posted at 8:15, Monday, February 21, 2011
Tuckerman Ravine has CONSIDERABLE, MODERATE, AND LOW avalanche danger. The Sluice and Lip have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The Center Bowl, the Chute and Right Gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Hillman’s Highway, Left Gully, Lobster Claw, Lower Snowfields and the Little Headwall have Low avalanche danger. Isolated terrain features do contain pockets of instability in these Low rated areas.
Huntington Ravine has MODERATE and LOW avalanche danger. Central and South gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.
Falling temperatures, light snow showers and increasing winds can be expected today in the mountains. As a low pressure system passes by we can expect a trace to two inches of snow before high pressure edges into the region, causing temperatures on the higher summits to fall to around -10 F (-23 C) with increasing NW winds that are forecasted to reach speeds of 55 to 75 mph (88 to 120 kph) with higher gusts this afternoon. The Summit recorded 0.8″ (2 cm) of new snow as of 7 am and the radar isn’t snowing much more on the horizon. Even though snow totals are forecasted to be light, you need to keep an eye on new snow accumulation today as it may increase the avalanche danger. Today’s winds will be ideal for transporting new snow into the Ravines and creating new wind slabs. Right now I expect new slab development to be in the form of isolated pockets with the greatest potential in the Bowl of Tuckerman. If we end up with two or more inches of new accumulation expect more extensive slab development that could push some areas posted at Low into the Moderate rating.
Existing snow conditions vary widely from a crusty layer to deep slabs of varying density. After last week’s thaw, the mountain picked up around 6-7″ (15-18 cm) of light density snow. This was transported by NW winds on Saturday causing natural avalanches in both Ravines. The most notable avalanches from this event occurred in the Chute, Center Bowl and Lip in Tuckerman Ravine and in South Gully in Huntington Ravine. Early Sunday morning winds peaked over 100 mph (161 kph) on the Summit causing a number of forecast areas to become scoured out down to a crust layer that has developed from the thaw and subsequent cold temperatures. Additional wind loading continued yesterday on lighter winds adding snow to existing slabs and creating some new ones as well. Current stability varies greatly from one place to the next. Left Gully, Hillman’s Highway and the gullies posted at Low in Huntington are dominated by the crust layer but you may find an isolated pocket of new snow here and there. The Lobster Claw and Lower Snowfields are posted at Low but do have more new snow in them than the areas I just mentioned. Good route finding skills will keep you out of trouble in these areas. With the exception of the Center Bowl, areas posted at Moderate in both Ravines are currently on the lower end of that rating. Larger deposits of wind slab can be found but an avalanche savvy mountaineer could find a safe route through these forecast areas though careful snowpack evaluation will be important. As usual, the areas of most concern are in the Lip and Sluice in Tuckerman. These have the greatest amount of wind deposited snow and have the best potential, in addition to the Center Bowl and Chute, to pick up additional wind transported snow today, adding to the current stability issues. I expect visibility to be limited for a majority of the day. This should factor into your route choice. It has been a busy holiday weekend and you never know when someone will opt to descend above you putting you at the mercy of their ability to assess snow stability.
- 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