The Glacier Country Avalanche Center has issued a high backcountry avalanche advisory warning for northwest Montana on those steep, open slopes that have received significant amounts of either precipitated or wind deposited snow over the last three days.
The danger rating expires at midnight Friday, March 6, but the outlook is for the avalanche danger to remain near the current elevated level through the weekend as another strong weather system is forecasted to approach our region Saturday night.
Here’s the full release from the avalanche center:
WEATHER ANALYSIS:
On Thursday over NW Montana a front of cold Canadian air collided with a moist Pacific flow producing locally heavy snowfall and gusty winds and rapidly cooling temperatures. Especially impacted by new snowfall was the N’ern three quarters of the region. Over the three days of Tuesday thru Thursday many mtn locations in our northern tier along the Canadian border received 10-16 inches of new snowfall. This precipitation was initially accompanied Thursday by strong W-SW winds. By mid-day Thurs. these winds began a 180 degree reversal, blowing then from the E-NE. Thursday saw air temperatures begin the day generally in the upper 20’s F. By noon with the advancement of the Canadian air, temps began to plunge, finishing the day near zero over much of the region. Only the southern fringe of the region remained insulated as the cold air advancement slowed.SNOWPACK ANALYSIS:
Our backcountry observations Thursday were in the Madge Creek Basin on the westslope of the East Cabinet Range south of Troy on the Kootenai and in the Big Creek – Lakolaho Ridge area in the S’ern Whitefish Range north of the town of Whitefish. We received reports Tuesday from the Lakolaho drainage again in the Whitefish Range north of Whitefish and on Wednesday from the S Dickey Cr drainage up the Middle Fork near Essex.In our backcountry tours and snowpit investigations Thursday and the reports received Tuesday and Wednesday, we saw a snowpack that even prior to Thursday’s storm was harboring a fair bit of buried instability. Weaknesses were typically associated with buried surface hoar and graupel layers and poor bonding relating to melt-freeze ice sheets, layers, and crusts. Add to these conditions a significant amount of new cold snowfall and strong gusty winds on Thursday and we’ve cranked up the hazard index relating to soft and wind slab avalanching.
AVALANCHE – INSTABILITY DESCRIPTION:
We’re currently rating the avalanche danger across the region as HIGH on all steep, open slopes that have recently received significant amounts of precipitated or wind deposited snow. Unstable soft and wind slab layers are likely on a variety of aspects and slope angles. Both natural and human triggered avalanches are likely. Travel in avalanche terrain is not recommended. Safest travel is on windward ridges or on lower angle slopes without steeper terrain above. Dangerous avalanche conditions exist currently. Extensive avalanche skill, experience, and local knowledge are essential.WEATHER FORECAST & AVALANCHE OUTLOOK:
The weather forecast is for a ridge of high pressure to move rapidly over NW Montana late Friday and early Saturday. During that period we expect to see diminishing snowfall and the beginning of a shift in winds from the gusty E-NE. Friday night’s temps should remain cold in the single digits and low teens. Clouds with light snow are forecasted to increase over the region during the day Saturday as the next weather system approaches from the NW. Saturday night and Sunday should see another significant shot of snowfall, moderately cold temperatures, and 10-20 MPH W-SW winds. These conditions should maintain the avalanche danger at its current elevated level into next week.Backcountry travelers will need to be alert Friday and this weekend for signs of snow instability. The formula of cold temperatures and significant new snowfall produces enticing skiing, boarding, and snowmobiling. Mixed however with wind and a preexisting condition of isolated pockets of buried instability, the recipe can be a rude awakening to those navigating solely on joy-pilot.
Our next regular update of this advisory message will be Tuesday, March 10th.
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 message is available via telephone at 257-8402 or on the internet at www.glacieravalanche.org