Avalanche Forecast for Friday, February 8, 2019
This information was published 02/08/2019 at 7:04 AM.
The Bottom Line
Wet avalanches will remain a concern until the snowpack is refrozen. Currently, temperatures are around 10F warmer at Ravine elevations so meltwater may continue to flow in the snowpack until mid-day. This free water in a mostly dense snowpack leads us to a LOW avalanche danger rating today. Soaking wet snow, particularly where it is sitting on steep slabs of rock, ice or ice crust could be trouble spots. Avalanche danger will diminish as cold temperatures and high winds arrive in the afternoon. Travel will be challenging through the day as soaked and rotten snow give way underfoot, even on apparently packed trails. As the snowpack refreezes, crampons, an ice ax and careful climbing will be needed to avoid a long sliding fall in steep terrain.
The melting continues at all elevations but only through this morning. Freezing rain and rain fell overnight and should continue through the day, as shower activity, until a changeover to snow in the afternoon. Currently, an inversion is keeping things colder in the valleys and the summits with temps in the 40’s F at mid-elevations. The temperature will tumble below the freezing point, by noon at Ravine levels, and continue to fall past 10F by dark, ultimately reaching 15 below zero by dawn tomorrow. Meanwhile, southwest flow will shift west into the 60-80 mph range by mid-day, then northwest at speeds close to the century mark in the late afternoon. Upslope snow showers could deliver a couple inches of snow later in the day and overnight. As always, there is no shelter on the summit of Mt. Washington in the winter.
Primary Avalanche Problem – Wet Slab
Wet slab avalanches will remain a concern until the snowpack is drained of rain and meltwater and refrozen. The snowpack will lock up today as temperatures fall but the timing of this will vary by elevation. Avalanche problems will be replaced by a long sliding fall problem in the afternoon as the wet snow surface becomes icy and bulletproof on steep slopes.
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.
Following 2-3 cm of snow, sleet and a period of freezing rain on Wednesday night, the sun and thin clouds worked to heat up the snowpack at every elevation and aspect yesterday. Field observations were limited to terrain from Pinkham to Tuckerman Ravine but the trend of settlement and melting was clear. The upper snowpack was isothermal but to a variety of depths not necessarily corresponding to elevation, likely due to the variable depth and porosity of ice crusts in the snowpack. Speaking of snowpack, ours remains deep and well developed on the east side of the range with 170cm or so on the ground in Tucks. Avalanche activity and above average snowfall have developed our typical avalanche paths, as well as some less typical ones, to full extent. The ice crusts which have developed over the past month or so have been a reminder that these icy crusts become slick bed surfaces that encourage far running avalanches. We should have another one of these layers in place on the surface by Saturday morning.
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 02/08/2019 at 7:04 AM.
USDA Forest Service
White Mountain National Forest