March 9 Avalanche Advisory
Good morning. This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for March 9, 2009. This information is the responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight. But, the advisory can provide valuable information for evaluating avalanche hazard for the next 48 hours.
The advisory area includes the Bitterroot Mountains from Lost Trail to Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Detailed avalanche information about the St. Regis Basin can be found on the .Idaho Panhandle National Forest Avlanche Center website.
Weather and Snowpack Analysis
We received more snow in the region since Thursday. The scenario was good for general stability. The snow associated with the storms on Thursday came in with relatively warm temperatures and temperatures have progressively gotten colder in the mountains since then. The warmer snow seems to have bonded well and the snow from Sunday was very cold, light density snow. Something that did happen this weekend is what the Weather Service refers to as banding. Banding is short periods of very intense snowfall in a local area. Specific areas picked up as much as 7 to 8 inches of snow early Sunday morning. This new snow was readily sluffing on steep aspects naturally and from human triggers. A large enough sluff can knock a person over or push them into rocks or trees. The Rattlesnakes was one of the areas hit by the banding of snow. I toured there yesterday and noted no obvious signs of instability other than the sluffing. My pit tests did reveal that that we still have crusts buried in the snowpack. Hard melt-freeze crusts on southerly aspects and deeper crusts from late January and early February on Northerly aspects can still be found. It takes a lot of force for the snow to react on these layers, but they are still with us. It is worth checking the snow with a quick snow pit before committing to a steep slope. The other thing to pay close attention to is wind loading. As I mentioned the newer snow is very cold and light and will be easily transported by the wind.
Current Avalanche Danger
On all slopes above 6000 feet and 35 degrees or steeper the avalanche danger is MODERATE. Natural avalanches are unlikely and human triggered avalanches are possible. Below 6000 feet the avalanche danger is LOW. Natural and human triggered avalanches are unlikely.
Weather Forecast and Avalanche Outlook
The chances for snow will increase today and this evening and continue into Tuesday. Drier and much colder air is expected after this. It looks like the winds may come from different directions during these changes so pay close attention to local wind loading. Remember this cold snow will move easily with the wind increasing the chance of wind slab formation.
If you have snow observations or any snow information you’d like to share please contact us at [email protected].
The next avalanche advisory will be issued on Friday, March 13, 2009.
The avalanche danger rating scale is being revised. The opinion from folks who use the advisories is important. Please take time to fill out the avalanche danger rating survey .