Avalanche Warning January 7, 2009

Avalanche Warning
Posted Monday January 7th, 2009 at 0900.

This is Steve Karkanen at the West Central Montana Avalanche Center with a special avalanche warning for January 7th, 2009. This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. This avalanche warning is valid for the next 48 hours as snow levels continue to rise. The next regular avalanche advisory will be issued on Friday, January 9th.

An avalanche warning has been issued for all mountainous areas of West Central Montana including the Bitterroot Mountains from Lost Trail to Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Rain and heavy wet snow is falling onto an extremely weak snowpack. Any snow covered slope steeper than 30° that is receiving rain is now very dangerous.

Weather and Snowpack Analysis

Weak faceted snow above and below a rain crust + a dense slab of snow above the crust + light dry snow on top of the slab + another layer of wet heavy snow above the light dry snow + rain up to 6500′ = widespread and potentially large destructive avalanches. Whenever rain is a factor in the snow stability equation the result of this addition to an already volatile recipe is widespread avalanche activity on all aspects and at all elevations below the snow line.

SNOTEL sites this morning are showing temperatures in the 30’s and 1” to 1.5” of snow water equivalent has fallen the past few hours. Conditions are ripe for avalanches

Current Avalanche Danger

In areas where rain is occurring or expected, the avalanche danger is HIGH. Natural and human triggered avalanches are likely. Travel in avalanche terrain is not recommended without extensive avalanche assessment skills. Avoid being on or under any slope steeper than 30°

The avalanche danger is CONSIDERABLE at the higher elevations where heavy wet snow is falling onto a layer of cold, low moisture content snow that was deposited last Friday and Saturday. This inverted or upside down snow is very sensitive so slopes rated as considerable will slide into the high avalanche danger category as soon as it begins raining or while receiving a heavy load of new snow. Rain is expected to reach as high as 6500′ to 7000′ by Thursday.

Recently wind loaded or unanchored open slopes are dangerous. Natural avalanches are possible, human triggered avalanches probable. There are unstable slabs on many slopes just waiting for the right trigger to rip them out. Considerable avalanche danger means there are dangerous conditions out there. BE CAREFUL!

Weather Forecast and Avalanche Outlook

From the Missoula NOAA National Weather Service Forecast Office:

NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER MOUNTAINS-BITTERROOT/SAPPHIRE MOUNTAINS-
746 PM MST TUE JAN 6 2009 /646 PM PST TUE JAN 6 2009

A WINTER STORM WARNING ABOVE 4500 FEET REMAINS IN EFFECT UNTIL 11 AM MST /10 AM PST/ WEDNESDAY. MODERATE TO HEAVY SNOWFALL IS EXPECTED OVER THE HIGHER TERRAIN THROUGH WEDNESDAY. TOTAL SNOWFALL ACCUMULATIONS OF 6 TO 10 INCHES
ARE EXPECTED…WITH LOCALLY 15 INCHES POSSIBLE. STRONG WINDS WILL RESULT IN BLOWING SNOW AND REDUCE VISIBILITY…ESPECIALLY OVER LOLO AND LOST TRAIL PASSES. SNOW LEVELS WILL RISE TO BETWEEN 5000 AND 5500 FEET BY LATE WEDNESDAY WITH SNOW CHANGING OVER TO RAIN IN THE VALLEYS. A BRIEF PERIOD OF FREEZING RAIN IS ALSO POSSIBLE.

Expect avalanche danger to remain similar or worsen until temperatures begin to drop. Slab avalanches involving the newest snow may step down to more deeply buried weaknesses once they start moving.

21 people have died in avalanches this year in the US and Canada, most of them in the past 2 weeks. Avoid travel on or under slopes steeper than 30°, never expose more than 1 person at a time to an avalanche path, carry rescue equipment and know how to use it.

SPECIAL NOTE: Many mountain ranges in Montana and Northern Idaho are not covered by avalanche advisories. Many of these areas are as popular and visited as often as the mountain ranges covered by the Avalanche Centers in this region. Backcountry recreationists seeking information about avalanche conditions in these areas should contact the local Forest Service District Office for more information. You can also interpret information provided by the Avalanche Centers, SNOTEL sites and the National Weather Service weather forecasts to determine what the snowpack conditions are like in areas that are not covered by an avalanche advisory. When avalanche danger conditions are dangerous from one avalanche advisory area to the next, chances are pretty good that mountain ranges that lie between avalanche centers have very similar conditions, particularly those ranges adjacent to covered areas. If uncertain, do call!

SPECIAL NOTE #2: Foothills areas in Western Montana are beginning to accumulate respectable snow depths. While these areas are outside of our avalanche advisory area, these areas have terrain steep enough and avalanches have happened under the right conditions. In January of 1993, a young man died in an avalanche on Mt. Jumbo within sight of East Missoula. It’s worth paying attention to during unusual winter conditions and we have unusual conditions this year.

We’ve received many excellent observations from many different locations the past few days. Your weather and snow observations are very important to us as they help us portray more accurate overall avalanche conditions in our area. Our resources are limited so information about avalanche activity or weather conditions you see may save a life. If you have any information you’d like to share or have questions about anything related to snow safety, please contact us at [email protected] .

The next avalanche advisory will be posted Friday January 9th, 2009