January 4 Avalanche Advisory

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for January 4, 2010.

Current Avalanche Danger
There are pockets of CONSIDERABLE avalanche danger above 6000′ on terrain steeper than 35 degrees.
We are seeing failures in our stability tests in the top 25cm (10”) of snow and in the depth hoar toward the bottom of the snowpack. We received a well-documented report of a skier-triggered slab near Lolo Pass on 1/2/10. This avalanche was on a steep slope and was 25cm (10”) deep from the surface. We have also received reports of other skier and rider – triggered avalanches in the Bitterroot near Lolo Pass and Lost Horse Creek.
These pockets of CONSIDERABLE danger are on steep slopes void of anchors or rollovers associated with rocky outcroppings.
On other terrain above 6000′ and steep terrain void of anchors above 5000′ the avalanche danger is MODERATE.
On all remaining terrain above and below 5000′ the avalanche danger is LOW.

Weather and Snowpack Analysis
I don’t want to sound like a broken record (cd or mp3) but we have an interesting scenario in West Central Montana right now. The region received anywhere from 5 to 10 inches of new snow since New Year’s Day. Before the new snow arrived surface hoar had formed on the top of the snowpack. The surface hoar had been destroyed by sun and wind in the Rattlesnakes but not in the Bitterroots. The avalanche near Lolo Pass reported in the “current danger” was the new snow running on the surface hoar. We had the same surface failures in stability tests in the Rattlesnakes but it appeared to be a density change in the snow (the snow came in cold and finished warm). What is worrisome is in stability tests the snow is still failing on the depth hoar formed from early season.
The top layer avalanching could be a problem if it went into a terrain trap (i.e. over a cliff or into a gulley) and the top layer avalanching could step down to the weak snow in the bottom of the pack. There is some skiing or riding to be had out there but you need to pay close attention to steep terrain.
The You Tube shot explains the variability in our pit tests. But the difference in the tests has been the amount of force applied; the same layer continues to collapse cleanly.
I noted the same variability with backcountry recreationists this weekend. I talked to some cagey veteran backcountry skiers who turned around after snow observations. I saw some folks ski a conservative, anchored line one at a time and I saw some riders hucking cliffs with their buddies standing immediately below. The activity from the last observation is not advisable.

Weather Forecast and Avalanche Outlook
Pacific Moisture may collide with cold Canadian air over the region on Monday and Tuesday. As of this advisory it’s not clear how quickly the Canadian air will surge into Western Montana. Moderate to heavy snowfall is predicted along the Continental Divide along with Northeast winds. Wednesday should bring drier and colder conditions.
Expect the surface instability to increase with new snow amounts. With more snow the surface slab will be thicker as well. If we get new snow, winds and the predicted colder air the avalanche hazard will not decrease.
Keep in mind that our winds generally come out of the Southwest. Northeast winds are predicted for this storm; which makes all steep slopes above 6000′ suspect.

Steve Karkanen will post the next advisory on 1/8/10.

For Beacon Park information go to http://mslaavalanche2.wpengine.com/beacon_training.php .

If you get out and see avalanche activity or want to send us quick snow observations, send us a note at [email protected] or call us at 406-530-9766 (530-9SNO) .