Avalanche Advisory for Monday, March 12, 2018

Huntington Ravine has Considerable and Moderate avalanche danger. Yale, Central, Pinnacle, South, and Escape Hatch Gullies have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. North, Damnation, and Odell Gullies have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern.

 Tuckerman Ravine has Considerable and Moderate avalanche danger. Right Gully, Sluice, Lip, Center Bowl, Chute, and Hillman’s Highway have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lobster Claw, Left, and the Lower Snowfields have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. The Little Headwall is rated Low due to a less developed snowpack.

 AVALANCHE PROBLEM: Wind slab formed in the past two days covers most of our terrain and is our primary avalanche problem. These smooth surface wind slabs were formed by W to NW wind which either directly loaded or cross loaded most forecast areas. In many areas, this somewhat soft but cohesive surface snow overlies slabs formed late last week that are similar if a little less soft in character. We expect all smooth surface snow to be sensitive to a human trigger today. The connected and consistent nature of wind slab means that such avalanches could be quite large. Upper portions of Left Gully and most of Odell have heavily wind textured snow at the surface that will be fairly hard and more stubborn to a human trigger, hence their Moderate rating. One if not two natural avalanches in Lobster Claw yesterday have reduced snow available to avalanche, though sensitive pockets likely still exist. Moderate avalanche danger means that human triggered avalanches are possible, suggesting that you should evaluate snow and terrain carefully prior to committing to a slope. It’s not likely you’ll be able to avoid the avalanche problem in Moderate rated terrain today. It’s a beautiful day to enjoy the mountains, so carefully evaluate all snow and terrain. Choose to come home safely.

 WEATHER: Yesterday we picked up nearly 1.5” of 10% snow at Hermit Lake with over 3” recorded on the summit, while the winds out of the WNW decreased steadily overnight. Today we expect summit wind to stay relatively light but shift in direction to the E, increasing to 15-30 mph this afternoon and 30-50 mph overnight.  The incoming low pressure system will bring cloud cover to our currently clear skies with snow expected to start this evening.  The storm should begin slowly then escalate quickly early tomorrow morning.  As the snowfall increases so should the winds, shifting from the E to the N and increasing to 50-70 mph with gusts to 80.  This system is expected to bring 12”-19” to most summits with some areas closer to 24”.  There is a winter storm warning in effect from 4am Tuesday to 2pm Wednesday.

SNOWPACK: The sustained W and NW wind over 70 mph late Saturday was followed by lighter wind yesterday and created wind slabs with some variance in character. More sheltered areas which had lighter loading have relatively soft (4F+) slabs while areas receiving more direct loading likely hold slightly less soft (1F-4F) wind slabs. That said, the surface snow in our terrain is remarkably similar in appearance and is well connected. This cohesive surface snow overlies slabs formed earlier last week that are similar if a little less soft in character. Beneath this new slab or combination of recently formed slabs is the old ice crust that could ultimately be a bed surface for avalanches initially releasing on this layer or nearer to the surface and ultimately stepping down. Weather today should not place additional load on the snowpack, making natural avalanches less likely, but a human triggered avalanche remains likely in much of our terrain.

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 Harvard Cabin.
• Posted 8:10 a.m., Monday, March 12, 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

2018-3-12