February 27, 2012 Avalanche Advisory

At all advisory area locations above 6000 feet, the avalanche danger is CONSIDERABLE on all wind loaded terrain steeper than 35 degrees.

The avalanche danger is MODERATE on all other terrain.

This is Steve Karkanen with the West Central Montana Montana Avalanche Center’s avalanche advisory for February 27, 2012.

Snow and Weather Analysis

Wind and more snow since Friday have made conditions a bit tricky for safe skiing.  While the skiing is as good as it gets with 20 cm of 7% moisture content snow on the surface, Saturdays wind crafted touchy wind slabs in many areas.  The ski patrol at Montana Snowbowl was able to release a few class 1 slabs in areas that were cross loaded on west facing slopes during their explosives testing Sunday morning.

Skiers in the Bitterroot mountains mentioned high wind Saturday and avoided wind loaded terrain and skied the trees.  A party in the Glen Lake area noted the inverted nature of the Snowpack Saturday and were getting moderate range stability test scores. They also reported a more alarming Extended Column Test (ECT) score with complete propagation 65 cm deep on a layer of buried surface hoar.  They wisely stuck to the lower angle terrain.

In our stability testing in the Rattlesnake Tim and I found the easiest failures were at the level of a density change just below the stiff wind slab that formed during last Wednesday’s storm.  We did not observe any collapse or fracture while traveling however we were getting the slab to propagate across the column with the ECT.  (ECTP11 Q1 40cm down).  The buried surface hoar layer is gaining strength and did not fail as easily as we saw last Thursday but it is very possible that a failure of the slab could step down and involve a much bigger slab.

Conditions are improving but require a great deal of respect for a few more days especially any steep wind loaded slope below the ridges.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting a ridge of high pressure to be over the area Monday and Tuesday with the next chance for snow  sometime Wednesday as a broad area of low pressure moves into the Northwest.

Expect avalanche conditions to slowly improve over the next couple of days and be wary of wind slabs at the higher terrain.

Tim will issue the next advisory on Friday, March 2.