Avalanche Advisory for Tuesday, January 2, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. North, Damnation, and Yale gullies have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. Lobster Claw, Right Gully, Lower Snowfields, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: The arctic air parked over our region continues to slow stabilization of slabs deposited over the past week. This factor couples with a highly variable upper snowpack to prevent us from dropping below a Moderate rating for much of our terrain. Areas where the wind slabs formed in the last week are most smooth likely pose the greatest stability concern. Remember that these firm slabs, though stubborn to a human trigger, have the ability to propagate a large fracture and that you are most likely to initiate a fracture in thin areas. We don’t expect snowfall forecasted late today to accumulate and pose a stability concern before dark, but be aware that small and touchier slabs could build overnight.

WEATHER: Our consistent and frigid weather should give way to a change by the end of the day. Snow showers this afternoon and tonight could bring anywhere from a trace to 5” of new snow. Summit temperatures have hovered around -20F for the past 24 hours and will slowly rise today through tonight to reach the positive single digits by tomorrow. NW wind should increase towards 70 mph while shifting W by the end of the day and diminish overnight to summit wind of 30-40 mph tomorrow. Thursday could bring a stronger low pressure system and additional snowfall.

SNOWPACK: Our upper snowpack formed over the past 10 days continues to hold potentially weak layers as cold air inhibits strengthening of bonds. We expect these slabs to remain stubborn though not impossible for a human to trigger. Slab thickness varies greatly, which provides a tricky situation for travel decisions and applicability of stability test results. This spatial variability also means that while low in likelihood, a human triggered avalanche could be large. Facets growing near the December 23rd crust, where it is still present, continue to contribute to the dynamic nature of our snowpack. We haven’t yet seen evidence for this potential weak layer to be particularly reactive or be associated with a strong fracture propagation. It continues to be relevant, though its current low likelihood of producing a sizeable avalanche prevents us from shifting towards persistent slab as our primary avalanche problem. Of equal or greater concern could be new snowfall tonight and potentially again on Thursday.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin 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 7:30 a.m., Tuesday, January 2, 2018. A new advisory will be issued tomorrow.

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

2018-1-2