Avalanche Forecast for Tuesday, January 7, 2020
This information was published 01/07/2020 at 7:11 AM.
The Bottom Line
New snow and wind will combine to form new drifts keeping the avalanche danger at MODERATE today. Human triggered avalanches are possible in steep terrain where drifts form. An avalanche today may be on the small side, but could be large enough to carry and bury a person in a terrain trap. More snow overnight may bring increasing avalanche danger by morning tomorrow.
Yesterday, clear skies turned to snow showers on a strong west wind, snow intensifying briefly in the late afternoon and continuing through the night for a total of 2.2 inches recorded on the summit. Today, a trace to 1” of snow is possible early in the day as the low moves out providing a window of clearing skies before the next weather system moves into the region. Temperatures today will rise to the upper teens F with W wind 50-65 mph, decreasing to 15-30 mph in the afternoon hours. Clouds return this evening with 1 to 2 inches of snow overnight on W wind 20-30 mph followed by an additional 1 to 3 inches of snow tomorrow. Wednesday will be COLD! High tomorrow of only 0 F and NW wind increasing to 65-85 mph with gusts over 100mph late.
Primary Avalanche Problem – Wind Slab
The 2 inches of new snow yesterday afternoon/evening fell on west wind building on our wind slab avalanche problem. Carefully evaluate the terrain looking for smooth, rounded drifts of snow that may feel hollow under foot. Avoid this avalanche problem today by keeping to low angle terrain, or terrain where the wind has scoured more snow rather than drifted/collected snow.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
We are in a decidedly active weather pattern this week with quickly passing, almost insignificant systems that result in an inch or two of snow. Saturday: 2.6”, Sunday 2.2”, Monday: 2”, with a chance for 1 to three inches of snow tonight and tomorrow. Some of you may remember a quote from a previous MWAC Snow Ranger who would call this “Nickel and Diming”. These multiple, small weather systems don’t get much attention, but they add up and with each occurring one after the other with little time for snow settlement. Don’t let your guard down, the avalanche problem is more than just the two inches of snow that fell yesterday.
The Lion Head Winter Route is open and remains the safer choice for accessing the summit of Mount Washington from the east. An ice axe and crampons are needed near treeline and above with micro-spikes useful in wind scoured areas.
Conditions on the Sherburne ski trail have improved with the recent snowfall though a few rocks and ice patches have emerged.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.
Safe travel in avalanche terrain requires training and experience. This forecast 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.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 01/07/2020 at 7:11 AM.
Jeff Fongemie, Snow Ranger
USDA Forest Service
White Mountain National Forest