Mar 12, 2012 @ 6:34 am

Avalanche Advisory March 12, 2012

On slopes steeper than 35 degrees and on wind-loaded slopes there is MODERATE Avalanche Danger in the west central Montana backcountry. There is LOW Avalanche Danger on other terrain in the advisory area.

Good morning, this Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for March 12, 2012.

Weather and Snowpack Analysis

The weather was sunny and warm Friday and Saturday and numerous wet surface slides were noted throughout the area. Some had significant debris; as you can see in this picture of a wet point release that ran Friday in the Rattlesnakes on a west slope.  A bit more cloud cover yesterday cooled things down a bit and mountain temperatures are much colder this morning. The cooler temperatures helped avoid the rapid warming in the afternoon and stabilized the snowpack.

The very warm weather created a melt-freeze crust on northerly aspects and a sun crust on southerly exposures. We can expect that any new snow will be sitting on these crusts. It started snowing yesterday and the Idaho border has picked up most of the snow (3 to 4 inches of new snow this morning).  The winds started picking up yesterday afternoon also; with gusts up to 50mph on the ridge tops. Steep leeward slopes will be most susceptible to producing small slides.

The persistent surface hoar layer from early February appears to have strengthened. We took this video yesterday to show the layer and the use of the Propagation Saw Test (PST). The PST works well to test a deeper weak layer for propagation. If a weak layer, you have identified with a Compression Test, will not propagate with the Extended Column Test, the PST may get that layer to react. Here is a link to a site that shows how to perform the PST.

Weather Forecast and Avalanche Outlook

It looks like we’re headed into a series of Pacific storm systems and the temperatures will warm again.  Snow levels will generally be above 4500 feet but the possibility of snow levels rising to 7000 feet exists on Wednesday.

I would expect the avalanche danger to rise with accumulations of wet, heavy snow. Remember the melt-freeze and sun crusts this new snow will be sitting on. With any rain at elevations up to 7000 feet the snow will become very unstable. Wind-loaded slopes and cornices will be very hazardous with high temperatures, wet snow accumulation and/or rain.

If you head into the backcountry this week, as always, ski and ride safe!

Tim will issue the next scheduled advisory Friday, March 16.


This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.