Avalanche Advisory for Sunday, 2-12-2012

Expires 12:00 midnight, 2-12-2012

Tuckerman Ravine has both CONSIDERABLE and MODERATE avalanche danger.  The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The Lobster Claw, Right Gully, Left Gully, and Hillman’s Highway have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. The Lower Snowfields and the Little Headwall are not posted due to an overall lack of snow. Forecasts for these locations will begin when conditions warrant.

Huntington Ravine has MODERATE and LOW avalanche danger. North, Damnation, and Yale have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features. All other forecast areas have Moderate danger. Natural avalanches are unlikely and human triggered avalanches are possible.

With temperatures falling to the lowest we’ve seen this winter, I suspect that traffic on the mountain will be rather light for a weekend day. It’s currently -16F (-27C) at the summit and -3F (-20C) at Hermit Lake. The cooling trend will continue into the overnight hours, ultimately dropping below -20F before temps begin to rebound. To be clear, these temperatures are the actual temperatures, not the wind chill. Winds today will remain strong, blowing from the NW around 55-75mph (88-120kph). Not only will this make the air feel a lot colder than it already is, but it will continue to blow yesterday’s snow from the west side of the mountain over to the east. Come well equipped for cold weather, even if your plan is just to do a fast lap on the icy Sherburne.

Not a whole lot of snow actually fell yesterday. The summit recorded 1.4″ of very light density snow. Down at Hermit Lake we observed about the same amount around mid-afternoon. While it fell, the winds were very light, which allowed a layer of weak snow to blanket the higher elevation terrain, including avalanche starting zones. On top of this light density blanket, increasing wind speeds began to transport the snow over the tops of the ravines. This created an “upside down snowpack” with denser, stronger layering on top of lighter, weaker layers below. Snowpacks such as this are responsible for a lot of the avalanches we have here each season.

Today’s ratings reflect a range of conditions you can find in avalanche terrain. In the Considerable rated areas, the amount of snow loading going on through today combined with the upside down effect lead us to believe natural avalanche activity is possible. The greatest potential for this is in the Lip and Center Bowl area. On the other end of the spectrum, the light density snow had a difficult time sticking to slopes exposed to strong overnight winds. The northern gullies of Huntington may have pockets of unstable snow in isolated lee areas, but the prevailing surface condition here will be stable older snow. Elsewhere in both ravines you will find snow that spans the entire range of the Moderate rating definition. Areas more prone to scouring, such as Hillman’s, Left, and much of Huntington, will have areas of unstable snow too large to call a “pocket” or “isolated terrain feature,” but a lot of the surfaces in these forecast areas will have generally good stability. Due to continued snow loading today, I wouldn’t completely rule out the potential for natural avalanche in these areas, but I believe the likelihood and overall avalanche hazard better fits into the Moderate rating. In Right Gully and the Lobster Claw, the overall lack of snow is keeping  reasonable travel options open despite their being in the direct lee of NW winds. On the climbers’ left side of these gullies is where you’re more likely to find areas of instability. Regardless of where you go, poor visibility will hamper your efforts to make accurate assessments from afar. With the weather being what it is today, you may want to be a little more conservative in your route choices.

Please Remember:

  • 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 8:50am. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

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