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)
If you would like to get the bulletins by e-mail automatically as
they are issued you can subscribe
to our mailing list.
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.
SUBSCRIBE! and receive these bulletins automatically by email.
Hazard Scale - [PDF Full Size] [PDF Pocket Reference]
 |
www.avalanche-center.org |
 |
|