow there is generally stable with only isolated areas of instability. Natural avalanches are very unlikely, while human triggered avalanches are unlikely. Backcountry travel is generally safe. Normal caution is advised.
WEATHER FORECAST & AVALANCHE OUTLOOK:
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Current Western Montana NWS Backcountry Weather Forecast.
A cold Pacific Trough of low pressure will impact the region today. A split flow will once again develop Wednesday as most of the energy from the next Pacific weather system dives into the Great Basin. High pressure is expected to return Thursday and Friday.
Backcountry travelers need to realize that LOW avalanche danger is not the same as NO avalanche danger. The prolonged periods of daytime thawing coupled with overnight refreezing drives the likely hood/probability of triggering avalanches lower although the results of triggering an avalanche could have some ugly consequences with weak interfaces lingering from a depth of 40 to 50 cms below the surface. This could transfer into a situation of if buried consequences could be high for injury or worse.
Please note that this avalanche advisory is our best interpretation of snow pack conditions and National Weather Service Forecasts on the day the advisory is issued. Unanticipated weather changes such as wind, a marked temperature increase, or precipitation beyond forecast amounts can increase the avalanche danger. Local variations may also exist.
The next avalanche advisory will be on Friday, March 12th, 2010.
This message is available via telephone at 257-8402 or on the internet at www.glacieravalanche.org
DANGER RATING KEY
This advisory is also available on telephone hotline by calling:
Flathead Valley & Outside Montana -- 406-257-8402
Toll-free Within Montana -- 1-800-526-5329
Report your avalanche observations and incidents here
In an effort to improve our service to the public we are attempting
to define the users of this advisory message. Please contact us
with a message listing your backcountry interests. Are you a snowmobiler,
snowboarder, mountaineer, snowshoer, or skier? Also let us know
where you reside.
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.
Thank you for your continuing support of Northwestern Montana's Glacier
Country Avalanche Center.
