Avalanche Forecast for Tuesday, February 5, 2019
This information was published 02/05/2019 at 7:13 AM.
The Bottom Line
Warming weather makes wet slab avalanches possible to trigger today. Avalanche danger will continue to increase through the day and only decrease when our snowpack refreezes, which may begin tonight. Loose wet sluffs, particularly if initiated by a skier or snowboarder, are also possible. If you’re travelling on soft, wet snow today in steep terrain, you’re travelling on the avalanche problem. All forecast areas have MODERATE avalanche danger.
Temperatures have been well above freezing in most of our terrain since early yesterday morning, with the summit hovering around the freezing mark. Light rain showers this morning, which may include some mixed wintry precipitation will taper off through the day. Rain totals will be less than a tenth of an inch, which is similar to yesterday’s totals. West summit wind near 60 mph will decrease tonight and tomorrow. Our middle and lower elevation terrain should return to below freezing temperatures tonight and remain so tomorrow, with a temperature inversion possibly keeping the summits a bit warmer. A trace to 1” of snow may fall this evening as temperatures fall.
Primary Avalanche Problem – Wet Slab
Wet slab avalanches are possible today with continued warming increasing likelihood through the day. This avalanche problem is generally confined to the wind slabs which formed last week, now getting wet from the rain and warm air. You’re likely to find most of these slabs on the eastern half of the compass rose and wall to wall in many gullies. Areas previously scoured to the hard January 25th crust are unlikely to produce wet slab avalanches and they will also provide more supportable and enjoyable climbing and skiing conditions. This crust is the likely bed surface for wet slabs where buried. Remember that wet slabs are difficult to predict and that stability tests results won’t be very helpful today, making lower consequence terrain a wise choice.
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.
Secondary Avalanche Problem – Wet Loose
Wet loose sluffs will be possible in the same terrain which may produce wet slab avalanches and should also be on your mind in steep lower elevation terrain where wet slabs are less likely. While rarely able to bury a person, remember that sluff and particularly heavy wet sluff in the wrong place can still sweep you off your feet and have serious consequences. The weight of sluff debris could also trigger a larger wet slab avalanche.
What is a Wet Loose Avalanche?
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
The combination of rain and warming air temperatures which has been wetting our upper snowpack will continue today. Essentially all former wind slabs are becoming wet slabs. The current upper snowpack structure of slabs over the January 25th crust as a bed surface contributes to our concern for wet slab avalanches today. As with the recent wind slabs, a person is more likely to trigger a wet slab today where the slab is thinner. That said, wet slabs are difficult to predict and may surprise you with where and when they release. Increasing depth of moisture penetrating the old wind slabs is the primary driver of instability today. Though outside of our forecast area, a large wet slab avalanche that likely released naturally was observed on Mount Mansfield yesterday.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
Massachusetts folks, we’d love to see you at an Avalanche Awareness presentation at an REI store this week. Tomorrow’s event in Boston is wait listed, but there’s plenty of space at the Framingham store’s bigger venue on Thursday evening! Check out our events page for details.
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 02/05/2019 at 7:13 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest