March 16 Avalanche Advisory
Posted Monday March 16th, 2009 at 0630.
Good morning! This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for March 16th, 2009. This will be the last Monday avalanche advisory for this season. 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 you can use the information we provide below to help you make more informed decisions regarding travel in avalanche terrain for the next few days. Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to near Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Avalanche information about the St. Regis Basin can be found on the Idaho Panhandle National Forest Avalanche Center website.
Weather and Snowpack Analysis
Mountain temperatures climbed into the forties under bluebird skies Friday and Saturday which left a zipper crust on nearly all but the most heavily shaded slopes. A strong cold front began moving through West Central Montana Sunday bringing gusty winds and moderate to heavy snowfall in some areas above 5000 feet. Not enough snow had been deposited with this system for it to be much of a problem Sunday but we did note that the thin sun crust fails easily with light force. This Bitterroot Mountains are currently receiving the heaviest amount of snow and we did receive a report that the newest snow is moving easily on very steep terrain above 8000 feet. This morning most SNOTEL sites have received several inches of new snow the past 12 hours. Wind speeds on Point Six have been in the 20-30 mph range.
The primary avalanche concern for the next couple of days will be wind slabs that form during this frontal passage. In addition to wind slabs, heavy new snow on the thin sun crust that formed Friday and Saturday will also be a potential safety consideration in areas that receive a foot or more of snow in the next few hours.
Current Avalanche Danger
At all advisory area locations above 6000 feet on wind loaded terrain steeper than 35 degrees, the avalanche danger is MODERATE. Natural avalanches are unlikely but human triggered avalanches are possible. On all other slopes above and below 6000 feet, the avalanche danger is LOW where natural avalanches are very unlikely and human triggered avalanches are unlikely. You can almost always find isolated pockets where there are dangerous avalanche conditions on some terrain features.
Weather Forecast and Avalanche Outlook
A moist Pacific storm is currently moving through the Northern Rockies. Moderate to heavy snow will occur along with strong gusty winds ahead of, with and behind the cold front. Winter weather advisories have been issued for the mountains of Western Montana. Weather models are predicting a more zonal upper level flow for the next few days with Pacific moisture feeding into this flow for continued mountain snow showers. Significant moisture is not expected during this time frame.
Expect avalanche danger to increase during periods of heavy snowfall and high winds. We’re beginning to see more spring like conditions in the mountains which means we can go from 4 degrees to 40 in just a few hours or go from skiing and riding melt-freeze corn snow to knee deep powder overnight. Just remember that snow does not like rapid change of any sort so as conditions change we also need to adjust our assessment of just how strong a particular slope is.
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 avalanche danger scale is undergoing revision and your input is desired! This is the last week the survey will be available so take a few minutes to weigh in. It only takes about 10 minutes, is kind of fun and you may even win a prize!
The next avalanche advisory will be issued Friday, March 20th, 2009. We will no longer (for this season) issue regular avalanche advisories on Mondays. We will post information if needed based on weather and snowpack conditions.
