February 22 Avalanche Advisory

February 22 Avalanche Advisory
Posted: February 22, 2008 at 0700
Weekend Avalanche Advisory

Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s weekend avalanche advisory for February 22-24, 2008. The avalanche danger rating expires at midnight February 22. This report is based on field observations and data collected on Thursday and describes conditions seen at that time. This advisory is the sole responsibility of the Forest Service and does not apply to operating ski areas. This weekend’s advisory is dedicated in memory of Ben Richards of Missoula, who died in an avalanche near Big Sky in March of 2007.

Weather and Snowpack Analysis
The snow stopped falling in West Central Montana by Sunday Feb. 17. Snotel sites in West Central Montana are recording significant settling, anywhere from 6 to 10 inches. This kind of settlement in the snowpack generally indicates stability. Weather telemetry also recorded temperatures well above freezing at higher elevations during the day. Two things to think about are rapid warming during the day and the production of surface hoar during the clear nights. The snow may become unstable around rock ridges or outcrops during periods of rapid warming, particularly on East aspects during the morning and West and South aspects in the afternoon. Surface hoar is being noted in the Bitterroots. This surface hoar may produce an unstable layer if we get snow on top of it. This will be something to look for on North and Northeast slopes. The sun will have destroyed most of the surface hoar on other aspects. All observers are reporting generally stable conditions but the snow in the Rattlesnakes and the Lolo Pass area have some weakness in the upper pack. The Rattlesnake Mountains had a fair amount of wind the last two weeks that was not recorded in other areas. The wind caused layers about 35 cm into the snowpack in the Rattlesnakes that warrant attention for the next few days. A layer similar to the Rattlesnake layer is also present in the snowpack around the Lolo Pass area.

Today’s Avalanche Danger

Above 6000′ in all advisory area locations, the avalanche danger is MODERATE on all slopes 35 degrees and steeper, particularly in the heat of the afternoon. Natural avalanches are unlikely and human triggered avalanches are possible. Use caution in steeper terrain. Below 6000′ the avalanche danger is LOW. Normal caution is advised. Even during periods of LOW hazard isolated areas of instability may exist.

Weather Forecast and Avalanche Outlook:
A ridge of high pressure will continue into Friday evening. A weak system will move through the region Friday night into Saturday. The higher terrain may get some accumulating snow. Snow amounts are not expected to be over 2 inches and winds are predicted to be light. Another system is expected Sunday with a possibility of more snow and winds to 10 mph. Avalanche hazard may increase during the warmest periods of the day and the surface hoar noted in the Bitterroots may get buried by the snow predicted for Saturday and Sunday.

If you want to send us an observation or report an avalanche, go to missoulaavalanche.org and click on “submit an observation”.

Many thanks to the University of Montana, Montana Fish, Wildlife & Parks and the Missoula Office of the National Weather Service for their support of this website.

Steve Karkanen will post the next avalanche advisory on February 29, 2008.