This information was published 04/14/2020 at 6:38 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Wet slab avalanches are becoming increasingly unlikely as the snowpack drains and refreezes through the day. This avalanche type is challenging to predict, so give large wind slabs in steep terrain a wide berth to increase your safety buffer. Avalanche danger is MODERATE, trending to LOW.
In addition to wet avalanches, objective hazards resulting from a large volume of rain will be found. Watch for obvious holes in the snow, undermined snow that can collapse suddenly, swollen streams, and water running behind ice flows. The Little Headwall area of Tuckerman Ravine will likely be an open waterfall today. Historically, the Lip area of Tuckerman Ravine becomes significantly undermined as a result of big rain events producing large caves of moving water and best avoided until fully drained.
When the wet snow refreezes, a long sliding fall hazard will be created requiring the use of crampons and ice axe.
Yesterday, the summit of Mt Washington received 1.4” of rain with temperatures above freezing the entire day, and Harvard Cabin snow plot received 2.4” of rain. Rain ended around midnight with temperatures dropping below freezing on the summit by 1am. The summit reached a high temperature of 41F.
Today we start the day with the summit at 14F and 27F at the Harvard Cabin (3520’). Temperatures will remain in the teens F with slowly clearing skies. West wind will decrease from 60-80 mph to 30-45 mph.
Tomorrow, cloudy skies are forecast with temperatures in the lower teens F. West wind will shift NW 35-50.
Primary Avalanche Problem – Wet Slab
Moist or wet snow may exist within the snowpack creating the possibility for a Wet Slab Avalanche until the snowpack drains entirely of free water, or refreezes. The largest slabs are found in Tuckerman Ravine and the Gulf of slides, though any wind slab found in the range today will be subject to this instability issue. Stability will greatly increase through the day, but with the uncertainty of timing associated with the fact
What is a Wet Slab Avalanche?
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
Wet Slab avalanches are difficult to predict, though tend to occur most often at the onset of rain, and stabilize soon after the rain ends. With yesterday’s rain event producing such a large volume of liquid water, it’s best to be conservative with trying to predict what’s happening under the snowpack and be cautious until obvious signs of stability present themselves. Time is on your side as stability increases through the day.
Safe travel in avalanche terrain requires training and experience. This forecast is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 04/14/2020 at 6:38 AM.
USDA Forest Service
White Mountain National Forest
Sign up to get the daily MWAC avalanche forecast in your inbox