Posted 8:20 a.m., Saturday, March 12, 2011
Tuckerman and Huntington Ravine have LOW avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.
Another wet storm has come and gone leaving us with increasingly stable snow conditions in the existing snow pack. Over the past two days, Hermit Lake received 1.9” (47.1mm) of water equivalent in the form of snow, mixed precipitation and rain. There was about 6” (15 cm) of new snow that fell in avalanche terrain on Thursday accompanied by S and SE winds that formed new wind slabs in the Ravines, particularly on north facing aspects. This was followed by a notable period of rain that resulted in High avalanche danger yesterday. Visibility is limited this morning, but I can see a fresh pile of wet avalanche debris in Hillman’s Highway that came from Dodge’s Drop and I expect we will see more piles of debris when the clouds lift. Precipitation tapered off late yesterday and temperatures in the start zones are now below freezing and will continue to fall during the day. This change in weather has allowed water percolation in the snow pack to slow down, reducing our concerns of natural avalanche activity. This will continue through the day resulting in Low avalanche danger in the current snowpack. As the surface crust thickens through the day it will form a nice icy bed surface that will provide a challenge for any new snow to bond to. Snow showers are in the forecast today with and inch (2.5 cm) or less of accumulation expected. Winds are forecasted to be out of the west and increasing to 45 to 60 mph (72 to 97 kph). These winds will be able to transport any new snow that does fall into the Ravines and may result in isolated areas of unstable snow later in the day. If you plan on traveling in avalanche terrain pay close attention to how much snow actually falls. Seemingly small amounts of snow accumulation can result in impressive amounts of wind slab development. If we exceed the forecasted totals by even an inch you can expect more substantial issues to develop related to new snow instability.
Additional concerns today are very similar to the ones we discussed earlier in the week after our last rain event followed by cold temperatures. Ice dams may form as temperatures dip into the teens and freeze water channels in the gullies. This can result in a build up of hydraulic pressure that can cause problems for ice climbers. Those of you planning off trail travel will quickly realize that you need snow shoes or skis to get anywhere as the snow is completely unsupportive, causing you to sink up to your waist pretty easily. And finally, as the surface continues to freeze I expect some pretty slick conditions to develop in steep terrain making crampons, and ice ax and solid mountaineering skills important to get around safely.
In addition to today, snow showers are forecasted in the mountains tonight and tomorrow. These may have a bit more vigor than those forecasted for today so there may be more significant snow stability issues developing for tomorrow. We will monitor this and keep you updated in tomorrow’s advisory.
- 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.
Brian Johnston, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856