Avalanche Advisory for Tuesday, March 21, 2017

This advisory expires at Midnight.

 

Huntington and Tuckerman Ravine have LOW avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: This morning, areas of hard wind slab will be encountered on north facing aspects. East and south facing slopes received sun and warmth yesterday that refroze last night and should present more of a long sliding fall hazard than avalanche problem this morning. Snow showers through the day may bring up to 2” of new snow with increasing W and NW wind. Pockets of wind slab will develop, particularly in sheltered areas of westerly wind, creating and increasing avalanche hazard as the day progresses. These pockets will likely be isolated due to the small amount of incoming snow and soft due to lighter wind speeds.

WEATHER: Light wind, warm temperatures, and clear skies allowed the surface snow of east and south aspects to warm yesterday. Clouds developed overnight and should continue to thicken as the day progresses. As the cold front approaches, temperatures may spike for a brief period this morning before sharply dropping in the afternoon when the front arrives. The cold front contains some moisture which should create scattered upslope snow showers during the day with possibly up to 2” by tonight and another 2” by tomorrow morning, however, it seems likely this total will be on the lower side. Current wind on the Summit is NW at 21mph. This will shift to the W through the day and increase to 40-55mph by nightfall.

SNOWPACK: Wind slab on top of the old melt-freeze surface has now gone through multiple periods of warming, the most significant being yesterday. The warming on Saturday and Sunday was minimal and not enough to affect the stability of this slab. Yesterday, east and south facing aspects received a prolonged period of warmth. In places where the wind slab is thin, this warming likely penetrated through the slab and into the snowpack beneath. Overnight, the freeze will have created a strong bond between these two layers. In places where the slab was thicker, such as the Lip and Center Bowl, the warming weakened the tensile strength of the slab for a period yesterday afternoon but did not penetrate far enough for the freeze to improve the bond to the old surface. The cold last night will have frozen the moistened surface snow of these thick areas into a more cohesive slab, improving the overall strength of the snowpack. Areas that did not receive warming yesterday (north facing aspects) contained firm, wind-textured snow or large areas of older surface that will be largely unchanged today. New snow arriving today will be subjected to increasing wind from the west. If traveling in avalanche terrain late in the day today, be prepared to encounter isolated pockets of new wind slab in lee areas of west wind or tucked under terrain features.

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 8:15 a.m., Tuesday, March 21, 2017. A new advisory will be issued tomorrow.

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

2017-03-21