Posted 8:20a.m., Tuesday, March 1, 2011
Tuckerman Ravine has CONSIDERABLE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely. The only exception to this rating in Tuckerman Ravine is the Little Headwall which has Low avalanche danger. In this area natural and human-triggered avalanches are unlikely.
Huntington Ravine has MODERATE avalanche danger today. Natural avalanches are unlikely and human-triggered avalanches are possible.
Good morning March. We hope that you can give to us what February lacked. We didn’t have a single day that we picked up more than 10″(25cm) of snow and our precipitation’s liquid equivalents for the month came in at about half of the historical average. We hoped that February would end with a bang but yesterday’s storm didn’t pan out quite like we expected. Then again how often do they? I’m not hating, just stating the facts my friend. As predicted yesterday we received snow and then mixed precipitation and then some more snow. Where the forecasts seemed to diverge from what actually happened is in the snowfall accumulation department. Most forecasts were calling for 8-10″(20-25cm) but the Observatory only recorded 1.9″(5cm) from midnight until midnight and then an additional 1.1″(3cm) from midnight to 6AM this morning. At Hermit Lake we picked up 4.1″(10.5cm) with an average density of 16% and at the Harvard Cabin we found 4″(10cm) of fresh snow with a slightly higher density. New snow was blown in on winds that wrapped from the S through the W and eventually to the NW. This progression has allowed significant wind loading to take place on all aspects and if we could see more than a stone’s throw I’m sure we’d be looking at some good debris piles and fracture lines. Wind speeds climbed during this clockwise progression and once they made it to the NW they started holding steady around 90mph(145kph) with gusts over 100mph (161kph). These speeds often scour some of our slopes rather than load them with new windslab and we expect this phenomenon to have occurred to a degree in Huntington. One factor that is present and limits scouring is the high density nature of the snow. Much of what we received was perfect snowball snow with a high water content that packs together nice and tight. During the early hours of the storm moderate winds deposited dense windslab that is resistant to wind erosion. For this reason I don’t believe scouring will be as widespread as it would have been with lighter and drier snow. If you venture into avalanche terrain today you’ll likely find stability issues no matter where you travel but scoured areas of exposed old surface may provide a route to avoiding these issues. Natural avalanches will continue to be a threat through the morning hours especially in the areas rated Considerable that have a SE aspect such as the Center Bowl, Lip and Sluice in Tuckerman. As winds die down to 60mph (97kph) later today we’ll see loading diminish and the threat of natural activity will drop. The potential for human-triggered slides will remain especially with forecasted temperatures that will only reach the single digits (F).
The Sherburne Ski Trail picked up some good snow from this storm but a rain crust topped it off yesterday afternoon. Although freezing rain and drizzle were reported all the way to the summit the crust that developed at mid elevations is definitely thinner than what you’ll find on the lower parts of the Sherburne. Consider doing a couple laps on the upper section and then chopping up the lower section once you’ve got your game on.
- 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