Avalanche Advisory for Monday 3-18-2013

This advisory expires at 12:00 midnight tonight.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Lobster Claw, Right Gully, Sluice, the Lip, Center Bowl, and Chute all 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 in those locations.

Huntington Ravine has LOW avalanche danger. Natural and human triggered avalanches are unlikely in all forecast areas in Huntington Ravine. Watch for unstable snow in isolated terrain features.

Yesterday’s high winds moved around the relatively low density snow that had been deposited by recent storms. The areas rated Low were predominately scoured by the wind and Moderate areas developed windslab. Good visibility and light wind will allow excellent conditions for assessing the snow today as you travel around the mountain and temperatures will warm as winds shift to the southwest.

Field observations this morning revealed the degree to which scouring occurred in Huntington Ravine.  You might never know we received 16.2” (41cm) of snow since Thursday by looking into the ravines. Crown lines and debris from natural avalanches that occurred over the last several days were, by and large, erased by winds blowing steadily out of the NW in the 60 mile per hour (100kph) range with gusts over 80mph (130kph). Winds blowing this long at that velocity reduce the fresh snow into smaller particles which pack more easily and form stronger bonds than when they exist in the larger, original forms. That said, I would still be on the lookout for places in areas forecasted at Low where the snow may have formed pillows behind lee features.  The wind was not as strong as it can be here so the scouring did not completely eliminate the hazard.  In Central Gully, for instance, near the final choke point near the upper rock band, a smooth pillow of snow would command my attention if I were climbing it today.  I’d also dig around in other areas to be sure that I wasn’t standing on a larger surface of windslab with a weaker layer way down near the ice crust.

Tuckerman Ravine looks as it often does after a windy period. The upper start zones in the Moderate rated areas are blown into hard, textured sastrugi while softer smoother and possibly sensitive wind slabs grace the midsection. This is particularly true of Right Gully, the Sluice and the Lip where large, smooth pillows exist. An experienced party exercising solid avalanche travel and assessment skills might be find decent riding in the mid-section of Lobster Claw or Right Gully though it will be limited by scoured hard surfaces above and below. The Lip through Center Bowl and into Chute may also harbor softer snow, though the hazards of traveling in these sections are greater and more difficult to mitigate. Left Gully and Hillman’s Highway have pockets of wind slab to avoid or assess as well.

Overall, a nice day to be out and about during this calm before the storm. We will be making field observations today in anticipation of a significant snow storm starting this evening.

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 9:00a.m. March 18, 2013. A new advisory will be issued tomorrow.

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

2013-03-18 Printable