Avalanche Advisory for Wednesday, February 21, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger.  Heightened avalanche conditions exist on specific terrain features. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

 Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl and Chute have Moderate avalanche danger. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Watch for unstable snow on specific terrain features.

AVALANCHE PROBLEM: Our primary problem will be in the form of the skier or rider initiated loose wet avalanches which are trending towards likely today. Loose Wet avalanches which will be possible for a skier or snowboarder to initiate in steep terrain are our primary avalanche problem. Moderate rated areas held more soft snow at the surface prior to the current warm and wet weather and will be capable of producing large loose wet sluff and point release avalanches. While such avalanches would likely not bury you without a significant terrain trap, they can easily cause a fall and even carry you downhill. Realize that the steep terrain where loose wet activity is most likely to occur is also a particularly high consequence place to take a fall.

 If you venture into the terrain today, be aware that the record warmth is awakening a number of our typical spring hazards. Water flowing beneath the snow surface is creating areas of undermined snow that you could easily break through. Overhead hazards including icefall and to a lesser extent rockfall should be respected. When choosing terrain today, remember that these avoidable hazards have resulted in many accidents, some of them fatal. Don’t neglect to look at safer and equally rewarding options.

 WEATHER: The summit recorded 1.53” of rain during the early morning hours yesterday. The 24 hour high temperature reached 45F at this writing. It is still climbing and has reached 66F already at the base of the Auto Road. Though a down-valley breeze is keeping it cooler in valley locations, a record setting high temperature reading on the summit seems likely as mild air continues to pour into the area. Clear skies and sunshine will speed this warming early before a cold front brings clouds and a tenth of an inch of rain this afternoon and evening. A flood watch is in place for the area due to runoff and melt which serves as a good reminder of the emerging spring hazards. Winds will continue to ramp up from the current 70’s mph on the summit through the day with gusts well into the 90 mph range by sundown. Overnight gusts will reach near 110 mph.

SNOWPACK: Prior to this warmup, our snow surface was a mix of soft wind slab and hard refrozen crust. Rain and warm temperatures yesterday will continue today which will drastically change the upper snowpack. We expect that moisture has fully soaked and then drained from what was wind slab, resulting in less cohesion and minimizing concerns for slab avalanches from this layer. These areas will continue to hold the softest snow with the greatest potential for loose wet avalanches. The former crust surface should provide more dense snow, but could also allow loose wet activity as all snow continues to warm. Expect to posthole to at least your knees in much of our terrain this afternoon. The present hazards and sloppy conditions suggest that our alpine terrain may not be the most rewarding place to enjoy the sunshine today.

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 Harvard Cabin.
• Posted 7:45 a.m., Wednesday, February 21, 2018. A new advisory will be issued tomorrow.

Ryan Matz/Frank Carus, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-2-21