February 24, 2012 Avalanche Advisory

In the southern Bitterroot mountains from Lost Trail Pass to a soft line near Lolo Pass the avalanche danger is HIGH at elevations above 6000 feet on terrain steeper than 30 degrees.

The avalanche danger is CONSIDERABLE on slopes steeper than 35 degrees above 6000 feet in the northern Bitterroot from near Lolo Pass north to Lookout Pass as well as the Rattlesnake Wilderness and southern Mission and Swan mountains near Seeley Lake.

All other terrain below 6000 feet has MODERATE avalanche danger.

Good morning skiers and riders, this is Steve Karkanen at the West Central Montana Avalanche Center with the regular Friday morning avalanche advisory for February 24, 2012.

We are allowing the general avalanche warning to expire but are posting HIGH avalanche danger for the Bitterroot Mountains above 6000 feet south of the Lolo Pass area. 

 

Weather and Snowpack Analysis

Wednesday’s storm favored the southern mountains this week with the area around Lost Trail Pass and the Twin Lakes basin getting hammered. Saddle Mountain SNOTEL reported 3.2 inches of SWE since Presidents Day and Twin Lake SNOTEL reports 4.4 inches SWE.  Lost Trail Ski Area was reporting 36 inches of accumulated snow for their Thursday opening.

Ed Snook and Rich Raines were getting easy failures during stability testing and reported a 1 finger hard slab sitting on a buried surface hoar layer.  They stress that this big slab will have big consequences if triggered.  They feel the area will have HIGH avalanche danger for 2-3 more days.

Further north the mountains saw a lot less snow and a lot more wind. Winds were still moving snow Thursday and nearly everywhere you travel you found fresh wind slabs.  Some of these are more sensitive than others. The ski patrol at Montana Snowbowl was cratering these slabs Thursday during explosives testing as opposed to the easy slab failures they were getting the day before with ski cuts.

We experienced localized whoomping, fracture propagation and alarming stability tests while touring in the Rattlesnake .  A 40 cm slab on buried surface hoar scored ECTP2 Q1 on an ENE aspect at 7000 feet. This was on a small slope that collapsed on us while we we about to dig a pit.  Similar scores in other locations kept us away from steeper open terrain.  The wind affected just about every slope so it really wasn’t very good skiing anyway. It is excellent snow for travel.

At the passes, observers at Lolo Pass noted that elevations below the rain line are set up solid and it isn’t until they gained elevation that they were seeing poor bonding of the new snow.  At Lookout, Dan Frigard reported a great deal of variability in his stability testing with the main concern being 20cm of the newest snow failing easily in his pits.  Overall avalanche danger is MODERATE here with open wind loaded terrain having the most potential for trouble.

 

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting heavy mountain snow for the Northern Rockies this weekend. Expect minimal snowfall today then increased precipitation with high winds Friday night through the weekend.  The best chance for accumulating snow is Saturday night through Sunday am.

The heavy snow in the southern Bitterroot needs a bit more time to adjust to the new load.  Keep in mind that a now deeply buried layer of surface hoar crystals is the issue and may remain with us for some time yet.  Another shot of heavy snow and high wind will again add stress to an already stressed out condition.

Stay tuned to NOAA Weather for the most current weather information and check the backcountry weather forecast that is updated every day by 1500 hrs.

We’ve been receiving many good reports about snow conditions and avalanches either witnessed or triggered by someone.  These really help us out and could help save a life.  You can use our automated form or simply email us at info@missoulaavalanche.org.

I will post the next regular advisory this Monday, February 27, 2012.