This advisory expires at midnight, Saturday 3-03-2012
Tuckerman and Huntington Ravines have HIGH avalanche danger today. Natural avalanches are likely and human triggered avalanches are very likely. Very dangerous avalanche conditions exist on a variety of slope aspects and angles. Travel in avalanche terrain is not recommended, including run-out paths. The only exception to this is the Little Headwall which has Moderate avalanche danger.
The old adage, “you don’t know where you’re going if you don’t know where you’ve been” is a perfect sentiment to capture our developing avalanche situation today. Let’s back up a couple of days. On Thursday our most recent storm hit the mountains, dumping about 12” (30cm) on the Presidential Range. Overall snow densities where light, averaging about 7% with the last 4” (10cm) being around 4%. During and since that snowfall, winds have been quite light for Mount Washington, averaging about 28-29mph with brief gusts over 45mph on Thursday. Through most of Friday, summit winds hovered around the 20 mph mark. Down at the horizon of the Ravines, at approximately the 5000ft level, wind speeds were less, leaving our new fluffy blanket fairly unaffected except in the more exposed locations. Then at midnight, several hours ago, snow began falling again with an increasing wind. By 3:30am, Washington’s summit was averaging about 60mph, gusting to 74mph, from the South. After relative calm period, I can almost hear it yelling, “hey guy’s I’m back, what’ya been doing?!” Winds today are forecasted to shift, walking clockwise from the current S towards the W. As winds shift to our prevailing directing and continue to build speed, our east-facing Ravines will get overwhelmed with the left over storm snow lying in the alpine zone. This is particularly true in Tuckerman due to Bigelow lawn, a flat plateau the size of 600 football fields. This area sits above the Ravine right in line for winds with a westerly component, providing an incredible supply of snow to be moved. I would expect more than one avalanche cycle out of this event as slopes get reloaded, cocked to fire, and the trigger pulled by the final flake and gravity tugging on steep slopes. The light densities will also make cross loading of S-facing areas easier than usual. Although these slopes will not harbor the dangers of N and E aspects today they will still likely produce natural avalanches. In areas such as Damnation and North, avalanche activity may be limited to smaller slabs and sluffs, but these can still easily knock you off a stance. To add to this entire situation, new snow has been falling over the last 4 hours and is expected to continue through the day, perhaps changing forms into a bit of a “precipitation grab bag”. The summits forecast is for 2-4″ (5-10cm) of snow, sleet, and freezing rain, maybe even followed by rain. As these heavy forms of precip fall, any pre-existing instabilities will rapidly become worse.
All of this history and current weather translates quickly and definitively into today’s rating of “HIGH”. All of our forecasted slide paths have fully developed tracks so you can expect full avalanche runouts to occur. Although the light density snow can be easily picked up for transport today, crystals will be pulverized into small grains as winds increase, making for denser slabs packed in the deposition. This increased mass may push some avalanches full path, criss-crossing the floor and approach fans of both ravines. Travel in avalanche terrain, which includes run-out paths, is not recommended. As blowing snow and clouds will offer very limited visibility, going into the Ravines just to look won’t give you much more than placing yourself as lead pin in the bowling alley.
The warmth that is expected today won’t last too long. Probably just long enough to make a mess of the nice snow at lower elevations, such as on the Sherburne Ski Trail where the lower sections are currently getting a freezing rain coating. Overnight, mountain winds will start to crank up, perhaps blowing over 100mph for a short time, then decreasing again into good wind-loading velocities. Tomorrow’s avalanche danger will depend in large part on avalanche activity today, more snowfall overnight and tomorrow, and whether or not the overnight winds were able pummel any gullies into full submission.
- 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 8:05a.m. 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