This advisory expires tonight at 12:00 midnight.
All forecast areas of Tuckerman Ravine have CONSIDERABLE danger. Dangerous avalanche conditions exist. Natural avalanches are possible and human-triggered avalanches are likely. Lobster Claw, the Lower Snowfields, and Little Headwall are not posted due to a lack of snow in these areas.
Huntington Ravine has Moderate and Low avalanche danger. Yale, Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. North and Damnation have Low avalanche danger. Natural and human-triggered avalanches are unlikely.
AVALANCHE PROBLEM: Wet slabs and persistent slabs are the avalanche problem today. Prolonged warming and the potential for light rain will have a destabilizing effect on the snowpack in both ravines. The biggest factor in determining where this danger can be found is how much snow is in the particular location. Areas with the least total snow cover, such as North and Damnation Gullies, will have relatively little avalanche danger. The Sluice, Lip, and parts of the Center Bowl have the greatest potential.
Also be wary of rock and ice falling from steep terrain today. Yesterday we saw a lot of small pieces of ice fall from S-facing cliffs in the Sluice and Right Gully. I expect this to be more pronounced today and spread across other aspects as well.
WEATHER: Temperatures today will likely be warmer than they have been yet this year. Early this morning, ravine elevations were already well over 40F (4C). Summit temperatures are forecast to rise into the 40s as well. Along with this, we may see about a tenth of an inch of rain. Wind speeds will be increasing as well; anyone out after dark can expect to be blown about quite a bit as gusts exceed 100mph (162kph). Showers of rain are forecast,especially later in the day, though total amounts should remain light.
SNOWPACK: There is no doubt that our snowpack is going to take a hit from this warm spell. We spent some time in the field yesterday trying to determine how the warmth and rain would affect the avalanche terrain. The short answer to the question is that the warming will destabilize the snowpack. But just how much and will it trigger avalanches naturally? That remains to be seen. I think the potential exists for naturally triggered avalanches in many areas. In Right Gully through the Chute, we believe there is a near-crust facet layer sitting underneath slab that formed after two recent snow events, March 1-2 and March 7. The crust we found in Right Gully was at least 80cm thick and hard as rock, so I doubt there are any concerns in or below this layer. This crust layer was the likely bed surface for the Lip/Center Bowl avalanche whose crown is still visible in the bowl. So the biggest hazard lies in the hangfire from here as well as the areas that have reloaded such as the Lip. The Sluice and Chute in Tuckerman, as well as Central Gully in Huntington, have the largest areas of slab where I suspect this facet layer could be found hiding underneath. Parts of Left Gully had a concerning graupel layer under a few inches of slabs; this setup might be lurking elsewhere as well. The most stable areas out there today will be where the crust is not well-buried, so that the heat can penetrate the overlying slabs and help them adhere to the very stable layers below, examples include much of Hillman’s or the northern gullies of Huntington. You can see additional information from yesterday’s field work in this post.
- 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.
- Posted 7:15a.m., March 9, 2016. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856