This advisory expires at Midnight.
All forecast areas in Huntington and Tuckerman Ravine have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding and conservative decision making is essential.
AVALANCHE PROBLEMS: Wet Slab avalanches are the primary concern today followed by the Wind Slabs that developed over the last few days. Forecasted warm temperatures and rain will load and weaken the snowpack. The degree to which this occurs will depend on the amount and type of precipitation that falls, and the strength of the slab that it falls on. Thinner areas of slab could react first with less liquid precipitation than areas of thicker slab, but any avalanche could entrain more snow or step down to deeper weaknesses. Wind Slab is also still a hazard today from the last 72 hours of snow loading. New Wind Slabs may develop in steep, lee areas in the event that precipitation falls as snow and not rain.
WEATHER: Avalanche terrain will see all forms of precipitation today. Expect a little snow, sleet, freezing rain, and then rain reaching all the way to the highest summits. Temperatures as of 6am show both Hermit Lake and the Washington Summit at about 27 degrees with a colder band in between. This could affect varying precipitation types for a short period until full air mixing occurs. It is possible that the summit could get some rain while areas in the ravines get freezing rain building an ice crust. In the end, all precipitation forms should melt down to about 0.35″ (0.8cm) of water being brought to the mountains on a S wind building from 30 (48kph) to about 60mph (96kph). Tonight the mercury will fall into the teens F, winds will shift back to the W and increase, and 1-3″ (2.5-7.5cm) of snow should fall. If this does play out, anticipate new cold snow avalanche concerns for Saturday.
SNOWPACK: The main concern today is what rain may do to snowpack stability. The ratings today are taking into account the potential for upwards of .25-.35″ of rain. Many areas may handle this fine, particularly locations of deep hard slab. But we cannot say this about all areas confidently. Rain adds weight, decreases strength by melting bonds, and can pool on buried ice layers lubricating that potential bed surface. A Wet Slab avalanche is often destructive and its mass is conducive to stepping down to other weaknesses and becoming larger. The hackles should always go up when rain falls on a cold snowpack. If you have seen the ravines or photos of the ravines in the past several days, you’ve witnessed the substantial growth of our snowpack. Fans of spring skiing should be elated by this development. The incessant Mount Washington wind has loaded 54″ of new snow into our terrain so far this month. While it is not a banner year for snowfall like our southern neighbors are experiencing, we are at least back on track for a fairly normal looking year. Moving around the terrain now, you’ll notice that our snow surface and consequently our current and future bed surfaces have smoothed out, covering over rocks, boulders and bushes in many areas. This means a couple things. One is that avalanches can grow larger and generally run further than previously. Secondly, these rocks and bushes are no longer in a position to serve as anchors and in fact may create the thin spot in the upper snowpack that helps create a crack, leading to either a natural or human triggered avalanche. Cold weather is returning after this shot of heat and water so anticipate another melt freeze crust to develop after the temperature drops tonight. New snow and high winds will then create a new set of avalanche problems to solve tomorrow.
- 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 7:15 a.m. 2-21-2014. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856