ALPTRUTH Avalanches in the area in the last 48 hours Loading by snow, wind or rain in the last 48 hours Paths, Avalanche paths Terrain Traps Rating, considerable or higher on the current avalanche bulletin Unstable snow: Collapsing or cracking Thaw instability, recent warming of the snow surface 92% of all accidents happen when 3 or more of these things are present.

A A valanches Signs of recent slides –Natural slides within the last 48 hrs –Teton Pass is closed –Debris on the roads –In or on the BT reportwww.jhsnowobs.org ALPTRUTH

Photo Peter Thurston

Photo Evan Howe

L oading Snow or rain in the last 48 hours An inch an hour for 6 or more hours, making 8” total or more Amplified by terrain features Amplified by high winds ALPTRUTH

Loading: amplified by wind From The Avalanche Handbook, McClung and Schaerer

T. Leonard Photo LoadingwindwardLeeward SafeScary!

P aths : Avalanche Paths Large and small Recognizable by a novice Funnels and fans What are the clues? ALPTRUTH

Path anatomy

Trim line, flag trees

Terrain Traps Often near creekbeds, roadcuts Often not as obvoius Consequences of being caught are amplified “nowhere to run” ALPTRUTH

Terrain Traps : Is there an escape route?

Photo Don Sharaf

Photo Brad Sawtell

Rating: what does the avalanche report say? Caution if it is Considerable, High, or Extreme ALPTRUTH

Rating ALPTRUTH

Unstable Snow Collapsing or Whumphing Shooting cracks Heavy over weak ALPTRUTH

Shooting Cracks

Photo Don Sharaf

What sound does this make when weighted?

Th Th aw Instability Rapid temperature rise: The FIRST time the temp rises degrees F in 12 hours or less after a long cold spell ALPTRUTH

Effects of Temperature on a Slab Cold temps = frozen and hard slab  Rapid warming and skier triggering  General warm temps and settlement  Wet snow and the Melt-freeze regime

Thaw Instability: rapid warming

AVALANCHE TRIANGLE WEATHER TERRAIN SNOWPACK

Red Light Factors Weather: –Recent strong winds –Recent heavy snow or rain –Sudden warming ( +12 to 15F over 12 hrs)

Red Light Factors Snowpack: –Shooting cracks, “whumphing”, recent avalanches –“heavy over weak” layering, especially with a persistent weak layer under a heavy well- bonded slab –Low scores or Q1 shears in tests

Red Light Factors Terrain: –Slopes steeper than 30, or in the runout of those slopes –Avalanche paths marked by scarred, missing, or sparse trees –Terrain traps such as gullies, cliffs, trees, crevasses, lakes –Recently wind loaded slopes –Localized areas of convexity, especially with thin snowpack and rocks underneath

Red Yellow Green Light Red Yellow Green Light Decision Making Red Light Terrain degrees -Leeward -Loaded Snowpack -Natural Avalanches -Collapsing -Shooting Cracks -Heavy over Light -Easy test scores -Q1 Shears Weather -1” an hour for 6 + hours -<12” in hours -Wind -Rapid Warming Don’t forget the Human Factor - Risk Tolerance -Experience -Group Size -Powder -Male

ALPTRUTH Avalanches in the area in the last 48 hours Loading by snow, wind or rain in the last 48 hours Paths, Avalanche paths Terrain Traps Rating, considerable or higher on the current avalanche bulletin Unstable snow: Collapsing or cracking Thaw instability, recent warming of the snow surface 92% of all accidents happen when 3 or more of these things are present.