Crust hunt at Broken Leg North

Location Name: 
North Broken Leg Mountain
Observation date: 
Monday, March 8, 2021 - 11:00

Is this an Avalanche Observation: 
Yes
Observation made by: Public

Tabs

Quick Observation

Toured up North Broken Leg Mountain to map the crust generated by the big thaw last week and see how things are holding up.  Suffice to say the crust was everwhere and supportable making travel actually pretty easy.  Not the day to let the skis run however.  A better day to reflect on how easy it is to check your speed in nice deep powder.  

Was able to confirm the paths of the long wet loose slides on the south aspect of Crater Mountain (photo) viewed with binocculars from the valley floor on 3/3.  No other notable slides were observerd.

Temps were cool and the sun was shining.  All the mayhem occurring during the thaw was frozen in place for easy inspection but had begun to warm on SW aspects by ~12:00

So, for the crust hunt:

4100'  10cm firm crust over wet packable snow.  Total snow depth (TSD) really getting thin down at this elevation. NW aspect

4500'  7cm firm crust over moist packable snow.  62cm TSD.  A micro-dusting of new snow   NW aspect

4800'  6cm firm crust over a 6cm less firm layer and moist below that.  80cm TSD.  About the only place the crust would fracture under the skis.  A dusting of new.   NW aspect

5200'  6cm firm crust over ~10cm of firm windpacked snow (this is sort of a windy spot)   Moist below that.   ~1cm of new.  WSW aspect

5350'  4cm crust over snow that seemed a bit drier.  1cm of new.  ~100cm TSD.  WSW aspect

5670'  3cm crust linked to a couple other (windboard?) layers below (photo) over dry-moist snow.  This is also a bit of a windy spot.  SW aspect (pit dug nearby)

6000'  Thicker but less firm 8cm crust with similarly dry-moist snow below.   2cm of new.  SW aspect  Softer skiing and actually leaving tracks up here!!!

6150'  Similar 8cm surface crust layer with 2 cm of new with a VERY small fraction of surface hore visible under the scope.   SW aspect on ridgetop.

 

Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Swan Range - West Side (Flathead Valley access)
Activity: 
Skiing
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Aspect(s) of observation: 
SW
W
NW
Persistent Weak Layers: 
Not observed
New Snow in the past 24 hours: 
1.00in.
Total Snow Depth: 
117 cm
More comments about the snowpack and weather: 
Dug this pit very close to the 2/28 location to see how they compare. Interesting how different they are. Surface is warming. Bottom layer is becoming more isothermal. Most snow crystals are becoming rounded. Did not detect any fractures with a CT or ECT but was able to muscle an ugly fracture about 80cm above the ground with hard force shovel shear. Interpretation beyond these observations will have to be left to the experts.
Blowing Snow: 
None
Wind Speed: 
Calm (No air motion)
Wind Direction: 
Northwest
Air temperature: 
Below Freezing
Snow line: 
valley floor in the morning but rapidly warming
Sky Cover: 
Mostly Clear (FEW)
Highest Precipitation Rate: 
No Precipitation (NO)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Wednesday, March 3, 2021 - 15:00
Number of avalanches: 
4
Avalanche Type: 
Wet Loose
Failure Plane/Weak Layer: 
Unknown
More information or comments about the avalanche: 

Confirmation of wet loose slides viewed from a poor angle on the valley floor on 3/3 (see photo)

Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
40
Aspect: 
South
Starting Elevation: 
~6200
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R3 Medium
Avalanche Length (Vertical Run): 
1000ft.
Hide People Involved
Number of people caught: 
0
Number of partial burials: 
0
Number of full burials: 
0
Avalanche Location: