Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding and conservative decision making is essential. The only exception to this is the Little Headwall and the Escape Hatch which are Moderate. Natural avalanches are unlikely and human triggered avalanches are possible.
My mind went into overdrive this morning weighing all the complex factors for today’s ratings. Let’s jump right in and get our hands around this slippery dragon.
Over the past 24 hours we picked up 2.6” (6.6cm) of snow on the summit and about the same at our Hermit Lake and Harvard manual snowplots. The vast majority of this fell as rimed crystals, most of which were fully developed graupel, the ball-bearing of the snow crystal world. Over the past 72 hours the summit and the lower plots received between 5 and 6” (12.5-15cm) which has blown in on moderate NW, N, NE, and E winds. Yesterday’s ball-bearings came in on E winds which cross loaded N and S facing aspects and pooled on other aspects. Areas beneath steep slopes and ice facing E, into the wind will also have stability issues to be aware of due to the catchment and pooling of graupel on benches and lower angled terrain. Expect a wide degree of spatial variability to develop today as an additional 1-3” (2.5-7.5cm) falls on an E wind from 25-40mph (40-65kph) with higher gusts. The developing problem will be two-fold:
New loading will build slabs over graupel that exists in varying depths. Some “sweet spots”, or weaknesses more susceptible to fracture and failure, will occur over these pooled areas.
Generally light to moderate winds for Mount Washington will develop touchy delicate slabs in many areas sheltered from E winds which will load on top of the past 9 days of snow. Some stepping down to deeper layers may occur.
If the weather forecast holds true we will have seen between 7-9” of snow over the past 4 days, coming in on moderate E wind velocities. Most areas are starting the day on the upper end of the Moderate rating moving into Considerable this afternoon as snow picks up and winds increase. Areas to watch on the top of my list are the south facing slopes of Tuckerman from the Lobsterclaw over to the Lip, and at the base of steep pitches of ice in Huntington even though they have an easterly facing component, this is due to graupel sluffing. The base of South, Odell, Pinnacle, Central and North are some examples. Winds tonight will ramp up, gusting into the 60’s mph ( 96+kph) creating peak instabilities after dark. Tomorrow I think hidden trigger points of ball bearings will be the main issue to be aware of and realize stability tests may give you “false stables”. Keep this in mind as you travel today and Friday by keeping your evaluations in perspective and anticipate changing stability as you move. My next concern may be the intense solar gain on Saturday affecting the southern aspects. More on this issue later.
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 8:40am, March, 7th 2013. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856