Avalanche Forecast for Wednesday, February 6, 2019
This information was published 02/06/2019 at 7:07 AM.
The Bottom Line
Warm temperatures and sunshine will again bring the potential for wet slab avalanches today. If you find yourself sinking into the snow to your boot-tops or more, you have found the avalanche problem. Yesterday’s warm up did not reach beyond 20-30 cm so plenty of dry snow beneath is waiting to get wet and contribute to the possibility of a human-triggered avalanche today. Evaluate snow and terrain carefully for signs of this heating and find another aspect or lower angle slope to ski on. MODERATE avalanche danger exists at all elevations today due to the potential of stubborn but large slabs in isolated areas. Wet slabs and wet loose avalanches will be more reactive in steep terrain where heating is most intense. Be alert for cloud cover and cooling temperatures that could refreeze the snowpack this afternoon and create the potential for a long sliding fall.
The temperature on the summit reached 34F for the second day in a row yesterday with mixed sun and clouds and temperatures at 3800’ reaching 42F. Temperatures cooled to 12F on the summit late last night before climbing to 25F again at 3am, with warmer temps at ravine elevations. Another warm day is on tap after last night’s brief cool down. Expect temperatures near 30F on the summit with temps likely to be well into the 40’s in the ravines. Relatively light wind on the summit, 20-35 mph, will allow maximum heating mid-day prior to clouds rolling in later in the afternoon. Freezing conditions may return before dark.
Primary Avalanche Problem – Wet Slab
Wet slab avalanches are likely to be stubborn today. Softer snow or thinner slabs will make it easier for a crack to propagate. An icy bed surface beneath the most recent snowfall and wind loaded slopes make today’s avalanche problem worse, particularly in areas of previously wind drifted snow. Wet slabs could be large enough to bury a person.
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.
Warm air temperatures, a bit of rain and some sunshine started the upper snowpack on the road to becoming isothermal yesterday. The process only made part of the way down into the snowpack where wet snow was above dry snow to variable depths at observed locations. You may have noticed fractures and slides from metal roofs, snow falling off of evergreen tree branches. If you were in avalanche terrain, you would have seen wet snow that could easily form a snowball in one hand, but only in the top few inches unless you dug in a an area where a drainage channel was established. As long as dry snow remains sandwiched between the warming, wetting and weakening upper snowpack and the thick and durable ice crust formed on January 25th, avalanche danger will remain elevated.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 02/06/2019 at 7:07 AM.
USDA Forest Service
White Mountain National Forest