Avalanche Advisory for Wednesday March 19, 2014

Expires at Midnight

Tuckerman Ravine has Moderate and Low avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, Hillman’s Highway, and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lobster Claw, Right Gully, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.

Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, Odell, South, and the Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. North, Damnation, and Yale gullies have Low avalanche danger. Natural and human triggered avalanches are unlikely.

AVALANCHE PROBLEMS: Wind Slab created at the tail end of the weekend into Monday is the #1 problem today. Our largest snowfields with an E and SE facing component such as the Lip, Center Bowl, and Central Gully, as well as smaller cross-loaded slopes from W and NW winds, are the main locales holding these slabs. Deeper Persistent slabs are problem #2, and primarily exists due to faceting around the dominate crust layer buried at various depths depending on location. Other persistent weaknesses can be found, but play as a backseat problem compared to the aforementioned crust facets. All of these persistent problems could be the primary failure leading to an avalanche from human triggers. But a step down failure into these facets caused by an overrunning wind slab avalanche is more plausible.

WEATHER: Temperatures have been steadily climbing since Monday night and are expected to hit around 20F on the Washington summit today. Winds will pick up from the light winds we’ve had over the past day. W winds will shift to come from the S, and increase from 20 to 50 mph, bringing clouds this afternoon. Precipitation is anticipated to start in the form of light snow showers this afternoon as a prelude to the Winter Weather Advisory that comes into effect at 8pm tonight. We are expecting about 4” of snow overnight into tomorrow, perhaps mixing in with other frozen “wintry mix” particles. Below Hermit Lake we could see rain signifying the temperature regime will be very close to the freezing mark.

SNOWPACK: As Jeff referred to yesterday, high weekend winds have filled in the vast majority of crown lines causing some pretty intense variability around the Ravines. The main issue to pay attention to in your travels is the reactivity of the newest upper wind slabs. They will offer a variety of hardness based on being either exposed to the high winds, or being protected from them. I would mostly be looking out for two general wind slab issues. First would be thin hard slabs that could propagate a fracture into the deeper adjacent terrain leading to failure/avalanche. And secondly, softer slabs on steep slopes near terrain features that protected loading snow from getting wind pounded. These near surface wind slab issues are followed by keeping a keen eye for “persistent” problems presenting as deeper weaknesses. Spatial variability will make it difficult to make assessments in one location and extrapolate the findings to another. Frequent stability tests are prudent.

Early solar gain will play a bit more of a role than it did yesterday for south facing slopes as temperatures get quite a bit warmer than Tuesday. However, as we move into the afternoon, winds will come from the south and increase, which will help cool these southerly aspects. Additionally, thin clouds will increase in thickness dramatically limiting potential heat. This brief heat should help the snowpack stabilize a bit, but not push too hard causing instability. The big issue late today and tomorrow is the snow coming on S and SW winds, shifting W tomorrow and increasing. Expect a loading event through tomorrow with an elevated avalanche danger.

Please Remember:

1. 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. 2. Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. 3. 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 8:33a.m. 3-19-2014. A new advisory will be issued tomorrow.

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

2014-03-19 Print