Posted 8:15a.m., Wednesday, March 16, 2011
Tuckerman Ravine: Hillman’s Highway, the Lower Snowfields, Left Gully, Chute, Center Bowl, Lip and Sluice have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Right Gully and Lobster Claw have Moderate avalanche danger. In these areas natural avalanches are unlikely and human-triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human-triggered avalanches are unlikely.
Huntington Ravine: The Escape Hatch, South, O’Dell, Pinnacle, Central and Yale Gullies have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Damnation and North Gullies have Moderate avalanche danger. In these areas natural avalanches are unlikely and human-triggered avalanches are possible.
As of 6a.m. snow has begun to fall in the higher terrain and the day’s weather system is ready to march on through. SW winds are currently holding steady at 35 mph and the mercury is on the rise. While most of the state will see snow that quickly changes to rain today, the summit is expecting snow to hang on longer and then change to mixed precipitation. The valleys surrounding the mountain are currently seeing their first snowflakes but they are also expecting rain before long so the big question is what will happen in the start zones of our avalanche terrain today? Summit forecasts are calling for 1-3” (3-8cm) of snow today before a change to mixed precipitation. Winds should stay out of the SW to the SSW for the majority of the day with a slide to the W late in the forecast period. Speeds will push to 50mph which should be more than enough to transport snow into the lee start zones. Even if lower portions of the forecast areas are seeing rain today the start zones and terrain above may be collecting snow that will be quickly transported via the wind.
All forecast areas started the morning with Low avalanche danger but they’ll see increasing avalanche hazard as the day progresses. With 1” of new snow, areas in the direct lee (NE to NNE) would struggle to reach the Considerable rating and the remaining areas would lag even farther behind. In a 3” snowfall scenario the forecasted ratings would be easier to reach but there is another factor that will help assure that they make it there—the afternoon’s mixed precipitation. As previously mentioned we will see a trend of decreasing stability as the day moves along with peak instability expected in the afternoon when mixed precipitation begins adding weight but no strength to the snowpack. New unconsolidated snow in steep terrain may create sloughs, some large, when this begins. New windslab will likely hold on longer but when the snow fails more area and mass will be involved. Our forecasted ratings always focus on slab avalanches but it’s important to remember that a slough or loose snow avalanche can knock you over or bury you as well.
Snow that is falling today will land on exposed rain crust in many areas. This surface is extremely slick and will make for a poorly bonded interface. It also makes for difficult travel conditions and yesterday we had one accident at the bottom of Right Gully when someone took an uncontrolled slide. Carry and use the appropriate mountaineering equipment such as an ice ax when in steep terrain. If you are not solid with your self-arrest skills you may be in for a long and unenjoyable ride.
- Safe travel in avalanche terrain requires training and experience. This advisory 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.
- Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
- This advisory expires at midnight. A new advisory will be issued tomorrow.
Justin Preisendorfer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856