Kootenai National Forest Avalanche Advisory – 3/14/2014

THIS ADVISORY HAS EXPIRED

The avalanche information for the Kootenai National Forest is provided by Kootenai National Forest personnel. The Flathead Avalanche Center hosts this information on its website for the Kootenai National Forest.

Issued: March 14, 2014 at 7:00 a.m. by Jon Jeresek
Expires: 11:59 p.m. of issue date

This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory for the Kootenai National Forest area will be Tuesday, March 18, 2014 by Jon Jeresek.


MOUNTAIN WEATHER 

WeatherGraphic

Since the Tuesday morning (March 11th) advisory, heavy amounts of snow (SWE 1.1”- 2.0”) have fallen in the East and West Cabinet Ranges at Kootenai snotel sites (Bear Mtn, Poorman Cr).  In the Purcell Range light amounts of snow (SWE 0.2”) have fallen.  Winds Tuesday through Thursday were from the southwest at variable speeds.  Temperatures at all sites have followed daily melt (upper 30s F) freeze (upper 20s F) cycles.  There is little soft snow available for wind transport at all sites in our Ranges due temperature impacts.

FORECAST:  Partly cloudy skies Friday through Sunday.  All daytime temperatures are forecasted to be above freezing in the upper 30s/low 40s, with night time temperatures in the mid to upper 20s.  Winds will be out of the southwest at 6 – 18 mph with LOW probability of snow transport Friday through Sunday due to temperature impacts to snow surfaces.  Chance of snow is 70-100% Friday with accumulations of 4” -6” forecasted


 RECENT OBSERVATIONS

RecentObservationsGraphic

We traveled to China Basin in the Purcells located 12 air miles northwest of Libby on March 13th.  90” to 95” of snow was encountered on east aspects at 6,000’ elevation.  4” of temperature modified new snow sits atop a 5” knife hard rain crust from the last rain on snow events.  Below this rain crust there only hard slab layers (1 finger/pencil hardness). The upper 10” of the snowpack releases easily and cleanly with 5 wrist taps using the compression stress test.  Several prolonged cold nights have help solidify the snowpack.  The mid pack hard slabs release cleanly with moderate to hard force.  Below these snow layers is the old snow melt-freeze crust.  The base of the snowpack shows depth hoar development as a result of the severe temperature gradients during the first week of February.  Currently, there are no significant temperature gradients in the snowpack to drive change processes. 

 

Debris field from other China Basin avalanche. Vertical fall 250’. 3/13/2014.

Debris field from other China Basin avalanche. Vertical fall 250’. 3/13/2014.


Wind deposit crown fracture (12’ at deepest) associated with avy incident from backside of China Basin. 3/13/2014.

Wind deposit crown fracture (12’ at deepest) associated with avy incident from backside of China Basin. 3/13/2014.


Wind deposit crown fracture (7’ at deepest) associated with another avalanche from front side of China Basin. 3/13/2014.

Wind deposit crown fracture (7’ at deepest) associated with another avalanche from front side of China Basin. 3/13/2014.


Debris field from China Basin wind slab. Vertical fall 700’. 3/13/2014.

Debris field from China Basin wind slab. Vertical fall 700’. 3/13/2014.

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

  SNOWPACK DISCUSSION

Avalanche Problem #1

Persistent Slab We have cohesive layers of hard snow positioned in the upper part of our snowpack.  When the bond to an underlying persistent weak layer breaks, these hard slabs release.  Our weak layers are associated with buried surface hoar and near surface facets.  Persistent weak layers can produce avalanches over long periods of time, making them dangerous and tricky to forecast.

 


 

 Avalanche Problem #2 

Wind SlabWinds in the Kootenai region typically transport soft snow from west/southwest aspects to deposit it on east/northeast aspects.  Subtle terrain variations modify this pattern.  Wind slabs are often smooth and rounded, and may sound hollow when traveled on.  These locations should be identified and avoided.

 

 


 

Avalanche Problem #3

WetAval

There will be increased potential for loose wet avalanches within recent unconsolidated snow as well as the potential for wet slab avalanches. Also, keep in mind that recently formed cornices may become more sensitive with warmer temperatures, continue to give them a wide safety margin when traveling above them and avoid travel below. Pay attention to the clues that warming temperatures are making the snowpack unstable like snow surface becoming wet, skis or boots penetrate deeper into the snow, or pin wheels start to roll.

 

TREND:  No significant storm loading is the forecasted Friday morning through Sunday.  We expect light wind transport (SW 6 -18 mph) of snow from Friday’s storm (4 -6”).  Temperatures are forecasted to be above freezing daytime in the upper 30s, and night time in the upper 20s through Sunday.  


  BOTTOM LINE

The avalanche hazard in the West Cabinets, East Cabinets and Purcell Range is CONSIDERABLE.  This means that dangerous avalanche conditions exist on many terrain features, especially during the height of day time heating.  Natural avalanches are possible, and human triggered avalanches are likely.  Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

SPECIAL NOTE:  Conditions change as day time heating progresses.  Be alert to this change especially on sun exposed slopes. 


 DISCLAIMER

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.