Wet Slab Avalanche, 12/21-12/22 rain storm

By Ryan Matz | MWAC Forecaster

Date of Observation: December 23, 2018  9:00 AM
Location of Observation: Tuckerman Ravine Headwall area- The Lip

First visibility following rain storm, large wet slab avalanche crown and debris observed. Suspected occurrence late Friday 12/21 or early Saturday 12/22.
WS-N-R3-D2 (Wet Slab, Natural Trigger, Medium size relative to path, Large enough to bury, injure, or kill a person)
Crown height up to ~10′, width ~175′
Vertical fall ~500′
Horizontal run ~1250′
Runout angle ~22 degrees

Pertinent weather history: 3″ of rain on the summit in 36 hours, including 1.75 inches between 6:00 AM and Noon on Friday 12/21. Temperatures above freezing for 48 hours.


Snowpack observations are one part of the complex puzzle which is your decision to enter avalanche terrain. Some observations may include stability tests. It’s important to understand that the results of a stability tests are seldom conclusive anywhere, but particularly in snow climates and terrain like ours where the primary driver of instabilities is wind drifted snow. Many stability tests exist and each works best with specific avalanche problem types. Stability test results should never be used alone as an indication that a slope or conditions are safe particularly when more obvious red flags are present. Please use this page as part of your information gathering process, but don’t make decisions based on a single piece of information. A good article that summarizes some of the issues associated with snow and avalanche observations can be found here.

The Mount Washington Avalanche Center cannot verify the quality or accuracy of any observations that come from the general public.


See an avalanche or evidence of previous avalanche activity?  Near-miss? Snowpack observations?

Your observations are valuable to an accurate forecast! We welcome observations from everyone. You don’t need to be an avalanche professional to submit helpful observations, just be as detailed and accurate as you can.