Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger today. The Lobster Claw, Right Gully, Sluice, Lip, and Center Bowl have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The Chute, Left Gully, Lower Snowfields and Hillman’s Highway have Moderate avalanche danger. 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 has CONSIDERABLE and MODERATE avalanche danger. North Gully, Damnation, Yale, and Central Gully have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Pinnacle, Odell, South, and the Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
Flat light and reduced visibility due to fog and snow showers will make assessing avalanche terrain challenging today. Our snowpack right now is complex and demands careful evaluation due to continued windloading in the upper start zones of many gullies. Our danger ratings may increase in many forecast areas today as winds slowly increase and shift directions, transporting and depositing snow in areas with a south through east aspect. Existing windslabs from previous days still exist as well, so be on the lookout for these slabs which are adhering poorly to the various suncrust layers beneath. A small wind slab avalanche on Friday in Lobster Claw stepped down through the crust which allowed the avalanche to grow to a dangerous size as deeper snow was added to the slide. The avalanche conditions now are paydirt for avalanche practitioners, guides, and educators due to the length of time since a significant thaw or rain event has “reset” our snowpack to a uniform and stable condition.
Yesterday the 1.5” (4 cm) of new snow fell mainly on N winds averaging around 25 mph (40 kph). This wind speed was just fast enough to move snow into high start zones without distributing it widely further down the gullies. Slopes look smooth right now because the light wind lacked sufficient power to hammer and sculpt the snow crystals into our more commonplace strong windboard and sastrugi. Assessing these drifts from below will put you in the crosshairs of natural avalanches when and if windloading happens or if someone triggers something above you. Where the drifts and windslabs exist on steeper slopes, they will likely be soft enough to propagate a crack for a significant distance. While the total snowfall and loading amounts aren’t great, remember that the bed surfaces are slick and enough snow is available to push you down a slope and bury you, especially if the weight of the moving slab steps down into deeper layers. Forecasted snow today totaling a trace to 2” (5 cm) on winds shifting from the NE to NW and increasing to 25-40 mph (40-65 kph) will create instabilities that lead us to believe natural avalanches will be possible in Lobster Claw over to the Center Bowl in Tuckerman and North Gully over to Central Gully in Huntington. Don’t be fooled into thinking that the rocks and bushes in the tops of these gullies will serve as anchors. The snow layers in these locations are thin and weak enough that thin spots, such as protruding rocks and bushes may serve as trigger points in the windslab.
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 8:25 a.m., March 3, 2013. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forests
(603) 466-2713 TTY (603) 466-2856