Posted 8:23a.m., Sunday, January 30, 2011
Tuckerman and Huntington ravines will have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely. The only exception to this rating is the Little Headwall in Tuckerman which has Low avalanche danger. Natural and human-triggered avalanches are unlikely in this area today.
This morning’s alpenglow was like a dream. The tops of the ravines were ablaze in sunlight, barely a cloud was in the sky and the windless conditions made you forget that the mercury was still sitting below 0F at the summit. Everything continues to appear so calm and peaceful but you just wait eight hours! A passing disturbance has already started to cause the clouds to thicken and snow flurries to develop. Maybe an inch (2.5cm) of new snow will fall before a trailing cold front pushes in and things begin to get interesting. When this happens we’ll see an increase in winds as they blow out of the W at speeds up to 50mph (81kph). These weather variables by themselves are probably leaving you scratching your head and wondering how the avalanche danger ratings have climbed in all areas today. All you need to do in order to answer your own question is go kick around the Alpine Garden or Bigelow Lawn. Since Thursday the Observatory has recorded just under 4” (10cm) of snow with an overall density of 3.1%. Fluff like this isn’t very well designed for typical Mt Washington winds but the readings from the summit anemometer have been lower than normal since the low density snow began falling. It hasn’t gusted over 50mph (81kph) since Thursday morning and yesterday’s average wind speed was a mere 13mph (21kph)!!! During this period the blanket of champagne powder has lain waiting for the wind to set its travel plans in motion and today looks to be the day. Wind-transported snow should begin to form soft slabs high in starting zones during the midday before higher speeds allow deposition farther down in the ravines late in the day. Although they’re supposed to stay out of the W for the daylight hours you’ll want to keep an eye on their direction as a shift to the NW is expected this evening. A shift to the NW would likely produce even greater levels of wind transport.
Starting the day out we’re in a mix of Moderate and Low avalanche danger but expecting to climb the scale as we move into the second half of the day. Windslab development will first take place atop unconsolidated light density snow thus creating the the “upside-down snowpack” that we are taught to keep an eye out for. Because 3% snow has very little strength we expect to see small avalanches in many areas as winds ramp up. After one avalanche cycle wraps up in an area I would expect reloading of the same slope to occur with development of thicker and more dangerous windslab. This is most likely in areas with E aspects such as the Center Bowl in Tucks and the gullies from Odell to Central in Huntington. The areas on the periphery with N and S aspects will see cross-loading occur and we believe natural avalanches are possible late in the day. Some of these areas like Huntington’s Escape Hatch are far less of a concern than say the top of Pinnacle but the snow densities and forecasted wind may still cause avalanche activity to occur.
- 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