07/01/26_advisory
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 6th for the Glacier Park and Flathead and Kootenai
National Forest areas.
HAZARD ANALYSIS
Between 5000
and 7500 feet of elevation, the avalanche danger is currently being
rated as LOW during periods of freezing and MODERATE during times of
thaw. Below
5000 feet of elevation, the avalanche danger is currently being rated
as
LOW.
These danger
ratings expire at midnight, Friday, April 6th.
The outlook is for the avalanche danger to remain near current levels
through the 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:
New snowfall
was received over the region Saturday night and again Monday
night. Snow water equivalent gains were variable with Noisy
receiving the most early Sunday with 1.1 inches of SWE. Flattop
was even more interesting with a gain of only .5 inches of SWE but
delivered when temperatures were in the teens gaining close to 9 inches
of snow on Monday. The melt-freeze
cycle continues with colder nighttime temps favorably influencing the snowpack from
Sunday through Wednesday. A slight warming trend on Thursday was
experienced but cooler temperatures returned overnight.
SNOWPACK
ANALYSIS:
Our backcountry
observations Thursday were from Kimmerly Basin on
the Flathead National Forest and from Benning Mountain in the West
Cabinet
Range on the
Kootenai National Forest.
Thursday
the snowpack was nearly isothermal. New snow Sunday through
Tuesday, depending on the local, was sitting over a graupel layer which
was sensitive to failure. This graupel layer, will likely modify
with the warming temperatures expected this weekend. Melt freeze
crusts increased in strength, with the colder temperatures. There are some slab
layers with thin weak interfaces still maintained deep into the
pack These weak interfaces along with bedrock surfaces could
react with significant warming and or a rain event.
AVALANCHE -
INSTABILITY DESCRIPTION:
Between
5000 and 7500 feet in elevation
we are currently rating the avalanche danger as LOW during periods of
freezing conditions. Melt freeze ice at or near the surface is
providing strong bridging over underlying weaker layers.
During the times of freezing conditions the snowpack 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. During times of freeze watch for
any accumulations of new snow overlying near surface ice crusts.
During
periods of thaw, the avalanche danger is rated as MODERATE between 5000
and 7500 feet in elevation. With warming and surface weakening,
unstable near surface snow and more deeply buried weaknesses are
possible. Natural avalanches are unlikely, while human triggered
avalanches are possible. Backcountry travelers should use caution in
steeper terrain on certain aspects. Watch for both loose
instability above the melt freeze ice layers and slab instability
deeper in the pack if the strength of the near surface ice erodes
during periods of thaw.
Below 5000 feet of
elevation the avalanche danger is currently being rated as LOW...
snow 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:
`
Current Western Montana National Weather Service Backcountry Weather
Forecast
High Pressure
at the surface and aloft will make for mainly dry conditions across the
Northern Rockies through Saturday. East winds influenced by a
surface high to the east will blow over the region the next couple of
days. These winds will also drive a few light upslope showers
over Glacier National Park. Temperatures will rise under the
ridge. Sunday the ridge will further amplify making for warmer
temperatures.
Warming
temperatures, thaw, will signal potential instability on big open solar
influenced terrain. Avoid this type of terrain during periods of
thaw. Avoid wandering too close to cornice ridges as the
freezing
levels climb which will only weaken the large cornices. The large
cornices can fall with great force and could potentially trigger a
slide below these over hangs.
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.
This is the
last advisory for the 2006/2007 winter season. GCAC will again be
open for business in December of 2007. Thank you for your
support.
This message is
available via telephone at 257-8402 or on the internet
at www.glacieravalanche.org
Report from:
Glacier Country Avalanche Center
Glacier