Backcountry Snomo Report

Red Flags:
Rapid temperature rise

Updated:
Sunday, Mar 12, 2017 1:35 PM
Observer(s):
Mike Maurer
Position:
Pro Ob
Location:
Three Sisters Area (44.052438, -121.667919)
Ob Date/Time:
Sun, Mar 12, 2017 - 12:52 PM
Report Type:
Snow Conditions
Mode of Travel:
Snowmobile

Written Report:
With last weeks significant snow then rain in mind plus the recent Tumalo avalanche report from Aaron, I took my sled into the backcountry at first light this morning. I was interested in checking some of the popular play areas for cornice or slab releases, and also wanted to check the condition of the upper snowpack on both a loaded (north) and solar (south) aspect.

When I reached the Moon Mtn area I noted previous cornice releases (pic 1). Some of the high marks from yesterday had filled in with light snow overnight so its possible these releases were from yesterday. One release ran roughly 3/4 down the slope. Cornices remain notable at the summit. In the same area, I checked the upper snowpack on a south face at Checkpoint 1 before any sun had impacted the slope. Details are below. Bottom line is that 3 distinct crusts were present within the top 33cm of snow. All crusts were hard layers (P), with softer layers between them (1F). As the sun warms up these south facing slopes the softer layers could become weak enough to release the harder layers above them..

I traveled down trail 8 to the small pay area just downhill from the 7/8 junction and noted cornice releases just above recent sled tracks (pic 2). Approaching the lower section of Big Meadow just before it turns toward Todd Lake there is an popular off trail route on the south side. A steep east facing slope denotes the entrance to this area. Today the slope showed clear evidence of warming, with pinwheel and small releases on the face (pic 3). I traveled a bit further toward a north facing slope in the area and checked the upper snowpack conditions. Details are below. Bottom line here was that I found fewer crust layers than the south aspect higher up in the terrain, and the layers were generally well bonded. The top 25 cm of snow was a hard layer (P) with 10 CM of softer snow below it (1F), and then a 2 CM crust was found below the softer snow. small column tests showed hard results. Of note, when I dropped the shovel tilt column onto the snow, the uppermost layer split cleanly from the column (pic 4).

Overall I would continue to watch for weakening, sun effected snow and cornices that could release from warming and softening. I also noted a widespread layer of facets across the terrain today. Warm temps could melt away a good portion of them, but some facets could linger at higher, cooler elevations and in shady gullies, which may then be buried during the next snow event.

Details.
Checkpoint 1 Pit;
Aspect: South
Elevation: 6900'
Sky: Clr, Air temp: -3°C
Slope angle:30°
Surf form: PP and DF 1-2 mm
Results; STN, CTN
multiple ice layers within top 33 cm

Big Meadow Pit:
Aspect: North
Elevation: 6350'
Sky: Clr, Air temp: -4°C
Slope angle:40°
Surf form: DF 1-2 mm
Results: STN
CTH(25) ↓46 CM, under 2 CM crust, BRK



Weather & Snowpack
Temperature: -3°C Sky: Clear skies Wind: West @ 1-16 mph
New Snow: 2 cm Snow Depth: 300 cm Elevation: 6900 ft Aspect/Slope: South / 30°


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