Avalanche Advisory for Wednesday, April 4, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. 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. Evaluate snow and terrain carefully to identify features of concern. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: Wind slab forming from new snow and wind later today is our primary avalanche problem. These potentially sensitive but likely small slabs may form in the brief window of snowfall and elevating westerly winds forecast to occur this afternoon through tonight. The minimal snow followed by a wintry mix of precipitation including freezing rain which occurred last night has not created new avalanche concerns. Today’s weather will directly drive any increase in avalanche danger. If we see higher snowfall totals with less rain and mixed precipitation, increasing wind late today will build larger wind slabs. A higher proportion of liquid precipitation will result in smaller, if any, new unstable slabs.

 WEATHER: A warm front is currently driving the transition from snowfall overnight towards sleet and freezing rain, and should soon result in all precipitation this morning falling as rain. Hermit Lake and the Summit both recorded around ½” of snow in the last 24 hours. As the day progresses, a cold front will approach as winds shift from the current SW to W and increase and possibly gusts over 100 mph. The cold front will shift our precipitation back to snow as temperatures drop sharply from a summit high near 40F to a low below 0F tonight. Forecasts are currently showing a relatively late changeover to snow from rain, with a total of 0.8 inches of water falling in some form today. An earlier arrival of the cold front will result in more snow, and a late arrival will result in less. In total our terrain could receive anywhere from 3-7 inches of snow before snowfall tapers by tomorrow morning. Wind should shift NW and remain near the century mark on the summit overnight before slackening tomorrow. We could receive another trace to 2 inches of snow tomorrow as temperatures remain cold.

SNOWPACK: The timing of frontal passages today will determine snowfall totals and ultimately drive the building of unstable slabs. While the size of new slabs will vary according to how today’s weather actually plays out, we expect any period of elevated avalanche danger to be brief and ultimately minimized by the scouring effect of sustained winds near 100 mph overnight. By tomorrow morning, new snow in our terrain will likely exist only in isolated pockets of generally firm wind slab and refrozen hard snow should be the dominant surface. Our upper snowpack still retains distinct layers, with the melt-freeze surface layer lying on drier firm snow which sits on the robust January melt-freeze crust. It’s plausible that today’s moisture and warming will briefly increase instability of these old layers, but we don’t expect avalanche activity before the sharp drop in temperature refreezes our upper snowpack tonight. Long sliding falls will likely return as your primary objective hazard by tomorrow.

 The Harvard Cabin is now closed for the season. The only place to camp in the Cutler River Drainage is at Hermit Lake Shelters.

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.
• Posted  8:00 a.m., Wedesday, April 4, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858