Glacier Country Avalanche Center Advisory (Northwestern Montana)

NW Montana Avalanche Bulletin

This version brought to you by The CSAC Avalanche Center, http://www.avalanche-center.org/

The following Bulletin is from the Glacier Country Avalanche Center (GCAC)

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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, Friday, April 10th for Glacier Park, Flathead and Kootenai National Forest areas. This will be the last regular advisory issued for the 2008-2009 season. Only special advisories as warranted, will be issued for the remainder of the spring.

Hazard Analysis

Between 5000 and 7500 feet of elevation on steep open slopes (greater than 30 degrees) the avalanche danger is currently being rated as

during periods of thaw and as

during periods of freezing. Below 5000 feet of elevation the avalanche danger is currently being rated as

These danger ratings expire at midnight, Friday, April 10th. The avalanche hazard is expected remain at the current level through this weekend. 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

Only a trace of new snow since last Friday and since Tuesday almost no refreezing has occurred, at least anything significant, in terms of seizing up the surface snowpack.

Snowpack Analysis

Our backcountry observations Thursday were from Noisy Basin on the Flathead National Forest and Poorman Drainage in the East Cabinets on the Kootenai National Forest. Since Monday thawing and settlement has been ongoing in the regions snowpack. Wet slab activity was observed in Noisy Basin and as well from the Kootenai observation. With the sustained warming this past several days intense roller ball activity led into point releases and small wet slabs especially on south and west aspects. A 16 to 18 inch slab pulled out over a melt freeze layer on an east aspect in Noisy Basin and north aspects with wet slab activity in Poorman. Ice layers were still bridging softening mid pack layers and stress tests were revealing those being the best bed surfaces to slide upon, with less than snappy shears.

Avalanche - Instability Description

During periods of thaw, between 5,000 and 7,500 ft. elevation we're rating the avalanche danger as where unstable slab layers are probable on 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. During periods of freezing, between 5,000 and 7,500 ft. elevation we're rating the avalanche danger as where unstable slab layers are possible on steep terrain. Natural avalanches are unlikely, while human triggered avalanches are possible. Backcountry travelers should use caution in steeper terrain on all aspects. Below 5,000' elevation we rate the avalanche danger as 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

` A weak and complex pattern will be present over the region during the next several days. Snow levels will be quite high during much of this time, with temperatures near the seasonal average. Shower activity will reenter the region during Friday afternoon however no significant snow events are anticipated during the forecast period.

Snowmobilers will need to be extra cautious during periods of thaw to avoid being a trigger. Climbing on steep terrain with a soft surface snowpack especially over or near shallow packs (like buried rock bands) could trigger deeper into the pack even below the mid pack elevations. The weaker basal layers are still lingering from our early cold in December and although decomposing from the prominent sugary crystals they are still a potential to consider especially with aggressive hill climbing. As an example, was one such second hand report of a snowmo incident climbing below a cornice and triggering a slide down to rock and bear grass.

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.

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